Masters Degrees (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 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.
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.
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.
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.
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.
Entomopathogenic nematodes : characterization of a new species, long–term storage and control of obscure mealybug, Pseudococcus viburni (Hemiptera: Pseudococcidae) under laboratory conditions
(Stellenbosch : University of Stellenbosch, 2009-12) Stokwe, Nomakholwa Faith; Malan, Antoinette P.; Addison, Pia; University of Stellenbosch. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The obscure mealybug, Pseudococcus viburni (Signoret) (Pseudococcidae), is one of the common and serious pests of apples and pears in South Africa. The management of this pest in South Africa is dominated by the use of insecticides, while research into using natural enemies for biological control of mealybugs is still ongoing. Increasing concern over the environmental impact, pesticide residues in fruits, resistance, and expense associated with frequent use of insecticides make it necessary to investigate alternative biological control methods, such as the use of entomopathogenic nematodes, for the control of mealybugs. Entomopathogenic nematodes have proven comparable or even superior to chemicals in controlling certain insect pests, without residue problems or a harmful effect on the environment. An important aspect of using endemic nematodes includes the identification of species of nematodes and their symbiotic bacterial cells. A study was carried out to describe a new species of Steinernema, which was recovered during a previous survey in citrus orchards in three provinces of South Africa. Morphometrics, morphology, crossbreeding, drawings, light microscopy and Scanning Electron Microscopy (SEM) photographs were used to describe the new species. A cryopreservation method has been simplified and optimised for the long-term storage of Steinernema khoisanae (SF87) and Heterorhabditis zealandica (J34). Different cryoprotectants used included 15% glycerol, 8% ethylene glycol and 8% dimethyl sulfoxide (DMSO), in which S. khoisanae was incubated at room temperature for periods of two, three, four and five days, followed by a methanol wash. An optimum survival rate of 69% was obtained for S. khoisanae after a four-day incubation period in 15% glycerol. This technique has been used for the cryopreservation of H. zealandica, with a 78% survival rate. The thawed nematodes of both species were able to infect Galleria mellonella larvae after 42 days of cryopreservation (-196ºC) and were able to complete their life cycles.
Fruit fly (Diptera : Tephritidae) ecology in the Western Cape, South Africa
(2015-12) Geldenhuys, Marinus; Addison, Pia; Manrakhan, Aruna; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) and the Natal fly C. rosa Karsch are two important tephritid pest species of commercially grown deciduous fruit in the Western Cape. Detailed information on the status of these two fruit fly species in terms of the influence that different host fruits have on their development, abundance and distribution in this region is not known. This project investigated the status of the two fruit fly species in the Western Cape by a) determining the influence of different fruit types on life table parameters such as egg development, larval development, pupal success rate, adult emergence, fecundity and adult survival, b) assessing trapping data and fruit infestation from home gardens in or near areas where deciduous fruits are grown commercially, in order to determine relative abundances and distribution of C. capitata and C. rosa in the region, and c) using geometric morphometrics to assess variability in development associated with host type, by determining shape variation in the wings of C. capitata that were reared on different host fruits. Life table parameters of C. capitata and C. rosa were determined with a series of laboratory experiments on “Golden delicious” and “Granny smith” apples (Malus domestica L. Borkh.), “Crimson seedless” and “Dauphine” grapes (Vitis vinifera L.), “Excellence” peaches (Prunus persica Sieb. & Zucc.), “Packham‟s triumph” pears (Pyrus communis L.), “Angeleno” plums (Prunus japonica Thunb.), “Navel” oranges (Citrus sinensis Osbeck), clementine (Citrus unshiu Swingle) and “Fan Retief” guava (Psidium guajava Linn.). To gain a broader understanding of the population dynamics of fruit flies, on different commercial and non-commercial host plants in various fruit growing areas during different months of the year, baited traps were installed and fruit infestation of known and potential host fruits were assessed at selected sites. Geometric morphometrics were used to assess shape variation of wings of a F1 generation of C. capitata reared on different host fruits, namely plum, pear and clementine that were of the same varieties as mentioned above. No significant differences (p = 0.773) were found in egg hatch between fruit fly species on the different deciduous fruit types grown commercially in the Western Cape: grape, plum, pear, apple and peach. No positive puncture