1a. Objectives (from AD-416)
To evaluate the the toxicity of a new pesticide, Rimon, on the alfalfa leafcutting bee. Rimon is a growth regulator inhibitor and is suspected by some beekeepers to be affecting the growth of bee larvae. The pesticide is used in alfalfa seed fields to control lygus bugs. The two main goals of this project are to assess egg mortality when adult bees are treated with Rimon, and evaluate the mortality dose response of eggs and larvae when pollen provisions are treated.
1b. Approach (from AD-416)
Rimon® is a chitin inhibitor insecticide used for the suppression of lygus bug, the most damaging insect in Utah alfalfa seed fields. The active ingredient in Rimon interferes with insect pest development and successful molting, but is supposed to be safe on beneficial and pollinating insects. In the fall of 2007, several Idaho alfalfa seed growers noticed a greater percentage of leafcutting bee cells containing pollen/nectar provisions with no live bee brood from fields that were treated with Rimon. Growers questioned if Rimon could be lethal or sublethal to leafcutting bee eggs or larvae. The potential negative health effects of Rimon on leafcutting bees are valid concerns for growers who will have to purchase more new bees each growing season. This project will provide basic information on the lethal or sublethal effects of Rimon on adult and immature alfalfa leafcutting bees used to pollinate alfalfa using controlled exposures in the laboratory. ARS will provide a supply of bees and expertise in bee biology and how to handle the bees for development and mortality studies. The University will conduct the experiments, analyze the data, and write up the reports.
3. Progress Report
Alfalfa leafcutting bees are the most common pollinators of alfalfa seed in the western U.S. Beekeepers in Idaho, Utah and Colorado reported that bees from fields treated with novaluron (to control lygus) reproduced poorly. The toxicity of novaluron to immature alfalfa leafcutting bees was tested using two different possible mechanisms of exposure. Immature mortality was assessed when nectar and pollen in the nest (the food of immature bees) were contaminated, and when the adults were exposed to novaluron. Mortality of the immature bees was significantly higher in all the novaluron treatments than in the water or blank controls, providing evidence that novaluron is toxic to progeny in bee nest cells. More eggs and young larvae died, as compared to older larvae. Novaluron did not affect female nesting in field cages; however, there was greater immature mortality in cages where females were fed sugar-water that was contaminated with novaluron as compared to sugar-water only. Although adult female bees provided adequate pollen and nectar provisions to their offspring, a low percentage of the eggs hatched and larval development was poorer when females ingested novaluron before mating and nesting. When the plants in the cages were sprayed to treat the adults, Novaluron was also present in the pollen and nectar provisions from the nests. At least 84 percent of progeny died when the mother bees were allowed to mate and nest 24 hours after a novaluron application. Novaluron could be contributing to poor bee production in alfalfa grown for seed. Timely insecticide applications to suppress lygus is an important consideration to improve ongoing bee health. ADODR monitoring is done by site visits and meetings, phone calls, and email.