Department of Conservation Ecology and Entomology

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Assessing the chemical ecology and shelter-seaking behaviour of the grainchinch bug, Macchiademus diplopterus (hemiptera: lygaeidae) for optimisation of trapping during aestivation
(Stellenbosch : Stellenbosch University, 2016-12) Ngadze, Masimbaashe; Johnson, Shelley; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The grain chinch bug (GCB), Macchiademus diplopterus (Distant) (Hemiptera: Lygaeidae) is a key quarantine pest of South African export fruit and is endemic to the Western Cape Province. The pest is troublesome in the drier wheat growing areas where it disperses from wheat in summer to find sheltered sites in which to aestivate. Aestivating adults can end up contaminating export fruit. The aim of the study was to gather more knowledge on the chemical ecology and shelter-seeking behaviour of the GCB. The involvement of pheromones in the aggregation behaviour of GCBs is yet to be fully elucidated. Further investigating the chemical ecology of the GCB in order to optimize its pheromone trapping was the primary focus of the first research chapter in this study. Headspace volatile compounds were identified from active bugs through gas chromatography-mass spectrometry (GC-MS) analysis. A total of 14 volatile compounds were identified from males and females in varying concentrations. For both sexes pooled, tridecane, (E)-2-hexanal and (E)-2-octenal were the three main components; (E)-2-hexenol, (E)-2-octenol, decanal and pentadecane were in medium amounts, while decanoic acid, dodecane, hexadecanal, hexanal, icosane, nonanal and tetradecanoic acid were minor components. The efficacy of synthetic lures using previously identified aggregation pheromone components, and sex pheromone volatile components (identified in present study) was studied in combination with modified traps using rubber septa dispensers in a field trial. There was no significant difference (P > 0.05) between insects caught in the sex pheromone baited traps and the aggregation pheromone baited traps. Traps caught low numbers of GCBs compared to the level of orchard infestation indicated by the amount of bugs that were found sheltering in corrugated cardboard bands tied around tree trunks. The corrugated cardboard bands showed a significant difference in the number of bugs sheltering between bands placed at bottom and top positions (0.5m and 1.5m above ground respectively) on the trees, at site 1 (P = 0.0058), site 2 (P < 0.0169) and site 4 (P < 0.0496) with the exception of site 3 (P > 0.4115). Cardboard band position influenced catches, as more bugs were found in bottom bands. This can be used advantageously in optimising innovative trap placements in the future in order to improve catches. In the second research chapter investigations into the behavioural responses of GCBs to visual objects were conducted. This was done to increase knowledge on how this behaviour can lead to the development of control measures such as the use of coloured traps of different shapes. Behavioural responses of GCBs to different shapes presented in their visual space indicated that there was a significant difference (P = 0.0001) in the choice of shape. Vertical/upright rectangular shapes had the highest number of GCB visits. GCBs responded to upright rectangles of different colours.Black and red rectangles were not significantly different (P > 0.05) from each other but were both significantly different (P = 0.0001) from green and yellow rectangles, off-target and sedentary insects. Vertical rectangles of two different colour patterns (black & white) and (red & white) did not show any significant difference (P > 0.153) in the number of GCB visits. Both black & white and red & white vertical stripes were significantly different (P = 0.0001) from off-target and sedentary insects. This indicates that GCBs were equally responsive to both colour patterns. These results indicate that GCBs exhibit a positive scototactic reaction towards dark upright surfaces. Information generated from this study will facilitate the development of pre-harvest monitoring and management measures against GCBs, using pheromone traps and physical barriers that prevent GCBs from dispersing into fruit orchards at the wheat to fruit orchard interface. This can help to reduce fruit contaminations, ultimately lowering the rejection risk of export fruit from South Africa.
Assessment of the invasive German wasp, Vespula germanica, in South Africa
(Stellenbosch : Stellenbosch University, 2015-04) Haupt, Karla; Veldtman, Ruan; Addison, Pia; Prozesky, Heidi; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The invasive social wasp, Vespula germanica (Fabricius, 1793) (Hymenoptera: Vespidae), stands out as a remarkably successful insect invader worldwide. It flourishes in newly invaded ecosystems, where it has become a major problem in urban settings due to its close association with humans. The wasp is characterised by its devastating economic, social and environmental impact. Since its initial discovery in 1974 in Cape Town, all aspects of the wasp’s invasion throughout South Africa have been poorly documented. The wasp’s occurrence in the Cape Floristic Region (CFR) in the Western Cape Province (WCP), an area highly valued for its unique biodiversity, is of great concern due to the possible detrimental environmental effect of the wasp on this vulnerable biome. In this study, the present distribution of V. germanica was determined. Results indicate V. germanica’s distributional range is presently restricted within a small region of the WCP and it is thought that the Cape Fold Mountain range has acted as a natural barrier limiting the range expansion of the wasp. Field trials were conducted to determine V. germanica’s bait preference (protein versus carbohydrate) under local conditions and identify the best method in trapping the wasp. Fresh meats (lean smoked ham and minced beef) were overall the most preferred bait in both 2013 and 2014. Future studies should consider investigating the use of volatile meat extracts instead of fresh meat baits, as it could be as attractive but more practical for use in the field. Heptyl butyrate showed the most promising result of the artificial lures and warrants further investigation. Other lures (heptyl butyrate + acetic acid, isobutanol, isobutanol + acetic acid) were highly unattractive and possible reasons explaining this phenomenon, are discussed. A questionnaire survey was used during face-to-face interviews to explore the perspectives of forty farmers with regard to V. germanica occurring on their property. The current impact of the wasp in the agricultural context in the WCP was also determined. The majority of the respondents presented a negative view of the wasp and eradication seems to be a high priority for them. V. germanica is presently more of a social than an economic pest. Although indications are that with an increase in its density and distributional range, agro-economic problems and an increasing negative impact on local biodiversity can be expected. Management efforts should focus on its peripheral distribution, in order to curb further natural spread. The wasp’s distribution should also continue to be monitored, to enable early detection and rapid response, in the event that it succeeds in establishing itself in a new location. Further investigations into the suitability of a monitoring tool, including bait preferences, as well as continuing studies on the wasp’s overall impact, are recommended.
Assessment of toxic baits for the control of ants (Hymenoptera : Formicidae) in South African vineyards
(Stellenbosch : Stellenbosch University, 2008-12) Nyamukondiwa, Casper; Addison, Pia; Addison, M. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Ant infestations comprising the Argentine ant Linepithema humile (Mayr), common pugnacious ant Anoplolepis custodiens (F. Smith) and cocktail ant Crematogaster peringueyi Emery are a widespread pest problem in South African vineyards. Integrated Pest Management (IPM) programmes aimed at suppressing the problematic honeydew excreting vine mealybug Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae) on grapes must include ant control to optimize the effectiveness and efficacy of mealybug natural enemies. If ants are eliminated, natural enemies are able to contain mealybugs below the Economic Threshold Level (ETL). Current strategies for ant control are limited and generally include the application of long term residual insecticides that are detrimental to the environment, labour intensive to apply and can disrupt natural biological control if applied incorrectly. A more practical method of ant control using low toxicity baits was therefore investigated. Field bait preference and bait acceptance assessments aimed at determining bait repellency and palatability, respectively, were carried out during spring, summer and autumn in three vineyards of the Cape winelands region during 2007/08. Five toxicants comprising gourmet ant bait (0.5%), boric acid (0.5%), fipronil (0.0001%), fenoxycarb (0.5%) and spinosad (0.01%) dissolved in 25% sugar solution were tested against a 25% sucrose solution control. Gourmet ant bait was significantly more preferred and accepted by all ant species than the other baits. Laboratory bait efficacy assessments using four insecticides (gourmet, boric acid & spinosad) at concentrations of 0.25; 0.5; 1; 2 and 4 times the field dose and fipronil at 0.015625; 0.03125; 0.0625; 0.125; 0.25 times the field dose were carried out. Results revealed that boric acid (2%), gourmet ant bait (2%) and fipronil (1.0 X 10-5%) exhibited delayed toxicity for L. humile and C. peringueyi while spinosad (0.01%) showed delayed action on L. humile. Field foraging activity and food preference tests were also carried out for the three ant species during 2007/08. Foraging activity trials revealed that vineyard foraging activity of L. humile is higher relative to A. custodiens and C. peringueyi. This means fewer bait stations are required for effective L. humile control making low toxicity baits a more affordable and practical method of controlling L. humile than the other two ant species. Food preference trials showed that L. humile and C. peringueyi have a high preference for sugar while A. custodiens significantly preferred tuna over other baits. However, all ant species had a preference for wet baits (25% sugar water, 25% honey, tuna & agar) as opposed to dry ones (fish meal, sorghum grit, peanut butter & dog food). This research concludes that low toxicity baits show potential in ant pest management and can offer producers with a more practical, economical and environmentally friendly method of ant control which is compatible with vineyard IPM programmes.
