ASSESSING AND ENHANCING THE CONTRIBUTIONS OF NATIVE BEES TO AGRICULTURAL POLLINATION

Bee pollination is a critical input to the production of most of the world's food crops. In North America, the managed honey bee (Apis mellifera) provides much of the agricultural pollination with an estimated annual value exceeding $15 billion. Domesticated honey bee stocks continue to suffer high annual mortality, averaging 35-40% over the past 5 years. Such historically-unprecedented loses arise from a combination of challenges, including disease, nutritional stress and environmental toxins (pesticide exposure). These challenges highlight the risk of relying solely on honey bees to provide California's agricultural pollination. Native wild bees also provide important pollination to numerous crops when their habitat and resource needs are met. In some cases their contributions exceed those of managed honey bees, and in others they synergize pollination by honey bees. However, wild bee populations also are threatened by intensification of agriculture and our understanding of how wild bee species and communities respond to habitat quality and environmental toxins remains limited. The overall goals of this project are to quantify threats to bees across working agricultural landscapes, create tools for predicting specific crop-management-landscape combinations that represent particular risks, and develop and promote strategies that mitigate threats.A key driver behind the loss of wild pollinators within intensive agricultural landscapes is likely to be the lack of sufficient floral resources throughout the flight season of the bees. Although certain flowering crops offer resources pulses, there are few flowers to maintain bees between these flowering bonanzas. Restoration of habitat containing diverse native flowering plant communities can help to bolster native pollinators and increase the level of pollination they provide to crops. These same plantings may also enhance honey bee health by providing a more diverse diet and reducing nutritional stress of the colony. In addition to insufficient forage resources, wild bee species also may be limited by insufficient nesting substrates. Finally, recent research indicates solitary and social wild bee species may be especially sensitive to pesticide exposure. Thus two classic ecological concepts have critical practical relevance for addressing threats to bees. The first is understanding the relative importance of multiple limiting resources to animal populations. Bolstering forage for bees where populations are limited by nesting opportunities would have little impact. Although research has begun on wildflower plantings to benefit pollinators, little is known about how these planting can provide nesting resources. The second is bottom up versus top down regulation. Despite high quality resources that promote populations from the bottom up, lethal and sublethal environmental toxins may limit populations from the top down.This project builds on results from previous ones and extends work in new directions. It combines objectives that support the goal of promoting robust populations of wild bees that can be integrated with healthy honey bee populations to provide reliable pollination for California agriculture.Objective 1: Develop spatially explicit maps of pesticide loading for target CA agricultural counties.Objective 2: Quantify key nesting habitat for native bumble bee across working landscapes in Northern CA.Objective 3: Test the ability of habitat plantings designed to support bee forage to also promote nesting habitat for wild bees.Objective 4: Identify native wildflower species and mixes that best support wild bees and honey bees in agricultural contexts and can be used to benefit alternative functions, e.g., pest management for agriculture.Objective 5: Refine strategies for the cultivation of native wildflower (so called pollinator habitat), specifically examine the importance of species diversity and seeding density. These variables may be used to develop reduced-cost wildflower mixes.