response was found on oranges, therefore this fruit type was excluded from further analyses. Ceratitis capitata and C. rosa favoured guavas and displayed significant preferences for this fruit in terms of field collected samples and developmental parameters. Developmental success was significantly higher on guavas compared to other fruit types tested, for males and females (p < 0.015), of both C. capitata and C. rosa. Piquanté peppers (Capsicum baccatum L.) and jambos (Syzygium jambos (L.) Alston) were also significant alternate host plants based on high fruit infestation rates in the field and they should be the focus of control actions in home gardens. Patterns of relative abundance of the two fruit fly species were found to adhere to seasonality in terms of host availability and certain abiotic factors such as annual rainfall and elevation. Ceratitis capitata was found to be the dominant species, as has been recorded previously in other studies. Significant differences were found in the wing shape of males and females of C. capitata only. Shape variation was significant for flies reared on different fruit types, more so for males. These results suggest developmental differences for flies reared on different hosts. Results of the present study can be used to gain a better understanding of factors that determine the relative distribution of these two species and which hosts they more readily infest in the Western Cape. Key words: Fruit flies, host, abundance, distribution, development
The importance of renosterveld conservation based on insect diversity sampled in West Coast Renosterveld in the Western Cape of South Africa
(Stellenbosch : Stellenbosch University, 2016-12) Stander, Arne; Veldtman, Ruan; Addison, Pia; Veldtman, Antoinette; Stellenbosch University. Faculty og Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Research in the Fynbos Biome mainly focussed on the exceptional high plant diversity, especially of the Cape Floristic Region. However, there remains a poor understanding of the insect life found in this region and throughout the Fynbos Biome. The purpose of this thesis was to reduce this knowledge gap, and to add conservation value to the West Coast Renosterveld based on the insect life. This thesis is also the first to document insect diversity at community-level in a highly threatened and fragmented vegetation type in South Africa. West Coast Renosterveld, along with the other renosterveld types, is threatened by agricultural development due to the nutrient richer soils compared to the other vegetation types of the Fynbos Biome. From a conservation point of view, West Coast Renosterveld is in a critical state, with only 3-4% remaining. I used various sampling methods over four seasons to document insect species found in four West Coast Renosterveld patches in the Cape Winelands district, Western Cape. I analyse the effects of sampling methods, seasons and location on the community composition data, and calculate both alpha and beta diversity measures for the four renosterveld patches. The first part of the thesis investigated the effects of sampling method and season on the documented insect species richness and abundance of the insect communities. D-vac, sweep net, pitfall traps, and pan traps were the sampling methods used for this study. Sampling was done over all four seasons in the first year. The combined sampling methods and seasons delivered a total of 851 morphospecies, consisting of 17 orders and 155 families. The sampling methods used in the West Coast Renosterveld did not have an effect on insect species richness or abundance, but did determine how many species and what number were sampled. In addition, seasons are an important driving factor of insect communities in the remaining renosterveld areas. The sampling effort applied in this study thus suggests that renosterveld is rich in insect fauna. Furthermore, a feasible and logistical sampling strategy is proposed which can be used for future insect sampling in renosterveld and other Fynbos Biome vegetation types. The second part of the thesis compared the insect species richness and abundance of four renosterveld areas and investigated what the possible variables are affecting the variation between these areas. J.N Briers-Louw had the highest insect diversity compared to Papegaaiberg, Kooppmanskloof and Spier. Beta diversity was the smallest between any combination with J.N.Briers-Louw and yielded greater diversity when representing the whole region, compared to any other two renosterveld areas. Based on the results, it can be assumed that habitat characteristics have the biggest effect on insect diversity in renosterveld, which is altered by factors including disturbance and topography. Considering these contributing factors, this study found that insect diversity differs greatly between West Coast Renosterveld remnants with only about 20% of the species shared between patches. This emphasises the importance of conserving all remaining renosterveld patches. Also, with this study’s documentation and explanation for the insect diversity found in West Coast Renosterveld, future research can now focus on specific taxa and plant-insect relationships to better understand the ecological functionality of insects in renosterveld.