The bio-ecology of the Cape grapevine leafminer, Holocacista capensis (Lepidoptera: Heliozelidae), in the Western Cape
(Stellenbosch : Stellenbosch University, 2016-03) Torrance, Leigh Ami Isbell; Addison, Pia; Geertsema, Henk; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The Cape grapevine leafminer, Holocacista capensis Nieukerken & Geertsema (Lepidoptera: Heliozelidae), occurring on Vitis vinifera L., has recently become of economic importance in the Western Cape, South Africa. The leafminer is of quarantine importance as cocoons are often attached to grape bunches intended for export when grapevine infestation is severe. Fortnightly monitoring efforts have indicated the occurrence of several overlapping generations within a growing season which are likely to affect potential management strategies. Adult and larval abundances tend to increase as the grapevine growing season progresses and as temperatures increase. A peak in adult and live larval abundance is reached between February and March, usually after harvest. The severity of leafminer infestation may be affected by the location of a vine within a cultivated block and strong evidence suggests that structural aspects (i.e. the trellis system used) affect the invasion potential of H. capensis. The leafminer tends to overwinter in the larval or pupal life stage within a cocoon which is often sheltered under the bark on the stem of a grapevine, in leaf litter or in a small crevice of a trellis post. Male moths have been detected throughout the colder winter months suggesting that small fluctuations may affect the developmental rate of overwintering pupae depending on the shelter experienced by cocoons. It is a possibility that adults produce offspring in surrounding foliage or are sourced by such refuges, although it is likely that eclosed adults undergo diapause and contribute to the first generation of leafmining larvae as soon as conditions become favourable. Pheromone baited traps, placed throughout the Western Cape, have indicated the presence of the moth in two of the largest table grape producing regions, namely the Berg River and Hex River Valley. The overall distribution of the moth has proven to be far more extensive than previously thought and may be present throughout southern Africa based on herbarium samples that yielded symptoms of leafminer damage. Monitoring strategies should be conducted as early as possible within a grapevine growing season to avoid severe infestations and unnecessary chemical applications depending on the bunch infestation tolerance. At an economic threshold of 5% bunch infestation, the commencement of management strategies is recommended when 442 adult male moths are caught per trap per fortnight. Results suggest that bunch infestation could be prevented altogether if management strategies were implemented when less than 87 adult male moths are caught. In cases where bunch infestation has occurred and post-harvest cold treatments are considered, a cold-treatment exposure of no less than 26 days at -0.5°C should be considered if 100% mortality is desired. Parasitoid wasps associated with the leafminer have been identified and could potentially be used in the area-wide control of H. capensis. A variety of chemical compounds have been used to control leafminer infestations in the past, although preventative applications of spinetoram seem to have had the most success in preventing infestation. Management strategies in line with the ideals of current Integrated Pest Management strategies should be explored in future research endeavours.
Biological and ecological factors contributing to the successful use of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) under South African conditions
(Stellenbosch : Stellenbosch University, 2011-12) De Waal, Jeanne Yvonne; Malan, Antoinette P.; Addison, M. F.; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) is a devastating pest of pome fruit in temperate regions of the world. Control of this pest, previously involved the extensive use of broad-spectrum insecticides. However, concerns over human safety, environmental impact, widespread dispersal of resistant populations of codling moth and the sustainability of synthetic pesticides in agroecosystems, has encouraged the development and use of alternative environmentally-friendly pest management technologies including the use of entomopathogenic nematodes. These nematodes are lethal pathogens of insects and belong to the families Steinernematidae and Heterorhabditidae, and are ideal candidates for incorporation into the integrated pest management programme currently being developed for residue-free pome fruit production in South Africa. The biological and ecological factors pertaining to the successful use of these nematodes for the control of codling moth were investigated in this study. Their use for bin-disinfestations was evaluated, focusing on the optimum handling conditions to ensure the survival and subsequent efficacy of the nematodes. The study proved that the local isolate SF41 of Heterorhabditis zealandica Poinar 1990 could be used for successful bin-disinfestation. The use of the same nematode isolate was also investigated for the disinfestation of mulch layers of diapausing codling moth larvae. An insect containment device which allowed for direct trial efficacy evaluation was identified and ecological factors pertaining to the successful use of nematodes for mulch disinfestation were investigated. The biological control potential of local nematode isolates, which had previously never been tested against codling moth larvae, was investigated in the laboratory under conditions as can be expected during orchard applications. The efficacy of the selected isolates was confirmed in field experiments. Innovative insect containment methods for above-ground trial efficacy evaluation in the field were investigated. Desiccation proved to be the most limiting factor to the survival and subsequent efficacy of the nematodes during field applications in temperate regions. The effect of low moisture levels on H. zealandica’s efficacy to control diapausing codling moth larvae was subsequently investigated and a starch-based formulation was further tested to overcome the issue of desiccation. Conclusive results indicated that there were several biological and ecological factors influencing the survival of nematodes and illustrated how these factors could be manipulated to overcome these issues and thereby ensure the efficacy of treatments. This is the first report of its kind to comprehensively investigate the use of South African entomopathogenic nematodes for the control of diapausing codling moth larvae and all results emanating from the study can be integrated into a framework for the commercial use of these nematodes in this regard in future.
Biological control of the banded fruit weevil, Phlyctinus callosus (Schönherr), using entomopathogenic nematodes and fungi
(Stellenbosch : Stellenbosch University, 2018-11) Dlamini, Bonginkhosi; Addison, Pia; Malan, Antoinette P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The overall aim of this study was to establish guidelines, from research undertaken mainly in the laboratory, and from field application, for the use of entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) to control the banded fruit weevil (BFW), Phlyctinus callosus (Schönherr), in vineyards and apple orchards in the Western Cape province. Discovering new species of entomopathogens is important, as more virulent, locally adapted species can be used to increase the potential of microbial control. The first objective of this study was to survey for EPNs and EPF strains/species in orchards and vineyards of the Western Cape, and to investigate their potential to control the BFW. The most virulent EPN species for the biological control of the BFW were selected in laboratory bioassays, and a field trial using Steinernema yirgalemense at different concentrations was conducted. In a further study, the best EPF strains for the biological control of the BFW were selected in laboratory bioassays. The most virulent EPN and EPF isolates were applied, in combination, to determine their interaction-effect on the mortality of BFW in the laboratory, as the final objective. In total, 70 soil samples were collected from deciduous fruit orchards and vineyards in the Western Cape. The soil samples were baited with mealworms, Tenebrio molitor (Coleoptera: Tenebrionidae) to trap EPNs and EPF, which were characterised by using morphological and molecular techniques, and evaluated for their potential to control the BFW adults. EPNs were isolated from 17 % (12) of the samples, with Heterorhabditis bacteriophora Poinar and Heterorhabditis safricana as the only two EPN species isolated. Heterorhabditis bacteriophora (53 % mortality) resulted in significantly higher (p < 0.05) mortality of adult BFW, compared to H. safricana (37 % mortality), in laboratory trials. EPF were trapped from 37 % (26) of samples, consisting of a total of 14 Beauveria bassiana isolates and 12 isolates from the Metarhizium anisopliae complex. A Metarhizium isolate (79 % mortality) resulted in significantly higher (p < 0.05) mortality of BFW adults, compared to B. bassiana (63 % mortality) in laboratory trials. Results obtained from the study indicate that the soil samples from the deciduous fruit orchards and vineyards from the Western Cape contained both EPNs and EPF that can be used to control BFW. Different EPN species were evaluated by laboratory screening for virulence against the different life stages of the BFW. A field trial to determine the performance of Steinernema yirgalemense, applied at different concentrations, followed. Results from a probit analysis showed S. yirgalemense to be six times more potent than Heterorhabditis noenieputensis, giving 95 % mortality of BFW larvae at a concentration of 400 infective juveniles (IJ) per insect, which was significantly higher (p < 0.05) compared to other concentrations. At a concentration of 100 IJs/insect, Steinernema yirgalemense, H. noenieputensis, and Steinernema feltiae resulted in significantly higher (p < 0.05) mortality