Plastic responses as drivers of fitness in Sitotroga cerealella (olivier)

Abstract

Models predict increase in both global temperatures, means and the magnitude of seasonal and daily temperature variations. These changes are likely to impact insect species physiology and phaenology. However, the ability of insect species to adapt to these shifts in temperature remain a mistery. Nevertheless, it has been documented that insects use a wide variety of mechanisms such as phenotypic plasticity to cope with extreme environmental stressors. This mechanism has been reported to allow the organisms to cope with environmental unpredictability and or heterogeneit. Despite this knowledge, it is unclear how much plasticity in thermal tolerance will impact insect response to global warming, particularly over generations. Insects in the visited local storage facilities are frequently exposed to high temperature stress due to the enclosed nature and relatively small size of grain storage facilities. However, the possibility for this climate induced continuous pre-conditioning to create heat resilient storage pest phenotypes through beneficial acclimation remain unknown and is also likely to worsen under current and projected climate change. This work was therefore aimed at investigating carry over effects of heat and starvation acclimations (chapter 3) and cold and desiccation acclimations (chapter 4) on the thermal tolerance of adult Sitotroga cerealella across generations. I found out that, heat acclimation (acute and dynamic) showed reduced heat tolerance measured as both CTmax and Heat knockdown time on S. cerealella. These results are however not surprising as although insects are able to quickly respond to changing environmental conditions through phenotypic plasticity, phenotypic plastic responses have been reported to be reversible as well as not fixed. I also found that fasting (food deprivation) acclimation did not significantly affect CTmax, indicating a lack of evidence for cross tolerance and/or susceptibility. Similalry to starvation acclimation, both cold and desiccation acclimation showed reduced thermal tolerance, suggesting lack of inter-generational crosstalk in heat stress following both cold and desiccation acclimation in S. cerealella. This work provides knowledge on how phenotypic plasticity is likely to contribute to the survival of S. cerealella under the ongoing global warming. The information is critical in that it can be used in the impropvement of grain treatment methods, thereby contributing towards global food security.