The in vivo production of Heterorhabditis zealandica and Heterorhabditis bacteriophora
(Stellenbosch : Stellenbosch University, 2012-03) Van Zyl, Carolina; Malan, Antoinette P.; Addison, Pia; Addison, M. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The agricultural industry in South Africa is dominated by the use of insecticides. Producers rely heavily on chemicals that cause increased risk to health, the environment and ecology, rapid resistance development in key insect pests and pesticide residues on crops. The increased concern regarding the impact of these pest management practices on the environment and alternative pest management strategies are being investigated. Entomopathogenic nematodes (EPNs) have been identified as being promising biological control agents of key insect pests. The two EPN genera that have shown promise for use as biological control agents within an integrated pest management programme areSteinernema and Heterorhabditis. Commercialisation and the successful use of EPNs to control pests in North America, Australia, Europe and Asia have confirmed the effectiveness of these organisms as biological control agents. Unfortunately, EPNs in large enough numbers for commercial field applications are not yet available on the South African market. Large numbers of EPNs can be produced through either in vivo or in vitro culturing practices. The objective of this study was to streamline the in vivo production process by using two endemic EPN species, Heterorhabditis zealandica (SF41) and H. bacteriophora (SF351). These EPN isolates have been shown to be effective control agents of codling moth Cydia pomonella, false codling moth Thaumatotibia leucotreta, obscure mealybug Pseudococcus viburni, and the banded fruit weevil Phlyctinus callosus. A comparative study was conducted to identify suitable host insects for EPN production of local H. zealandica (SF41) and H. bacteriophora (SF351) strains. Hosts were selected according to their susceptibility to the two EPN species used, their general availability and the ease and cost of rearing. Wax moth larvae Galleria mellonella (WML) and mealworms Tenebrio molitor (MW) were selected as hosts. In order to produce nematodes of consistent quality, a continuous source of host insects reared on a standardised diet was required. WML and MW were each reared on five different diets in the dark at ±26°C. A superior diet for each host was selected according to the diet that produced, on average, the larvae with the highest body mass within a specific timeframe. The heaviest WML, at an average weight of 0.19 g per larva, were produced on a diet consisting of 118 g wheat flour, 206 g wheat bran, 118 g milk powder, 88 g brewer‟s yeast, 24 g wax powder, 175 ml honey and 175 ml glycerol. The heaviest MW larvae weighed, on average, 0.0154 g per larva, and were produced on a diet consisting of 100% wheat bran. To confirm the hypothesis that a linear relationship exists between the weight of a host and the number of nematodes produced from that host, a study was conducted to determine the number of H. zealandica and H. bacteriophora produced per g of host. WML, MW, codling moth larvae and false codling moth larvae were weighed individually and inoculated with the two nematode species respectively. In addition, nematode production in frozen MW and WML was tested. The number of nematodes harvested from each host was counted, and the average number of nematode progeny produced in each host was calculated. A significant linear correlation between the weight of WML and MW and the number of H. zealandica and H. bacteriophora respectively produced confirmed the hypothesis that nematode production within the specified host increases with an increase in host weight. WML produced the highest number of H. zealandica and H. bacteriophora per g of host (1 459 205 ± 113 670 and 1 898 512 ± 94 355), followed by MW larvae (836 690 ± 121 252 and 414 566 ± 67 017). Lower numbers of H. zealandica and H. bacteriophora per g codling moth (57 582 ± 10 026 and 39 653 ± 8 276) and per g false codling moth (192 867 ± 13 488 and 97 652 ± 23 404) were produced. Successful infection of a suitable insect host is one of the key factors in an efficient in vivo nematode production process. Three inoculation techniques were compared using H. zealandica and H. bacteriophora: inoculation with a pipette; shaking of hosts in the nematode inoculum; and immersion of hosts in the nematode suspension. With each inoculation technique, WML and MW were used as host larvae and were inoculated with nematodes at a concentration of 200 infective juveniles (IJs) / larva. The percentage mortality of insect hosts was determined after two days, and EPN infectivity, confirmed by colour change and dissection, after seven days. The highest percentage EPN infection was obtained using pipetting for both nematode isolates and hosts. Nematode infection rates for all nematode-host combinations obtained with pipetting were above 90%, with the exception of MW inoculation with H. bacteriophora, where the percentage of infection obtained was 76%. The current study conclusively demonstrated that variations in infection levels occur, depending on the inoculation technique used. In an additional effort to enhance infectivity during inoculation, H. zealandica, H. bacteriophora and MW were subjected to host-stressor regimes and to nematode- infectivity-enhancing additives. Three treatments, plus a control treatment, were compared. Exposing MW to 70°C tap water prior to inoculation did not increase infection levels. On the contrary, reduced infection levels were observed with host immersion