School of Molecular & Cell Biology (ETDs)

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    Comparison of different bioassay methods for the assessment of dose-response relationships of entomopathogens and toxins against Helicoverpa armigera (Hübner, 1809) (Lepidoptera: Noctuidae)
    (University of the Witwatersrand, Johannesburg, 2024-11) Mogadingoane, Keitumetse Neo; Bouwer, Gustav
    Bioassays are an important tool for developing bioinsecticides against agricultural pests. The aim of this study was to compare two bioassay methods – diet overlay and droplet feeding – to identify the most suitable method for assessing dose-response relationships of entomopathogens and toxins against second instar larvae of Helicoverpa armigera. The toxins used were purified Bacillus thuringiensis Cry1A.105 and Cry2Ab2.820 proteins, the spore-crystal complex (SCC) of B. thuringiensis subspecies kurstaki strain HD-73, and the entomopathogen Helicoverpa armigera nucleopolyhedrovirus (HearNPV). Based on the heterogeneity factor, coefficient of variance (CV) and relative precision, the diet overlay bioassay was determined to be the best fit for use with HD-73 SCC and HearNPV. Suitable bioassay methods could not be determined for the purified B. thuringiensis proteins due to a poor probit model fit and low precision of estimated LC50s and LD50s. Validation of CV and relative precision across bioassays will ensure the most suitable methods are used for sustainable integrated pest management.
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    Diversity and Abundance of Arthropods on Conventional Sugarcane under Field Conditions in South Africa
    (University of the Witwatersrand, Johannesburg, 2024-09) Smith, Roshay; Malinga, Lawrence; Bouwer, Gustav
    Insect diversity and abundance are often the base for formulating strategies that involve the appropriate application of pest control methods, considering the ecosystem services provided by insects. Therefore, the aim of this study was to provide recent baseline data on the diversity and abundance of insects in conventional sugarcane based on two sugarcane fields in KwaZulu-Natal. Three sampling methods, namely pitfall, sticky and water pan traps, were used to sample insects in rain-fed and irrigated sugarcane in Gingindlovu and Pongola from March to October 2022. This study collected 12 493 insects belonging to 14 insect orders and 88 families in rain-fed sugarcane and 22 309 insects belonging to 14 orders and 94 families in irrigated sugarcane. Significant differences in the diversity indices were found between the sampling methods and the sampling periods. This study provides recent baseline data on the diversity and abundance of insects in sugarcane.