of BFW larvae compared to the other EPNs, with no significant difference between each other. Heterorhabditis indica (70 % mortality) and H. baujardi (67 % mortality) resulted in significantly higher (p < 0.05) mortality of the BFW pupae, compared to H. noenieputensis (55 % mortality). In the case of adult BFW, Heterorhabditis indica (95 % mortality) and S. yirgalemense (94 % mortality) gave significantly (p < 0.05) higher mortality, compared to three other EPN species evaluated. In the field trials, S. yirgalemense, at 20 and 40 IJs/cm2, gave 69 % and 78 % mortality of BFW larvae, respectively. The results showed that all EPNs screened controlled the juvenile and adults stages of BFW. Steinernema yirgalemense was also shown to be capable of controlling BFW under field conditions, even at low concentrations. Different Different EPF isolates were tested at 1 × 106 conidia ml-1 for their virulence against the different life stages of the BFW. Results showed that Broadband® (Beauveria bassiana strain PPRI5339) (97 %) and Meta 69 (Metarhizium anisopliae) (93 %) gave significantly higher (p < 0.05) mortality of BFW larvae compared to Eco-Bb® (B. bassiana) (58 %), with no significant difference in mortality between Broadband® and Meta 69. In the case of pupae, Broadband® (92 %) gave significantly higher (p < 0.05) mortality, compared to Eco-Bb® (67.5 % mortality) and Meta 69 (65.8 % mortality). Broadband® (90 % mortality) gave significantly higher (p < 0.05) mortality of adult BFW compared to Eco-Bb® (69.2 % mortality) and Meta 69 (65 % mortality), of which neither differed from each other. When compared to a local EPF (M. anisopliae EA2), Broadband® (91.7 % mortality) gave significantly (p < 0.05) higher mortality of BFW adults, compared to EcoBb® (65 % mortality), Meta 69 (59.5 % mortality) and M. anisopliae isolate EA2 (64.2 % mortality), which did not differ significantly from one another. In a sand bioassay, Broadband® (85 % mortality) resulted in significantly (p < 0.05) higher mortality of BFW larvae compared to Eco-Bb® (55 % mortality) and Meta 69 (70 % mortality). The results indicated that all the EPF isolates tested were effective against juvenile and adults stages of the BFW, with Broadband® showing the most promise in controlling the BFW under laboratory conditions. The last objective of the study was to evaluate the combined use of the EPF; Eco-Bb®, Broadband®, Meta 69 and a local isolate M. anisopliae EA2, with the EPN, S. yirgalemense against BFW larvae and adults. The EPF were either applied alone, or at the same time as S. yirgalemense, or S. yirgalemense was introduced 1 and 2 weeks after fungal application; the EPNs were also applied alone. Results showed that 100% larval and adult mortality was obtained when S. yirgalemense was applied 1 or 2 weeks after Eco-Bb® and BroadBand® application. Synergistic interactions were noted when Eco-Bb® and S. yirgalemense, BroadBand® and S. yirgalemense, Meta 69 and S. yirgalemense, and M. anisopliae isolate EA2 and S. yirgalemense when applied 1 or 2 weeks after application of the EPF. Additive interactions were observed when the EPF and S. yirgalemense were applied simultaneously. Future research into the biological control of the BFW, using EPNs and EPF, should be focused on conducting large-scale field trials to demonstrate their potential use as biocontrol agents, within an integrated pest management programme. Both entomopathogens have shown outstanding potential to control the BFW when used alone, and in combination, could provide an economically viable control strategy against the BFW.
Biological control of two sporadic grapevine pests, Plangia graminea and Lobesia vanillana, using entomopathogenic nematodes.
(2019-03) Du Preez, Francois; Addison, Pia; Malan, Antoinette P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Plangia graminea (Serville) (Orthoptera: Tettigoniidae) and Lobesia vanillana (De Joannis) (Lepidoptera: Tortricidae) are two sporadic, minor pests of wine grape vineyards in the Western Cape province of South Africa. Recent years have seen an increase in their abundance and damage, which necessitates their control. Little is known about the biology, ecology and distribution of these insects. The aim of this study was to collect their basic ecological data and to evaluate entomopathogenic nematodes (EPN) as potential biocontrol agents. Nymphs of P. graminea were evaluated against 12 in vivo-cultured EPN species, of which Heterorhabditis zealandica (SF41), H. indica (SGS), Steinernema jeffreyense (J192), S. yirgalemense (157-C) and H. baujardi (MT19), resulted in > 82 % mortality after 48 h. Larvae of L. vanillana were evaluated against S. jeffreyense (J192) and S. yirgalemense (157-C), sourced from both in vivo and in vitro-cultures of the same isolates. Results show that they were susceptible to all treatments, resulting in > 72% mortality, and that there was no significant difference in mortality between in vivo and in vitro-cultured nematodes of the same EPN species, but that in the in vitro-culture, S. yirgalemense (98%) performed significantly better than S. jeffreyense (73%). Cadavers from screening bioassays were dissected to evaluate the presence of infective juveniles (IJ), which in turn confirmed insect mortality by EPN infection. The ability of IJs to complete their lifecycle in vivo, and their ability to produce a new cohort of IJs, suggests that they may be able to provide persistent control in favourable environments. Observations on the biology and ecology of P. graminea in grapevine, suggests that they do not have a soil stage and only a single generation per year. Plangia graminea were mainly reported from the Cape Winelands region in the Western Cape province of South Africa, from where they were collected in an attempt to establish a laboratory colony. They did not perform well in captivity, therefore field collected individuals had to be used in laboratory bioassays. Observations on L. vanillana suggests that this species also does not have a soil stage. They seem to have a generational life cycle of 4-5 weeks and to overwinter as pupae. Lobesia vanillana was successfully reared from field-collected larvae using an agar-based modified codling moth diet. The present study contributes to new knowledge of P. graminea and L. vanillana, and indicates that EPNs are promising as biological control agents when considered as part of an integrated pest management program.
Biology and ecology of the false codling moth, Thaumatotibia leucotreta (Meyrick)
(Stellenbosch : Stellenbosch University, 2013-12) De Jager, Zoe Marthalise; Addison, Pia; Terblanche, J. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Thaumatotibia leucotreta, the false codling moth (FCM), is a phytosanitary pest in South Africa posing a substantial threat to many of the country’s international export markets. Its pest status is of high importance because it has a wide ecological range and has been reported in all areas where citrus is produced in South Africa. Many methods of control have been implemented, such as chemical and cultural control, mating disruption and sterile insect releases. There was a need to obtain a more accurate understanding of FCM biology on deciduous fruit in South Africa and this then us to pose the questions described in the chapters to follow. The first aim was focused on the possibility of FCM diapause during winter. If FCM were to undergo diapause this could pose further problems for control methods, but knowledge thereof could also assist in more accurate and timely control methods. Considering past research on other Lepidoptera species, four physiological traits were chosen as indicative of a diapause state. Water loss rate, metabolic rate and the supercooling points should be lower if the individuals were in a diapause state, with a higher fat content expected for these individuals. Diapause induction was attempted through a gradual lowering of the environmental temperature in combination with longer nights to simulate overwintering conditions. Diapause was not observed in these experimental individuals. The second aim was to better understand the field biology of FCM. This was studied through in-field flight ability studies and damage assessments on four fruit kinds. Six release dates were used to measure the flight ability. The highest recapture rates were at minimum temperatures above 16°C and maximum temperatures averaging above 30°C, although the recapture rates were not significant in relation to the amount released. The recapture rates in the different fruit kinds were not significantly different, with the amount recaptured at the closest distance of 30 m being significantly more than that of the other distances. This was also only for the last release at the warmest temperatures. Fruit damage assessments were conducted and we were able to rear wild FCM from Granny smith apples, Forelle pears, Larry Ann plums and Satsuma and Clementine citrus cultivars. Citrus infestations had the highest count and a prolonged occurrence compared to the other varieties, due to its later harvest period. The third aim was to study the developmental parameters of FCM in different fruit kinds and an artificial medium. Firstly, FCM did not infest apples, Royal Gala and Pink lady’s, under laboratory conditions. Results were obtained using Forelle pears, Clementines and Thompson seedless grapes. On average the grapes had the shortest FCM developmental time from egg to adult stage, followed by oranges and then pears. Pears had the lowest developmental success rate, with that of oranges and grapes being much higher. Infestations took place at the stalk end of the fruit for the grapes and oranges, with the pears being infested at the calyx end. Future research should include an in-field life cycle, to determine the life cycle of FCM on different economically important fruit kinds under field conditions. The focus could also be shifted to where FCM overwinter, leading to better preventative control leading to lower infestation pressure during harvest periods. This is of utmost importance in an environment where maximum residue levels for pesticides dictate market access.
