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What is the context of this research?

The alfalfa leafcutter bee (ALB) is a solitary bee that builds complex nests for their offspring. Each nest consists of sequential cells made from leaf clippings, and provisioned with pollen and nectar, where a single egg is deposited. Given the central importance of nesting behaviors for bee reproductive success, understanding how environmental stressors change nest building is critical for managing this pollinator. One potential stressor is pesticides used in alfalfa, which adult ALBs encounter while foraging for pollen and nectar. Sublethal doses of these pesticides can disrupt bee behaviors but their effects on nest building such as the number of cells per nest, the size of the nest cap, or offspring sex ratio remain unknown.

What is the significance of this project?

The alfalfa leafcutter bee (ALB) is the second most valuable pollinator in the world after the honey bee. Our preliminary results show that ALB nest building behaviors vary considerably among females and affect offspring body size, sex ratio, and protection from parasites and pathogens. Stressors that impair nest building, such as pesticides, could thus influence bee abundance and health, and in turn affect crop pollination. Many studies have focused on the lethal effects of pesticides, or sublethal effects on bee navigation and foraging, but effects on nest building behaviors are unknown. Further, understanding how nest architecture varies among females and affects bee fitness contributes to our understanding of this pollinator's natural history.

What are the goals of the project?

Our goal for this project is to test whether exposure to neonicotinoid insecticides alters nest building in alfalfa leafcutter bees (ALBs). We will set 9 screened enclosures in an alfalfa field and expose ALBs to 3 different treatments: no insecticide exposure, exposure to a low (sublethal) insecticide dose, and exposure to a high (lethal) insecticide dose. We will compare the following nest components across insecticide treatments including: nest protection (the number and weight of leaves used to build the nest cap), nest size (the length and number of cells per nest) and investment per cell (mass of the food provision per cell, number of leaves per cell, and offspring size and sex per cell).