Bio21 - Theses
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ItemParasitism by Trichogramma wasp: potential and reality under climate change scenario, with focus species attacking Asian corn borer( 2016)Climate change may directly influence the distribution of parasitoids, lead to phenological asynchrony with their hosts, and/or lead to other disruptions of multitrophic interactions. By determining the impacts of global warming effects which may influence Trichogramma populations, researchers and land users can be provided with ways to further enhance the efficiency of biocontrol. First, I identified common Trichogramma species emerging from Asian corn borer Ostrinia furnacalis egg masses (based on morphology and internal transcribed spacer 2- ITS-2) throughout southwestern Taiwan. I then compared their life history characteristics and thermal limits and determined the Wolbachia infection status of field-collected parasitoids. Although T. ostriniae and T. sp. y appear to be morphologically similar, the ITS-2 identity between these two taxa is only 89%. A commercially released Trichogramma colony thought to be T. chilonis possessed 99% identity with the field T. sp. y individuals. The current study provides a baseline for future work, and also highlights the importance of accurately identifying species when establishing colonies of natural enemies for biocontrol. Next, I evaluated the distributions of Trichogramma ostriniae and its native host, Ostrinia furnacalis (in southeastern Asia), and target host, Ostrinia nubilalis (in North America), using a combination of MAXENT and CLIMEX modelling approaches. Trichogramma ostriniae was predicted to occur in the summer corn region of China, with distribution limits linked to its sensitivity to cold, and the seasonality of radiation and precipitation. The stepwise modelling approach used here proved useful for assessing environmental factors linked to an egg parasitoid and its lepidopteran host and for identifying areas potentially suitable for inundative releases. Finally, integrating meta-analysis results and reviewing related literature, indicated that both top-down and bottom-up factors could moderate the effect size of egg parasitoids over a range of Extreme High Temperature (EHT) values. These patterns suggest a complex response to climate change, mediated by temperature factors, precipitation seasonality, crop type and perhaps other factors related to latitude. Trichogramma biocontrol efficiency is hampered by extreme climate change as they are more senstive to environmental factors than their hosts. The work presented here highlights effects of precipitation and radiation seasonality on parasitism, life history traits, and distributions of Trichogramma species, which could act to either improve or optimise the execution of lepidopteran biocontrol projects. Results of this study will be useful to managers for successful use of Trichogramma in biocontrol under a climate change future.