Characterisation of nematode symbiotic bacteria and the in vitro liquid culture of Heterorhabditis zealandica and Steinernema yirgalemense
(Stellenbosch : Stellenbosch University, 2013-03) Ferreira, Tiarin; Malan, Antoinette P.; Addison, Pia; Addison, M. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Entomopathogenic nematodes have the potential to be outstanding biocontrol agents against agricultural pest insects. Combined with their bacterial symbionts, these biocontrol agents have proven to be very effective against numerous pests. The nematodes belong to the families Steinernematidae and Heterorhabditidae, and are ideal to be used in, and integrated with, pest management systems. There is a dire need for new and innovative methods to control agricultural pests, as numerous pest insects have developed resistance against broad-spectrum insecticides. Together with the environmental impact of these insecticides and the safety aspect regarding humans and animals, the need to develop new technologies, including entomopathogenic nematodes for pest management, is high. In this study, the associated symbiotic bacteria of three entomopathogenic nematodes species were isolated, and the potential of two nematode species to be successfully mass cultured in liquid medium was evaluated. Regarding the symbiotic bacteria, results from the study showed that bacteria species from all three nematode species, Heterorhabditis noenieputensis, Steinernema khoisanae and Heterorhabditis zealandica, were novel. Heterorhabditis noenieputensis was isolated in the Mpumalanga province during a previous survey conducted in citrus orchards. The bacterium isolated from this nematode belongs to the genus Photorhabdus, and bear closest similarity (98.6%) to the type strain of P. luminescens subsp laumondii (TT01T). Photorhabdus luminescens subsp. noenieputensis subsp. nov., derives its name from the area where the nematode was sourced, namely the farm Springbokvlei, near the settlement Noenieput close to the Namibian border. Thus far, 85 Steinernema spp. have been described worldwide, including S. khoisanae which was isolated in the Western Cape province of South Africa. Four S. khoisanae strains, namely SF87, SF80, SF362 and 106-C, were used for characterisating the new bacteria from different localities in South Africa. Using the neighbor-joining method, all the strains were aligned with 97% homology to the 16S rRNA sequences of several Xenorhabdus- type strains, indicating that they belonged to the same genus. The multigene approach was used to distinguish between the Xenorhabdus spp. and partial recA, dnaN, gltX, gyrB and infB gene sequences of the various strains were analysed. The bacterium species was named Xenorhabdus khoisanae sp. nov. after the nematode from which it was isolated. The results showed that the third bacterium species, which was isolated from H. zealandica, was new. The sequence of the bacteria strain clustered with the type strains of P. temperata and P. asymbiotica, indicate that it belonged to the genus Photorhabdus. This is the first study to show that H. zealandica associates with a luminescent Photorhabdus species, rather than with the known non-luminescent P. temperata. The potential of H. zealandica and Steinernema yirgalemense mass culture in liquid was investigated. Results illustrated that H. zealandica and its P. luminescens symbiont can be successfully cultured in liquid. However, two generations occurred during the process time, instead of the desirable one-generation. The growth curve of the symbiotic bacteria during the process time was measured, in order to determine when the stationary phase was reached, with the results showing this to occur after 36 h. Therefore, the optimum amount of time required for inoculating the IJs and for aiding in maximum infective juvenile (IJ) recovery is 36 h for adding the nematodes post pre-culturing of the bacteria. Future research goals should be to increase the percentage recovery in liquid culture, which would increase the number of nematodes produced per ml, which would, therefore, reduce the processing time significantly. The results from mass culturing the second nematode species, S. yirgalemense, indicated an asynchronous nematode development in the first generation. Growth curves were performed with the symbiotic bacteria that showed the exponential phase of Xenorhabdus started after 15 h, and that, after 42 h, the stationary phase was reached, with an average of 51 × 107 cfu·ml-1. Bioassays were performed to compare the virulence between in vitro- and in vivo-produced nematodes, with the results showing that the in vitro-produced nematodes were significantly less virulent than were the nematodes produced in vivo. The success obtained with the production of S. yirgalemense in liquid culture can serve as the first step in the optimising and upscaling of the commercial production of nematodes in industrial fermenters. The last aim of the current study was to determine when Xenorhabdus reached the stationary phase, when it is grown in a 20-L fermenter, as this would be the optimum time at which to add the IJs of S. yirgalemense. Such characteristics as the effect of stationary phase conditions on the bacterial cell density and on the DO2 rate in the fermenter were investigated. The results showed that the stationary phase of Xenorhabdus was reached after 36 h at 30˚C, which took 6 h less than did the same procedures followed with the Xenorhabdus sp. cultured in Erlenmeyer flasks on orbital shakers. This is the first step toward the liquid mass culturing of S. yirgalemense in industrial-size fermenters. Data from this study indicated the optimum amount of time that is required for adding nematodes to the bacterial culture in the fermenter, and for ensuring the optimum recovery of IJs, as well as a subsequent high yield of nematodes within a minimum processing time. This is the first report of its kind to investigate comprehensively the successful liquid culture of two South African entomopathogenic nematode species for the sole purpose of evaluating potential commercialisation. Results emanating from this study could be used as groundwork in future, in combination with similar research such as culturing nematodes intensively in large fermenters.
Chemical ecology and eco-physiology of the grain chinch bug, Macchiademus diplopterus (Distant) (Hemiptera: Lygaeidae: Blissidae), a phytosanitary pest of South African export fruit
(Stellenbosch : Stellenbosch University, 2012-03) Okosun, Olabimpe Olayem; Johnson, Shelley; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The grain chinch bug, Macchiademus diplopterus, is an endemic pest of cultivated grain crops and wild grasses in the south-western Cape region of South Africa. In early summer when host plants dry out, adult grain chinch bugs aggregate in large numbers in shelter sites in surrounding areas and enter into aestivation. These shelter sites sometimes include the stalk or calyx ends of fruit, and shelter-seeking bugs can also contaminate export fruit cartons, consequently posing a phytosanitary/quarantine risk to importing countries. Presently, there are no feasible pre- or post-harvest control measures to manage this quarantine risk. The aggregating behaviour of grain chinch bugs suggests the involvement of pheromones. Therefore, investigating the chemical ecology of grain chinch bugs for potential use in control measures is the focus of the first research chapter of this study. Gas chromatography-mass spectrometry (GC-MS) was used to identify headspace volatiles collected from aggregating bugs. Olfactometer bioassays were conducted to assess the attractiveness of each gender to separate sexes, individual compounds and a mixture of the compounds as a formulated lure. The lure was tested in field trapping trials with delta and bucket traps. In the bioassays with the live insects the response of each gender to live females was greater than the responses of each gender to live males, suggesting that females may disseminate the pheromones more efficiently than males. The following eight volatile compounds were indentified from the GC-MS analysis: hexanal, (E)-2-hexenal, (E)-2-hexenol, (E)-2-hexenyl acetate, (E)-2-octenal, (E)-2-octenol, (E)-2-octenyl acetate and tridecane. In the bioassays with individual compounds, three of these eight compounds, hexanal, (E)-2-hexenal, and tridecane, elicited attraction of both females and males. The formulated lure was attractive to both males and females in the laboratory bioassay, but this attraction was not evident in the field. In the field, there was only one occasion when a significantly higher number of bugs were caught in baited traps compared to unbaited traps. Trap catches were very low compared to the actual level of infestation in the field which was evident from corrugated cardboard bands tied around tree trunks which contained many sheltering bugs. The low trap catches seen in the field were partly due to competition between the synthetic pheromone lure and the natural pheromones emitted by aggregating live insects. Also, the characteristic shelter-seeking behaviour of grain chinch bugs influenced trap catches, as more bugs were found in places that provide shelter, like cardboard bands and walls of the delta traps. This behavior of aestivating bugs could be used to the advantage of trapping bugs by integrating sheltering sites into traps in future trials. Also, the lure needs to be improved for optimum efficiency in the field. The second research chapter also addresses the quarantine risk posed by grain chinch bugs, by investigating the thermal biology of bugs to ultimately facilitate the development of effective post-harvest treatments. Critical thermal minimum and maximum temperatures (CTmin and CTmax) of both active and aestivating bugs were subjected to critical thermal limits analysis. The CTmin and CTmax of aestivating bugs were not affected by gender (p > 0.05). There was a decrease in CTmin from the active period into aestivation for both males (2.8°C to 1.0°C (± 0.1)) and females (2.1°C to 0.6°C (± 0.1)). Also, for CTmax there was an increase in tolerance from the active period into the aestivation period for both males (49.9°C to 51.0°C (± 0.1)) and females (49.9°C to 51.5°C (± 0.1)). To determine the plasticity of grain chinch bug thermal tolerance, aestivating bugs at 27 weeks into aestivation, were acclimated at different temperatures and photoperiods [18°C (10L:14D) and 26°C (16L:8D)] for a period of seven days. Both low (18°C) and high (26°C) acclimation temperatures and photoperiods increased CTmin of aestivating grain chinch bugs at 14 weeks from 0.8°C to -1.2°C and -0.1°C (± 0.1) respectively. However, CTmax was not altered by acclimation temperatures (p > 0.82). Field temperatures at collection sites were recorded to compare to grain chinch bugs thermal tolerance levels exhibited in the laboratory. These results, as well as the effects of acclimation treatments on the CTmin of bugs, have implications for post-harvest treatments, and understanding the quarantine risk posed to importing countries. The information generated from this study can be used to further advance the development of both effective pre-harvest and post-harvest control measures to reduce grain chinch bug quarantine risk.
