Colony impacts and adaptive responses to temporal change in nutritional income and pesticide exposure in bumblebees

Abstract

Over the past few decades, the issue of insect pollinator declines, particularly that of bees, has come to the fore. This is concerning given that this important functional group provides a crucial pollination service for many wild and crop plant species. Agricultural intensification has been implicated in causing these declines, but what specific factors are driving them and the mechanisms at play remain unclear. One explanation is that agricultural landscapes change the temporal availability of food resources, which could affect key developmental stages of insect pollinators. Furthermore, the risk of pesticide exposure to insect pollinators foraging or living in such agricultural landscapes may further compound the effect on these potentially susceptible windows in development. Through empirical lab experiments on a key wild pollinator – bumblebees – this PhD looks to understand how temporal variation in food income alongside neonicotinoid exposure affect colony growth and fitness proxies. Overall, food income had the overriding impact on bumblebee colony development and production of sexuals, with pesticide exposure showing little effect in this study. Restrictions in food income earlier in colony development seemed to affect not only worker mass, but also the reproductive performance of the colony by affecting male mass and therefore identifying a potentially vulnerable stage. Food restrictions relatively later in colony development showed a larger effect on the number of males produced, rather than male mass. Further experimentation showed that colonies first attempt to buffer nutritional stress by delaying the development rate of offspring to maintain numbers, but at the cost of producing them smaller. The findings of this study suggest floral availability early in the development of colonies is critical to the rearing of sexuals later in the colony, but that managing landscapes to support early flower phenology cannot come at a cost of lower availability later in the season.