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Botswana International University of Science & Technology (BIUST) 2017

Impacts of climate variability on stemborers-natural enemies trophic level interaction : implications for biological control under global change

Mutamiswa, Reyard

Titre : Impacts of climate variability on stemborers-natural enemies trophic level interaction : implications for biological control under global change

Auteur : Mutamiswa, Reyard

Université de soutenance : Botswana International University of Science & Technology (BIUST)

Grade Doctor of Philosophy-Biological Sciences, Applied Entomology 2017

Résumé partiel
Lepidopteran stemborers are key destructive insect pests of cereal crops in sub-Saharan Africa with the indigenous noctuids Busseola fusca (Fuller) and Sesamia calamistis Hampson and the exotic crambid Chilo partellus Swinhoe accounting for 5-75% of potential cereal crop yield losses. The main larval endoparasitoids comprising, indigenous Cotesia sesamiae and exotic Cotesia flavipes Cameron contribute to a significant extent in managing these economic herbivorous insect pests. However, efficacy of biological control under global change is currently under threat, and factors limiting trophic level abundance, distribution and population phenologies of these insect species under climate change remain unclear. Against this background, this study provides an understanding of the thermal ecophysiology of laboratory reared B. fusca, S. calamistis and C. partellus and their larval parasitoids, C. sesamiae and C. flavipes under variable climatic conditions and how their population phenologies are likely to be shaped by variable thermal regimes under global change scenarios. This study reports implications of these results thereof for biological control efficacy under climate change. Firstly, a comparative assessment of C. partellus and C. sesamiae thermal tolerance using dynamic and static protocols showed developmental stage differences in C. partellus thermal tolerance (with respect to lethal temperatures and critical thermal limits) and a compromised temperature tolerance of C. sesamiae relative to its host. This indicates potential asynchrony between host-parasitoid population phenology and consequently biocontrol efficacy under global change. Secondly, I investigated the short to medium term phenotypic plasticity of thermal tolerance of C. partellus developmental stages (larvae, pupae and adults) and its larval parasitoid C. flavipes (adults). Rapid cold hardening (RCH) and rapid heat hardening (RHH) effects in C. partellus larvae, pupae and adults and C. flavipes adults were highly significant (P ˂ 0.001). In addition, high temperature acclimation (33°C) improved critical thermal limits [CTLs (CTmin and CTmax)] and heat knock-down time (HKDT) for C. partellus larvae and C. flavipes adults (P ˂ 0.0001) respectively while low temperature (23°C) acclimation enhanced supercooling point (SCP) for C. flavipes and chill-coma recovery time (CCRT) for both C. partellus larvae and C. flavipes adults (P ˂ 0.0001) suggesting that the host is more plastic than the parasitoid.

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