in 70°C tap water followed by inoculation with H. bacteriophora, compared to the control. Only 12% infection was obtained compared to the 48% infection achieved in the control. Infection obtained using H. zealandica was 21%. Treating H. zealandica and H. bacteriophora IJs withMn2+SO4.H20 in a suspension, prior to inoculating MW, did not significantly enhance nematode virulence. Inoculation of MW with treated H. zealandica IJs led to an infection rate of 81%, compared to the control, with which 80% infection rate was obtained. Heterorhabditis bacteriophora caused 47% MW infection, compared to the control, which was subject to 48% infection. A combination of the two above-mentioned treatments did not enhance the infection levels either. Immersing MW into 70°C tap water prior to inoculation with nematodes treated with Mn2+SO4.H20 led to infection levels of 13% and 9% respectively when H. bacteriophora and H. zealandica were used. Future research is required to optimise the protocol used in this study of subjecting MW and local nematode isolates to stressor regimes. The ability of two formulations to maintain biological activity and virulence of H. zealandica was investigated. A quality standard control measure was used to measure the percentage survival and virulence of formulated H. zealandica over a period of 21 days. IJs were formulated into Pesta granules and coconut fibres, while nematodes stored in tap water served as the control. The numbers of live H. zealandica in Pesta granules and coconut fibres decreased drastically after seven days of storage. The survival of nematodes in Pesta granules dropped to 9.79% after 21 days compared to the control, where the survival rate was 79.79%. Nematode survival in coconut fibres was even lower, at 25.84% after seven days and 2.25% after 21 days. After 21 days in storage, 100%+of nematodes survived in the control for coconut fibres. The application of the standard quality control measure, which was used to determine the virulence of formulated H. zealandica, proved to be ineffective. Higher MW mortality rates were obtained in the control where no nematodes were added to larvae, compared to where nematodes were added in varying dosages. However, adjusting certain aspects in the protocol of this quality control measure specifically to accommodate local conditions could possibly make it a more effective tool for measuring endemic nematode virulence.
Initial investigation of Trichogrammatoidea lutea (Hymenoptera: Trichogrammatidae) as biological control agent of codling moth, Cydia pomonella (Lepidoptera: Tortricidae), in apple and pear orchards, under sterile insect technique (SIT)
(Stellenbosch : Stellenbosch University, 2008-12) Wahner, Nadine; Addison, Pia; Addison, Matthew F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
Codling moth (CM), Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the major pest of apples and pears in the South Western Cape, South Africa. Apart from conventional insecticide sprays, area-wide biologically intensive control methods, such as Sterile Insect Technique (SIT) and pheromone mediated mating disruption (MD) are currently in use on two farms in the Elgin valley. The indigenous parasitoid Trichogrammatoidea lutea Girault (Hymentoptera: Trichogrammatidae) attacks eggs of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), as well as CM and has been found to have considerable parasitism potential on both. Elevated host egg numbers, as achieved by SIT are thought to support establishment of populations of these natural enemies in the orchards. For rapid and secure Trichogrammatoidea species identification, the ITS2 sequences of Trichogrammatoidea lutea and T. cryptophlebiae Nagaraja (an indigenous FCM parasitoid on citrus) were determined and species specific primers were developed. Lifetable studies of T. lutea indicated an optimal temperature for reproduction at around 20 °C. Food was provided by the application of honey-solution soaked cotton wool, behind fine netting. The effect of food provision by this method was found to be dependent on temperature. The acceptance of CM eggs from sterilized vs. fertile parents and of radiation-sterilized eggs vs. fertile ones was assessed in choice trials. While no difference was observed between radiated and fertile eggs, sterile eggs from irradiated parents were significantly less attractive than eggs from fertile parents. In several field studies the dispersal capacity and population sustainability of released T. lutea were investigated. Trials took place in apple and pear orchards in the Elgin valley that formed part of an area-wide sterile CM SIT program. Most of the wasp releases were carried out within blocks of up to 1 ha. A square grid of up to 36 monitoring trees per block allowed spatial distribution analysis. Following single central point releases, parasitism of sentinel eggs was recorded until the end of all experiments, the longest of which lasted 37 weeks. T. lutea females were found to disperse up to 73 m, within one week. Studies concerning toxicity of four commonly used insecticides and one fungicide to immature and adult T. lutea indicated no to low susceptibility of wasps at egg- to first-instar-stage within host eggs. Contact toxicity of the tested materials to adults differed significantly, depending on the compound. All five pesticides caused significantly higher mortality among adults relative to the control. The overall aim of above studies was to determine the potential of T. lutea for broad-scale releases against CM, within a broader integrated pest management program in apple and pear orchards in the Western Cape.
