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
Caged bee release studies were used to evaluate whether Rimon could affect the health of eggs and bee larvae produced by mother bees exposed to the insecticide. Four field cages were placed over alfalfa in bloom at the Utah State University Greenville Farm in Logan, Utah. A small ALCB nesting block was placed in the center of each cage, and 15 female bees were released into each cage on 16 July, 22 July, and 3 August; 18-23 males were released in each cage one day prior to the female releases. Two cages had females feeding on sugar-water for 24 hours prior to release, and the other two cages had females feeding on sugar-water + field-rate Rimon for 24 hours prior to release. For each replication, females foraged and nested within their respective cages for 7-9 days. Each nesting block was replaced between replications. Percent mortality of the progeny was evaluated, and for the first replication, there was 100% progeny mortality for the two cages where ALCB female adults were fed sugar-water + Rimon. These results can be compared to 12 and 20% progeny mortality for the two cages where ALCB females were fed sugar-water but no pesticide. Decreasing flower availability and increasing pest pressure over time in all cages likely reduced optimal nesting during the second and third replications. In all four cages of the first replication, females produced similar number of eggs; although most were not viable in the sugar-water + Rimon treatment. Most of the progeny were dead eggs or young larvae. It appears that when ALCB females feed on Rimon, it affects the health of their progeny. The direct effects of Rimon on alfalfa leafcutting bee larvae and eggs was evaluated in laboratory bioassays. The insecticide was applied directly to eggs in the bee cells with natural provisions. Rimon was tested at 4 rates, and 2 controls were used (a water-treated and an untreated control). The experiment was replicated 4 times over the season. Percent mortality for the four Rimon treatments ranged from 79 – 98%. For all replications, the 4 Rimon treatments were significantly more lethal than the water and blank controls, but mortality in the controls was greater than desired (mean of 56%). Cell handling, chalkbrood, and other environmental factors caused control mortality. ADODR monitoring included on-site visits, phone calls, and e-mail.