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United States Department of Agriculture

Agricultural Research Service

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Research Project: Lethal and Sublethal Effects of a Systemic Pesticide on Alfalfa Leafcutter Bees

Location: Pollinating Insect-biology, Management, Systematics Research

Project Number: 2080-21000-015-24-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 1, 2014
End Date: May 30, 2018

Alfalfa seed growers must defend their crop plants from pest insects while providing an environment that encourages insect pollination of their plants. Recent trends in plant pest control have led to the widespread deployment of systemic pesticides that may contaminate pollen and nectar at the same time they protect other plant tissues. Although residual toxins in pollen and nectar are typically below lethal concentrations, the effects of sublethal concentrations are poorly known. This study focuses on sulfoxaflor (trade name Transform WG, Dow Agroscience), which is under consideration for use in alfalfa fields, and this study seeks to determine its effects on the alfalfa leafcutter bee (ALB). This highly integrated study will examine the effects of pesticide treatment on both the pest and pollinator at different treatment levels, and examines sublethal effects on pollinators. The goals are to determine: the concentration of sulfoxaflor in alfalfa plants that control pea aphid populations, the longevity of adult alfalfa leafcutter bees foraging on sulfoxaflor-treated plants, the sulfoxaflor concentration that reaches bee provisions when adults forage on treated plants, and the survival, brain development, body size and other physiological performance measures of bees that arise from two generations of foraging on treated plants.

Bee performance when foraging on plants treated against pests will be examined in pseudo-field conditions. Alfalfa will be sown at Blandy Experimental Farm in August 2014 for use in summer 2015. Experiments will be carried out either on individually caged plants (aphid experiment) or groups of plants within 3m x 2m x 2m mesh cages (bee experiment). Transform WG will be applied just prior to flowering. Eight treatments (0, 0.75, 1.25, 1.75, 2.25, 2.75, 3.5 and 4.5 oz/acre) will be used and applied with a backpack sprayer. Expt. 1. Sulfoxaflor control of aphids: 64 plants will be individually caged using tomato cages and mesh bags; 4 plants will be assigned per treatment. Plants also will be randomly assigned to 1 of 2 aphid introduction times: the day prior to pesticide application or 1-week after application. Ten aphids will be placed per plant and counted on plants after 1 week. Two leaf collections (5 leaflets per plant) will be made from each plant 3 days after aphid introduction to characterize pesticide levels. Expt. 2. Sulfoxaflor effects on bees: Just prior to flowering, 32 field cages (4 replicates of the 8 treatments) will be placed in the alfalfa (~70 plants/cage). At flowering, 5 females and 5 males will be placed in cages to nest and forage for 14 days. Adult survival and nest completion will be monitored daily. Data taken also will include adult female and larval survival, body size, and overall reproduction per female/cage/day. Flowers per cage will be estimated weekly. Two leaf collections (5 leaflets from each of 5 plants) will be made from each experimental cage for sulfoxaflor analysis. Four uneaten provisions per cage will be taken at the end of each week and analyzed for sulfoxaflor. An additional 10 (total) provisions from the label rate treatment (2.25 oz/acre) will be separated into liquid and solid portions of the provision for separate sulfoxaflor analysis. A bee response curve by dose will be created from these data. A subset of 4 treatment levels (control, the greatest concentration that yields live adults, and 2 equally spaced treatment levels between those extremes) will be used to examine first and second generation effects on physiological responses. Confocal microscopy will be used to measure brain neuropil volume and also cell bodies and locations of amine arborizations of serotonin, octopamine and dopamine in the bee brain (known neurotransmitters, neuromodulators and neurohormones that effect learning and memory). Previous studies of bee brain development have shown that reduced mushroom body development often occurs under physiological stress that is sublethal but nevertheless severely impairs reproduction. Ovaries will be measured, fat body volume quantified by ether extraction of lipids, and hemolymph vitellogenin titer determined through SDS-PAGE gel electrophoresis. Eight adult females from each of these 4 treatment levels will be examined (first generation) while 8 additional females per treatment will be placed in foraging cages for second generation cumulative exposure effects.

Last Modified: 06/24/2017
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