Wild bees and agroecosystems

Research in agriculture often focuses on development of new technologies rather than on potential environmental impacts. Pollinators, primarily bees, are essential to agriculture, providing significant yield benefit in over 66% of crop species. Currently, dramatic losses of managed honey bee pollinators in North America along with suspected world-wide losses of wild pollinators are focusing research attention on an impending but still poorly documented pollination crisis. Essential questions include: How important are wild bees to crop production? Are current agricultural practices harming pollinator populations? Can agricultural methods be modified in ways that promote pollinators and food production? In this thesis I examine the interaction between modern agriculture and wild bees through 1) laboratory experiments on effects of new genetically modified (GM), systemic, and bio-pest control products on bumble bee (Bombus spp.) health and foraging ability, and 2) field experiments on the impacts of agricultural landscapes on wild bee abundance, diversity, and pollination efficacy. I developed a new method of assessing bee foraging after exposure to pesticides that is a useful and sensitive test for sub-lethal impacts on pollinators. The GM pesticidal proteins Bt Cry1 Ac and chitinase did not negatively affect bumble bee colony or individual health or foraging ability. However, the pesticide imidacloprid in the new chloronicotinoid family of pesticides impaired bee foraging when bees were exposed to elevated doses during larval development. The new biopesticide spinosad, which is widely marketed and approved as an organic insecticide, rapidly killed bumble bee colonies at elevated doses and impaired foraging ability at realistic exposure rates. In field studies, herbicide-tolerant genetically modified canola agroecosystems had fewer wild bees than organic fields, and there were an intermediate number of bees in conventional fields. Low bee abundance in GM fields and to a lesser extent, conventional fields was associated with low seed set and reduced yields. Weed cover in fields and amount of uncultivated land around fields were positively related to bee abundance in fields. We determined that crop landscapes with uncultivated areas could have greater yield than homogenously tilled landscapes. These data can be used to design agroecosystems that benefit both conservation and crop production.