Determining the quality of mass reared male codling moth, Cydia pomonella (Lepidoptera: Tortricidae), by assessing flight performance under laboratory, semi-field and field conditions.
(Stellenbosch : Stellenbosch University, 2016-03) Visser, Andri; Addison, Matthew; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology
ENGLISH ABSTRACT: The codling moth, Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the insect pest that poses the greatest threat to the South African pome fruit industry. Traditionally, insecticides have been used to control this pest, but recently these chemicals have failed to adequately suppress codling moth due to the build-up of resistance in populations. Along with the added pressure from export markets to reduce insecticide residues, the need for feasible control alternatives has never been greater. The Sterile Insect Technique (SIT) is an environmentally friendly control method that has had great success with the control of a number of different insect pests, including codling moth. The technique involves the mass production and release of sterile insects with the goal of over-flooding the natural population, but it is also crucial that the mass reared insects can successfully compete for mating opportunities. However, no comprehensive quality control assessment method currently exists for mass reared codling moth. This study aimed to identify and develop laboratory, semi-field and field methods that can be used to assess the quality of mass reared codling moth. This would be accomplished by developing flight performance assessments that could be used to distinguish between mass reared moths of high and low quality. The experiments conducted for each assessment method compared the flight performance of moths subjected to different treatments of radiation dose, ageing and handling during transport. For the laboratory quality control assessment, a matrix of nine flight cylinders with combinations of three heights (2.5, 15 and 26.5 cm) and three diameters (10, 14 and 16 cm) was developed which compared the escape rate from these cylinders of moths subjected to different treatments. The semi-field assessment (conducted in a horticultural tunnel) measured the arrival time of the moths subjected to different treatments at a trap 12 m from the point of release. Field release/recapture assessments were conducted at two apple orchards in Elgin (one covered with netting and one uncovered), as well as an uncovered pear orchard in Stellenbosch. The flight performance of mass reared moths was determined by evaluating their dispersal rate from a central point of release with a trapping grid of eight pheromone baited delta traps. The efficacy of the three assessment methods was also evaluated for mass reared false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), in separate experiments. Results indicated that increasing radiation dose had a detrimental effect on moth quality, but no effect could be observed for the age treatments. The effect of bran handling on moth quality could be observed in the field only, suggesting that it is dependent on the time period the moths are transported in the bran. The flight cylinder method was able to accurately indicate of the quality of moths as it relates to flight performance, but that the field assessments were the best indication the overall competitiveness in the field. This was true for both codling moth and false codling moth. The semi-field assessment method was not successful at distinguishing between moths of different quality; the development of an effective semi-field quality test is therefore still on-going.
Developing an integrated management system for western flower thrips, Frankliniella occidentalis (Pergande), on deciduous fruit, using semiochemicals in a push-pull strategy
(Stellenbosch : Stellenbosch University, 2016-12) Allsopp, Elleunorah; Addison, Pia; Dewhirst, Sarah Y.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Western flower thrips (WFT), Frankliniella occidentalis (Pergande), causes both feeding (russetting and silvering) and oviposition (pansy spot) damage to fruit. Despite routine insecticide applications from 20% bloom until petal fall, pansy spot and pitting damage was still being reported, particularly on plums. This study was initiated to determine the reason for the apparent failure of chemical control and the cause of pitting damage, and to investigate the feasibility of developing a push-pull system to minimize economic WFT damage by using deterrent plant essential oils and trap crops. Field trials in commercial plum orchards in the Western Cape confirmed that WFT oviposition causes pitting damage. The apparent failure of insecticide applications to prevent pansy spot and pitting damage was due to the fact that WFT entered plum blossoms even before the petals opened, where they were protected from contact insecticides applied at 20% bloom. No treatment threshold could be determined because no consistent significant relationship was found between blue sticky trap counts and WFT oviposition damage to plums. Sticky trap counts thus only serve to indicate presence or absence of WFT in an orchard. To reduce WFT oviposition damage, monitoring must start as soon as flower buds begin to swell, some blue sticky traps should be hung closer to the ground during the early season and, if WFT are present, the first spray application should be made as soon as blossoms reach balloon stage. To provide the “push” in a push-pull system, the potential of three plant essential oils to reduce WFT oviposition rate on plum blossoms was investigated. This study was the first to demonstrate that suspensions of thymol (10%), methyl salicylate (1% and 10%) and carvacrol (1% and 5%) significantly reduced WFT oviposition rate when applied to individual plum blossoms in laboratory bioassays. Significant results could not be obtained in semi-field trials using potted plum trees, mainly because the suspensions were unable to provide sustained release of the volatile essential oils at behaviourally effective concentrations. Phytotoxic damage to blossoms was encountered at higher concentrations of the essential oils. While thymol, methyl salicylate and carvacrol were shown to have potential as oviposition deterrents for WFT on plum blossoms, they could only be considered for commercial use if stable suspensions can be developed to deliver sustained release of behaviourally effective concentrations with no phytotoxic effects. An effective trap crop that provides the “pull” should be as attractive, or more attractive to WFT than plum blossoms. White clover, Trifolium repens L., was selected for investigation. The attractiveness of flower volatiles of clover flowers and plum blossoms, collected by means of air entrainment, was evaluated using a Y-tube glass olfactometer. Results showed that the volatiles of clover flowers and plum blossoms are both very attractive to WFT females. White clover shows potential as a trap crop for WFT, but a control system on heavily infested clover should be implemented to remove WFT and clover flowers should be cut before honeybees are brought in to ensure effective pollination. This study provided crucial information to improve the efficacy of early-season chemical control of WFT. Three essential oils were identified as potential oviposition deterrents for WFT on plum blossoms and white clover was identified as a potential trap crop. Development of suitable formulations of the essential oils is required before a push-pull system to manage WFT more sustainably in deciduous fruit orchards can be implemented.
