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 alfalfa pollinator in the Pacific Northwest. People managing alfalfa leafcutting bees in Idaho, Utah and Colorado reported unusually low numbers of bees being produced in fields that had been treated with novaluron, an insecticide used to control Lygus bugs. Novaluron is an insect growth regulator. We evaluated novaluron toxicity to immature leafcutting bees using two exposure methods: by directly applying pesticides to eggs and bee larvae (and their food provision), or by feeding the insecticide to adult females before releasing them in field cages with blooming alfalfa where nesting and immature mortality were observed. When immature bees were treated, mortality was significantly higher than in both the water-treated and untreated controls, providing evidence that novaluron is toxic to bee offspring in nest cells. The eggs and young larvae were more susceptable than older larvae. When adult female bees were fed the insecticide, nesting was similar to the controls; however, offspring mortality was greater in those treatments where females were fed sugar-water + novaluron compared to sugar-water only. Although novaluron-fed females provided adequate provisions for their offspring, there was a low percentage of egg hatch or larval development. Novaluron could be contributing to poor bee return in alfalfa grown for seed. This agreement was also used to provide chemical analayses of pesticide levels in bee nests from agricultural fields, for honey bees, alfalfa leafcutting bees, and blue orchard bees. Analysis of the results is underway.