Location: Pollinating Insect-Biology, Management, Systematics Research
Project Number: 2080-21000-019-100-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Dec 11, 2023
End Date: Jun 30, 2026
Objective:
Determine the safety for alfalfa leafcutting bees of insecticides useful for Lygus bug control.
Approach:
Cage studies will be used to determine if exposure to the insecticides sulfoxaflor (Transform) and afidopyropen (Sefina) result in sublethal effects on alfalfa leafcutting bees, such as reduced foraging effort or reproductive output. Fourteen screened field cages (6.2 x 6.2 x 2 m3) will be erected over a planting of alfalfa located at the USDA ARS Pollinating Insects Research Unit (PIRU) in Logan, Utah. A polystyrene bee board (49 holes) with paper inserts will then be secured to a metal pole 1.5 m above the ground at the center of each cage. Overwintered prepupae of leafcutting bees will be purchased from Jim Watts and incubated at the PIRU at 29°C in June to complete bee development to adulthood to coincide with bloom. We will then release 40 males and 20 females into each cage. Females will be individually marked with paint prior to release in the cage to allow for identification of individuals.
After nesting activity is underway in the cages, we will begin daily behavioral observations. In Week 1, the natural (pre-treatment) activity of female bees will be observed every day for 5 days for 1 hour each day in each cage between the hours of 9am-3pm. Recorded activities will include foraging time and foraging target (leaf pieces versus pollen). We will also record the number of attempts to enter the incorrect nest. In Week 2, we will apply insecticide treatments at the maximum registered application rates for control of Lygus bugs. Water will be applied in the control cages at equal volumes to treatment sprays to serve as a control. Applications will be made in the evening after leafcutting bee activity has ceased. We will then do the same behavioral recordings for the 5 days post application as were done in Week 1. A second application will be made at the start of Week 3 (7-day minimum retreatment interval for each pesticide), and behavior will again be recorded for 5 days. To monitor nesting progress, nests will be x-rayed weekly between dusk and dawn, and the number of completed nests will be recorded. After the completion of the field trial, we will track the development of brood. Nests will be incubated at optimal temperatures, put into cold storage over the winter, and then incubated in the spring to initiate pupation and adult emergence. Developmental timing of brood will be monitored by x-rays until the prepupal stage to evaluate the impact of pesticide exposure on brood development. Emergence of adult bees in the following summer will be recorded.
Additionally, alfalfa clippings will be taken each day of the behavioral observations in Weeks 2 and 3 for analysis of residues, allowing us to determine field exposure levels following applications, and correlate these with any behavioral impacts. A subset of provisioned nests will be excised, and provisions will be analyzed for residues to determine brood exposure through nest provisions. Samples will be analyzed by Dr. Hageman at USU, where they will conduct extractions and residue analysis for the active ingredients in Sefina and Transform using gas chromatography and mass spectrometry (LC-MS/MS).