Development of a habitat management plan for improving the biological control of the vine mealybug planococccus ficus (signoret) in vineyards
(Stellenbosch : Stellenbosch Univerisity, 2015-03) Faure, Sariana; Addison, Pia; Veldtman, Ruan; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH SUMMARY: The vine mealybug, Planococcus ficus (Signoret) is a major, cosmopolitan pest in all regions where grapes are grown. Vine mealybug has a direct injurious effect on vines through feeding, produces honeydew, on which sooty mould develops and has been shown to be a vector of the grapevine leafroll virus and associated closteroviruses. This project entailed research on the parasitoids of P. ficus, mainly Coccidoxenoides perminutus (Timberlake). The aim of this work was to contribute basic biological information for the establishment of a habitat management plan in vineyards to improve biocontrol of P. ficus. Two surveys were conducted to determine, firstly, the occurrence of mealybug parasitoids in the vineyards and their associated natural habitats, and secondly the association between flowering plants and parasitoids close to vineyards. Olfactometer screenings were conducted to determine attractiveness of six plants as food sources for adult C. perminutus. A comprehensive life history experiment was initiated to be compared with previous findings. In the first survey, to assess the biodiversity of mealybug parasitoids in vineyards and their associated natural habitats, C. perminutus, Anagyrus sp. near pseudococci (Girault) and Leptomastix dactylopii (Howard) were the predominant parasitoids found between January and May, with a peak in abundance during February. Signficantly more parasitoids were found in vineyards compared to associated natural habitats (p=0.049). The survey further indicated that these parasitoids, being density-independent and therefore not in need of high pest populations to sustain numbers, could contribute to integrated pest management, and with effective habitat modifications, their numbers could be naturally boosted to lend a valuable eco-system service. In the second survey, to determine whether parasitoids occur in the field in flowering plants associated with vineyards, a total of 20 indivdual parasitoids from 16 species were found. This is a promising indication that, although their impact on P.ficus was not measured during this study, the correct flowering plants interplanted in vineyards or on the edges could have a positive effect on the necessary occurrence of mealybug parasitoids as well as other natural enemies and pests in vineyards. Attractiveness of plants for C. perminutus was determined through the screening of a variety of flowering plants with a four-armed Pettersson olfactometer. Of the six plants tested, only Euryops abrotanifolia (L.) DC had a significant attractant effect (p=0.003926) on C. perminutus. The population of the parasitoid could possibly be increased by planting this plant in or around vineyards to provide a food source, and it is recommended that this plant be further investigated as a parasitoid attractant in the field. Furthermore, more plants need to be tested for inclusion in habitat management, as it is likely that a combination of plants will be more effective for biological control. To determine life table parameters of C. perminutus, including adult fitness and larval host preferences, laboratory experiments were conducted at 25°C on Planococcus citri (Risso), as initial experiments utilizing P. ficus had failed. In constrast with previous studies where the second and third nymphal instars were parasitised, all nymphal instars were attacked in this study, with no significant difference between them (p=0.057). Cost of life when laying eggs or not also came to no significant difference (p=0.46252). Lifetable parameters (Ro=159.5; T=27.602; rm=0.511) were different to those determined by Walton (2003) (Ro=69.94; T=29.5; rm=0.149) except for T which was similar, although the latter study was conducted on P. ficus. These differences could also be attributed to the use of mummies instead of hatched parasitoids, when collecting progeny for the determination of the preferences and parameters. Information obtained through these above mentioned experiments should be of use to rearing facilities and contribute to the establishment of a habitat management plan in vineyards to improve the control of P. ficus.
The development of a management strategy for the control of the Cape grapevine leafminer, Holocacista capensis (Lepidoptera: Heliozelidae), in South African table grape vineyards
(Stellenbosch : Stellenbosch University, 2019-03) Steyn, Leigh Ami Isbell; Addison, Pia; Malan, Antoinette P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The Cape grapevine leafminer, Holocacista capensis Van Nieukerken & Geertsema (Lepidoptera: Heliozelidae) has become a common pest on table grapes and wine grapes in the Western Cape province of South Africa, since it was first reported in 2012. The presence of cocoon casings on grape bunches intended for export makes them a pest of economic importance, although its recognised pest status does not reflect the severity of some of the infestations that have occurred in the Berg River region. To date, control strategies have consisted of insecticide applications or manual, labour intensive post-harvest removal of rooted cocoon casings from table grape bunches during the packing process. To aid in the development of an integrated pest management (IPM) strategy, this study focused on understanding aspects of cultural, chemical and biological control strategies, whilst considering genetic diversity and environmental variables that influence H. capensis populations. In agreement with other studies conducted on problematic leafminers, field trials indicated that ambient light intensity, climatic conditions and plant nutrient composition affected H. capensis populations in commercial vineyards. Correlations derived from the evaluation of temporal satellite imagery to determine the normalized difference vegetation index (NDVI), indicated the potential for the use of this technology for monitoring leafminer invasions in the future. A preliminary study on the genetics of the pest involved the extraction of DNA from 52 male moths collected from commercial vineyards and natural forests (using baited Delta traps) in and around the Western Cape. The study was able to confirm species identity and synonymy of the insects collected from field-placed traps. An insecticide screening trial, conducted in the laboratory using varying doses of a variety of commercially available insecticides, identified spinetoram (spinosyn), dichlorvos (organophosphate) and cypermethrin (pyrethoid) as good candidates for inclusion in an IPM strategy. High mortality (> 87%) was recorded at the lowest doses (a quarter of the recommended field dose). Entomopathogenic nematodes (EPNs) were screened in the laboratory as an alternative to a management strategy focused solely on the use of chemical applications. Using a 200 infective juvenile (IJ)/50 µl of distilled water solution, EPNs were able to penetrate leaf galleries (mines) and cause larval mortality. Three EPNs, Heterorhabditis baujardi Phan, Subbotin, Nyugen & Moens, Heterorhabditis indica Poinar, Karunakar & David and Heterorhabditis noenieputensis Malan, Knoetze & Tiedt, were able to cause > 86% mortality of leaf-mining larvae and have the potential to be adopted in an IPM strategy against H. capensis. The use of bunch covers as a physical control strategy was tested in the field, for cases where leafminer infestations are unavoidable and maximum residue limits (MRLs) have been reached, to preclude insecticide treatments. All covers tested proved to successfully reduce the presence of rooted cocoon casings on bunches. This study has provided a positive forecast for the success of future chemical and biological applications and has provided the groundwork for the development of an IPM strategy against H. capensis on grapevines.
Development of handling and transport protocols for Eldana saccharina (Lepidoptera: Pyralidae) sterile insect technique (SIT) programme
(Stellenbosch : Stellenbosch University, 2021-04) Serfontein, Adriaan Jacobus; Conlong, D. E.; Addison, Pia; Desmond, Edward; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Eldana saccharina Walker (Lepidoptera: Pyralidae), is indigenous to sub-Saharan Africa and is a serious economical pest of sugarcane in South Africa. Recent area-wide integrated pest management (AW-IPM) efforts have proven to be effective in lowering infestations and better predicting population growth and spread into new areas. The sterile insect technique (SIT) promises to provide great benefit as a component of the AW-IPM strategy. This study aimed to establish parameters for collection, packaging, and transport of recently emerged E. saccharina adult males, within a maintained cold chain conjointly with methodologies for the routine assessment of the performance and competitiveness of sterilized insects. These treatments should not impact the fitness nor mating ability of the adults exposed to them. Several major outcomes were realized, summarized as follows: Parental male and female pairs exposed to 100 Gy irradiation prior to mating provided an 83.3 % male biased first filial generation. Thus, a male biased, semi sterile generation could be reared for collection and release using this technique; difference between average male (0.0700 g) and female (0.133 g) pupal weights (as an indication of adult weight) were identified as a morphological trait that could be exploited to obtain a high degree of sex separation; and the plenum collection box was effective in collecting male and female adult E. saccharina (a mean of 80.67 % ± 4.56 % adults were collected when placing 200 adult moths (male : female = 1:1) into the prototype collection system overnight for 12 hours replicated three times). Furthermore, the effect of exposure of virgin E. saccharina males to 5 °C for 24, 48 and 72 hours on male mating frequency and longevity was measured to determine the impact of prolonged periods of cold exposure to male fitness. The 72 hour treatment showed a significant decrease in male mating frequency (average of 4.4 females mated at 48 h versus 2.7 females mated at 72 hours). It is therefore possible to hold E. saccharina at 5 °C for 48-hours without impacting on moth fitness in terms of mating frequency. Bran was identified as a good temperature insulating material to use as a packaging substrate for adult males, as it buffered temperature fluctuations over time inside a transportable freezer set at 5 °C (1.5 °C to 5.5 °C) when fully stocked with bran, versus being empty (0 °C to 6 °C). Bran’s effect as a packaging substrate on male fitness during high density packaging and exposure to 5 °C for 24, 48 and 72 hours showed no significant decrease in male mating frequency (mean mating frequency of 2.8889 females mated). Males did have a decreased mating frequency (1.4667 females mated) after 72 hours for the no bran packaged adults. A visual rating system was tested to measure the difference in loose scale cover - on the eyes, dorsal surface, ventral surface, as well as scale loss from the pronotum - between bran and no bran packaged moths. There was a clear improved visual quality with bran packaged adults compared to no bran packaged adults with less scale loss from the pronotum and less loose scales covering the eyes and ventral and dorsal surfaces, indicating that this visual rating system could be valuable as a quality control check at the point of elease.