Integrative taxonomy of the endemic Karoo agile grasshoppers, the Euryphyminae
(Stellenbosch : Stellenbosch University, 2018-03) Tshililo, Precious; Bazelet, Corinna S.; Addison, Pia; Karsten, Minette; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The Euryphyminae are a small, African subfamily of grasshoppers which are not very well known. They are endemic to sub-Saharan Africa and consist of 23 genera, 16 of which have records of occurrence in South Africa. They are extremely agile and difficult to either catch or spot. Morphologically they are adapted to arid regions. The aim of this study was to use an integrative taxonomy approach to fill gaps in knowledge relating to Euryphyminae taxonomy and diversity in the Karoo biome. I collected all Euryphyminae information from literature and digitized 626 museum specimens which had been positively identified. I also conducted two month-long sampling trips and collected 624 specimens of Euryphyminae in thirty sites across the southern Karoo biome. Utilizing all data at my disposal, I conducted the first taxonomic review of South African Euryphyminae, investigated morphological and molecular variation within one speciose genus, Euryphymus, and analysed the ecology and diversity of Euryphyminae across space and time in the Karoo. In Chapter 2, I investigate the relationships among Euryphyminae genera by comparing morphological characters and molecular markers from three genes. I find that while most Eurphyminae genera are monophyletic and well-resolved, the evolutionary history does not comply with easily visible morphological traits. I provide an updated key to males of the Euryphyminae genera. In Chapter 3, I first classify various individual of genus Euryphymus on the basis of their morphology. I then use DNA barcoding to determine the relationship between individuals with various polymorphism. Results show that individuals group into five valid species using the 3% species divergence cutoff which is most commonly used for insect phylogenetics. Of these five species, some may be new to science and may require species description. This study shows that variation among and within Eurypyhminae genera is very high and that morphology alone may not be sufficient to differentiate among species. Finally, in Chapter 4, I investigate species richness, abundance and species composition of the Euryphyminae across space and time. I find that there are at least two distinct peaks of Euryphyminae abundance containing different species. Futhermore, most Euryphyminae species seem to be localized to a particular place and time, as most Karoo sites were dominated by one Euryphyminae species at a particular time, but this species composition turned over with the different seasons. This ecology seems to be closely tied to the arid ecosystem which Euryphyminae is specially adapted to utilize. As the first ever in-depth study on Euryphyminae, this study reveals that Euryphyminae are diverse and abundant in the Karoo biome. There may be many more as yet undiscovered species, and many of the known genera require taxonomic revision. Taxonomic revision will benefit from utilization of genetic traits. Furthermore, the evolutionary history of the Euryphyminae is not straight-forward and requires investigation to better understand how and when the Euryphyminae became specially adapted to utilize the arid and sparsely inhabited Karoo biome. Results from this study will be analysed in conjunction with results from ten other plant and animal taxa sampled in the same sites through SANBI’s Karoo BioGaps project. As a whole, these data will be used to aid in government decision making for the management and conservation planning of the Karoo, especially as it relates to shale gas exploration or fracking.

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