Browsing by Author "Dlamini, Bonginkhosi"

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    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.