The diversity and ecology of mites (acari) in vineyards
(Stellenbosch : Stellenbosch University, 2019-03) Vermaak, Mia; Addison, Pia; Veldtman, Ruan; Ueckermann, Eddie; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The common grapevine (Vitis vinifera L.) is the main species used for wine making, with South Africa being one of the top wine exporting countries. Grapevine is vulnerable to a range of pests, one of these being mites. Plant-parasitic mites are extremely damaging pests with a rapid generation time, high fecundity and a tendency to over-exploit their hosts. Disconcertingly, the diversity of mites in vineyards in South Africa is virtually unknown. Surveys have been done with predatory mites and phytophagous mites being recorded, but no recent studies focussing on their ecology, pest status and seasonal cycles have been collected. The aim of this study was to survey phytophagous and predatory mite diversity and to investigate pest status of the plant feeding mites of South African grapevine, including the recently introduced, invasive Brevipalpus lewisi. Sampling was done over a two-year period and included four conventional farms and one organic farm found in the Winelands region of the south Western Cape, South Africa. Each conventional farm contained a motherblock, nursery and commercial vineyard while the organic vineyard only consisted of a commercial vineyard. At each site vine branches were collected on a regular basis from November 2016 to April 2018. During the winter months weed and cover crop samples were also collected at the conventional farms. Mites were collected from vine leaves with a mite brushing machine. Weeds and cover crops were inspected with a microscope and mites were collected from them with a fine brush. Mites were slide mounted and identified. The predatory mite diversity from plant samples was much higher than expected. Eueseius addoensis and Typhlodromus praeacutus were the most abundant predatory mites found in the commercial vineyards and nursery material with T. praeacutus and Neoseiulus barkeri the most common in motherblocks. Brevipalpus species were the abundant phytophagous mites, with Tetranychidae being less abundant. Brevipalpus lewisi was the most dominant species. It did not cause any visual symptoms of damage on the vine. Brevipalpus lewisi did not seem to have natural enemies that were at sufficient densities to affect any control. The seasonal cycles for the predatory and phytophagous mites were established over a period of two seasons; from November 2016 to May 2017 and from November 2017 to April 2018. In commercial vineyards E. addoensis and T. praeacutus were the only predatory mites that were present throughout the entire season. The other predators were present for one or two months. Motherblocks and nurseries had sporadic occurrences of predators. In all three vineyard blocks B. lewisi was dominant throughout the seasons. The organic vineyard survey showed a high diversity of predatory mites and an absence of plant-feeding mites. The dominant predators were also E. addoensis and Typhlodromus saevus. In this study it was found that the main grapevine mites did not migrate to alternate hosts like the cover crops and weeds during winter. Mites that were found on both ground cover and vines were Tydeus grabouwi and Tetranychus ludeni. The findings of this study forms baseline data to develop management strategies to be used in the wine industry. Understanding the diversity and seasonal cycles of the mites occurring on grapevine will make for better decision making in pest control.
Diversity and ecology of phytophagous weevils in the deciduous fruit industry, South Africa
(Stellenbosch : Stellenbosch University, 2019-03) Magagula, Mxolisi Meshack; Addison, Pia; Addison, Matthew; Haran, Julien; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The banded fruit weevil, Phlyctinus callosus, Boheman, 1834 (Coleoptera: Curculionidae), is a serious and economically significant pest of apple orchards and vineyards in the Western Cape Province of South Africa. Adults can be accidentally packed with export fruit causing quarantine problems and is regarded as an international phytosanitary pest. A nine month population survey (during the fruiting season of September 2017 to May 2018) was conducted in three different fruit growing areas, namely; Stellenbosch, Ceres and Grabouw, Western Cape Province, South Africa, to determine the assemblage structure and an identification key was compiled for all weevils found in vineyards and apple orchards during this survey. Fortnightly monitoring using 15 cm cardboard bands (tied around the base of the trunk), has indicated that there were nine weevil species found to occur in apple orchards and vineyards, namely, Eremnus atratus (Sparrmann, 1785), Eremnus chevrolati Oberprieler, 1988, Eremnus occatus Boheman, 1843, Eremnus setifer Boheman, 1843, Naupactus leucoloma Boheman, 1840, Pantomorus cervinus (Boheman, 1840), Phlyctinus callosus Boheman, 1834, Sciobius tottus (Sparrmann, 1785) and Tanyrhynchus carinatus Boheman, 1836. Vineyards recorded the highest diversity with eight species recorded: T. carinatus, P. callosus, E. setifer, E. atratus, E. chevrolati, E. occatus, P. cervinus and N. leucoloma, whereas apple orchards recorded the lowest diversity with only four weevil species found: S. tottus, P. cervinus, E. atratus and P. callosus. E. occatus was collected for the first time in vineyards. All nine species belong to the sub-family Entiminae (root weevils). T. carinatus was found in low abundance and it is the only weevil species with a long rostrum and easier to distinguish from the rest of the weevils collected during the study. The rest of the weevils differ only slightly in morphology, especially the Eremnus. Based on collected species during the survey, an illustrated morphological key was produced with species identification information. DNA barcoding was supplied to provide a complementary diagnosis tool. Seasonal monitoring was undertaken to establish population peaks during the fruiting season, in relation to P. callosus, which was regarded as a key pest in apple orchards and vineyards. Furthermore, damage assessments were conducted by assessing fruit clusters or bunches and recording the percentage damage per block, first in early December (pre-thinning assessment) and later in early April (pre-harvest assessments). Weevils emerged in midOctober in vineyards and around late-October in apple orchards. A peak in adult populations were reached between November and December, after which the population dropped drastically from January up to May. P. callosus was the most abundant weevil species and it accounted for 82 % of all the weevils collected during the survey. Other weevils were found in lower abundance: E. occatus (5.9 %), E. setifer (5.8 %), E. chevrolati (2.1 %), P. cervinus (1.9 %), N. leucoloma (1.1 %), T. carinatus (0.4 %), S. tottus (0.3 %), and E .atratus (0.3 %). Most damage took place during the pre-thinning assessment and to a lesser extent in the preharvest assessment. Most of the damage in apple orchards and vineyards was attributed to P. callosus, based on Spearman’s rank correlations, with the remaining weevils contributing to some damage. As it is possible that certain soil physical parameters such as soil texture, soil chemistry and soil bulk density along with the presence of ground cover impact the population of weevils, soil samples were collected in early September, and analyzed for soil chemistry and soil texture. Groundcover surveys and identification took place every two weeks. The results indicated that there was no significant (P = 0.05) relationship between soil chemistry, soil bulk density, soil texture or ground cover percentage and weevil population. The association between adult P. callosus and groundcover was very weak. It is possible that other factors such as soil moisture, cultural practice within the ground cover, relative humidity and soil penetrability impact the weevil population in apple orchards and vineyards. This study identified and recognized nine weevil species causing damage in vineyards and apple orchards in the Western Cape Province, South Africa, of which one was recorded for the first time in vineyards, as well as assessing the effect of abiotic and biotic attributes towards the population of weevils on these crops. The findings of this study aimed towards supporting the development of ecologically-based control strategies; which enable further research into sustainable and integrated approaches to the management of these weevils.
Ecology and biocontrol options of the leaf miner, liriomyza huidobrensis, on potatoes in the Western Cape province
(Stellenbosch : Stellenbosch University, 2021-04) Mugala, Thabu; Addison, Pia; Malan, Antoinette P.; Visser, Diedrich; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The potato leaf miner, Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae), is a devastating pest of potatoes, worldwide. However, little knowledge of the biology and ecology of this pest in South Africa exists, with both factors being cardinal elements in implementing an effective integrated pest management (IPM) programme. Control of the pest relies on the extensive use of chemical insecticides. Concerns regarding insect resistance, human safety and environmental impacts have, however, encouraged the development and use of alternative environmental control strategies, including the use of entomopathogenic nematodes (EPNs) and fungi (EPF). The present study focuses on the population dynamics of L. huidobrensis during the winter and summer period, a parasitoid survey and biological control using EPNs and EPF. The study showed differences in adult leaf miner populations in both the potato fields and the natural vegetation for both the winter and summer monitoring periods. The abundance and population densities of leaf miners increased during summer, while being very low during the winter monitoring period. The observed trend was that the leaf miner populations increased during crop development, with damage regularly being spotted on the potato leaves two weeks after plant emergence. Five parasitoid species associated with L. huidobrensis were identified during the monitoring periods, with Diglyphus isaea being the most abundant species. After assessing the occurrence of entomopathogens in the soil samples collected from the potato fields, one EPN species Heterorhabditis zealandica, one insect-associated nematode Acrobeloides sp. and two EPF species, Metarhizium robertsii and Metarhizium majus were isolated from the 16 surveyed potato fields. Four EPN species were screened for pathogenicity against the larval and pupal stages using different concentrations of infective juveniles (IJs) in the laboratory, which included Heterorhabditis bacteriophora, Heterorhabditis baujardi and Steinernema yirgalemense and which were obtained from the collection of the Department of Conservation Ecology and Entomology, Stellenbosch University, with the fourth species Heterorhabditis zealandica being isolated from the potato fields. The pathogenicity results of all the EPNs at 200 IJs/50 μl of distilled water solution indicated insect mortality of > 40 % for both the leaf mining larvae and the pupae. However, pupae and larvae trials indicated that the best performing treatment was found to be H. baujardi with more than 57 % of pupae mortality and > 71 % larvae mortality. The findings, thus, indicate the EPNs potential for adoption as part of an IPM strategy. On the other hand, two different species of EPF, namely Metarhizium robertsii and Beauveria bassiana, were tested for pathogenicity against the pupae of the potato leaf miner. The EPF were able to cause 67 % mortality. The study also screened five different isolates of M. robertsii found during the monitoring period, with the results obtained indicating very high pupae mortality of more than 80 % of pupae. The study provided a positive forecast for the management of potentially damaging populations using entomopathogens as biocontrol agents against L. huidobrensis, in potato cultivation, in South Africa. This study was a laboratory assessment and thus a first step towards further development of a management strategy.
Efficacy of entomopathogenic nematodes and fungi as biological control agents of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) under South African conditions
(Stellenbosch : Stellenbosch University, 2016-03) Stokwe, Nomakholwa Faith; Malan, Antoinette P.; Addison, Pia; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann) is an important pest of apples, (Malus domestica Borkh.). Severe infestations by WAA can lead to colonies near spurs that can deposit honeydew on fruit, which serve as a substrate for sooty mould. If not controlled, it can lead to destruction of developing buds in the leaf axils and a reduction in tree vigour or formation of galls. Increasing interest in environmentally sustainable farming has increased the demand for environmentally friendly pest control methods. Therefore the use of naturally occurring biocontrol agents and more environmental friendly methods are needed. The study aims to determine the potential of entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) to control WAA. EPNs and EPF are naturally occurring and environmentally friendly microbials that have the potential to be developed into bio-pesticides. Research on the use of EPNs and EPF as biocontrol agents against E. lanigerum showed that they have potential to be used to control WAA. This is the first report on the use of EPNs and EPF to control WAA in South Africa. These findings are significant, especially to those interested in integrated pest management (IPM). The first objective of this study was to evaluate the virulence of endemic EPN species against WAA by conducting laboratory bioassays and to determine the effect of imidacloprid on the infectivity of EPNs. A total of seven entomopathogenic nematode isolates were evaluated for their potential as biological control agents for WAA in the laboratory, using a 24-well bioassay protocol screening method. From these, the two most virulent nematode isolates were selected. In all cases studied the degree of infection associated with mortality was less than 50% and the other tested nematode isolates were less successful. Although penetration, recovery of the non-feeding Infective Juveniles (IJ) to the feeding stage and development into the adult stage was observed in some cases, the nematodes failed to complete their life cycle inside the WAA. When this failure to develop and reproduce was investigated using direct screening with the associated symbiotic bacteria and insect extract, it became evident that the WAA haemolymph contains an inhibitory factor that prevented the symbiotic EPN bacteria from growing. WAA size was also shown to have an effect on insect mortality, with higher mortality observed in adults and low mortality for intermediates, while no mortality was observed for the crawlers. The two most virulent nematode isolates, Nguyen, Tesfamariam, Gozel, Gaugler & Adams, 2004 and Heterorhabditis zealandica Poinar, 1990 were not affected by the addition of imidacloprid, leading to the conclusion that EPNs and imidacloprid could potentially be applied as tank mix. The second objective of the study was to evaluate the use of two EPF, Beauveria bassiana and Metarhizium anisopliae, for the control of WAA in the laboratory. The five fungal isolates tested were pathogenic to WAA and they caused significant WAA mortality compared with the control. The commercial isolates Beauveria bassiana (Eco- Bb strain R444) and Metarhizium anisopliae (ICIPE 69) caused the highest rate of WAA mortality and were selected for further evaluation. When the effect of EPF concentration and exposure time of these two most virulent isolates were evaluated, it became evident that increased EPF concentration (1 × 107 to 1 × 1010 conidia ml-1) and exposure time increased WAA mortality. This lead to the conclusion that a relatively long incubation period and high EPF concentration are needed to achieve full efficacy of the these fungal isolates for controlling WAA. The third objective of the study was to evaluate the interaction between EPNs and EPF for the control of WAA and the effect of mulching on EPN efficacy in pot trials. Joint use of EPNs and EPF increased insect mortality when compared to treatments with only EPNs or only EPF, indicating an antagonistic effect. Combining S. yirgalamense with B. bassiana (Eco- Bb® strain R444) and M. anisopliae (ICIPE 69) provided no advantage for improved efficacy against WAA, which lead to the conclusion that M. anisopliae (ICIPE 69) or B. bassiana (Eco- Bb® strain R444) could be used for suppression of WAA. When the environment was manipulated by adding mulches, WAA mortality was slightly higher compared to the unmulched soil. However, these differences were not statistically significant. The fourth objective of the study was to evaluate the efficacy of S. yirgalamense, B. bassiana and M. anisopliae against WAA in the field. A single application of S. yirgalamense (80 IJs/cm2) B. bassiana (Eco- Bb® strain R444) (1g/L) and M. anisopliae (ICIPE 69) (200 ml/ha) effectively controlled WAA under South African field conditions. The EPF performed better than EPNs. Based on these results the success in controlling the root colonies resulted in greatly reduced infestations of the aerial parts of the apple trees in the trial. These studies attempted to determine if local EPNs and EPF are pathogenic to WAA and if they could be used to control it in the field. It was found that all the isolates tested were pathogenic to WAA in the laboratory and that S. yirgalamense, B. bassiana and M. anisopliae were the most effective isolates. They were able to control WAA under field conditions, although the degree of control was low. Therefore future studies should be designed to investigate the application and post-application conditions required for EPF to be effective with respect to WAA control and to ensure that the application of the fungi is economically viable. The role of the wetting agent in improving soil saturation, penetration and uptake of EPNs and EPF also requires to be investigated.
Entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of codling moth, Cydia pomonella (L.) under South African conditions
(Stellenbosch : Stellenbosch University, 2008-12) De Waal, Jeanne Yvonne; Addison, Pia; Malan, Antoinette P.; Addison, M. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
The codling moth, Cydia pomonella (L.), is a key pest in pome fruit orchards in South Africa. In the past, broad spectrum insecticides were predominantly used for the local control of this moth in orchards. Concerns over human safety, environmental impact, widespread dispersal of resistant populations of codling moth and sustainability of synthetic pesticide use have necessitated the development and use of alternative pest management technologies, products and programmes, such as the use of entomopathogenic nematodes (EPNs) for the control of codling moth. Entomopathogenic nematodes belonging to either Steinernematidae or Heterorhabditidae are ideal candidates for incorporation into the integrated pest management programme currently being developed for pome fruit orchards throughout South Africa with the ultimate aim of producing residuefree fruit. However, these lethal pathogens of insects are not exempted from governmental registration requirements and have therefore not yet been commercialized in South Africa. A nontarget survey was conducted to find suitable isolates of EPNs from local soils and to test their effectiveness as control agents against the codling moth. Soil samples were collected from several habitats and regions throughout South Africa and nematodes were recovered using the insect baiting technique. All EPN isolates obtained were identified to species level using a molecular taxonomic approach. Entomopathogenic nematodes were recovered from 20 of the 200 soil samples (10 %). Of these, eight (40 %) yielded Steinernema spp., identified as three isolates of S. khoisanae and five undescribed Steinernema spp. The other 12 (60 %) of the samples were positive for Heterorhabditis spp. and included six isolates of H. bacteriophora, five H. zealandica and one H. safricana. These isolates were then evaluated in laboratory bioassays for their potential as microbial agents of codling moth under varying conditions. A morphometric study indicated that all natural openings (mouth, anus and spiracles) of final instar codling moth were large enough for the infective juveniles (IJs) of all tested EPN species to gain entry into the larvae.

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