1a. Objectives (from AD-416)
We propose to investigate alternative chemistries for control of lygus bugs in alfalfa seed, and predacious beetles in alkali bee beds. Pollination by leafcutting bees, Megachile rotundata, or alkali bees, Nomia melanderi, is essential for seed set in alfalfa seed production. Bee mortality that results from inadvertent exposure to pesticides, disease, parasitism, or direct predation can negatively impact seed yield. In-field pesticide use recommendations are based on the safest timing and bloom conditions for given chemicals, but data on pesticide toxicity to many new chemicals are unknown. In addition, alkali bee nests are subject to predation by ground-dwelling predacious beetles. Azinphos-methyl is the only registered pesticide for control of these predatory beetles, but it only has been granted a 24C registration through 2012, this use will not extend any further due to the fact that the product will no longer be manufactured. Additionally, azinphos-methyl is an extremely toxic insecticide. Thus, alternative controls are needed.
1b. Approach (from AD-416)
We seek to identify compounds that are effective at controlling pests, but that are safe to pollinating bees in alfalfa seed crops. To identify such compounds, we will use three different tests: (1) large-scale, replicated alfalfa seed field tests using 20-acre blocks treated with candidate compounds for lygus control; (2) laboratory bioassays where leafcutting and alkali bees are exposed to treated alfalfa plants; and (3) monitoring of alkali bee beds in Washington state to determine beetle populations. After initial populations are assessed, we will treat the plots with several insecticidal treatments. ARS will provide 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
Bees and blister beetle populations were monitored in alkali bee beds. A hydraulic soil core sampling device that connects to a back hoe and is powered by the hydraulics that would typically be used for a packer plate was constructed and used to sample alkali bee beds. In fall 2009, cores were used to sample from 11 of the 13 active bee beds in the Touchet-Gardena growing district. Additionally, 64 pitfall traps were placed in a seed field near an active bee bed in spring 2009. These pitfall traps were monitored weekly from April 23 through May 21, 2009. Blister beetles were present in April and their population abundance increased through May. Alfalfa seed growers expressed that they were mostly unconcerned with blister beetles, and assumed that pyrethroids applied pre-bloom for lygus bug control reduce their blister beetle populations. Thus, these pesticide trials were not conducted. The effect of three pesticides (chlorantraniprole, indoxacarb, and acetimiprid) used to control other alfalfa seed pests were evaluated for their effect on bees. Pesticides were applied to 0.01 acre plots of alfalfa in Prosser and Touchet, WA, at labeled rates. Residues on the plants were allowed to age for different time periods, then mortalities of alfalfa leafcutting bees and alkali bees were exposed to these residues for 24 hrs with leafcutting bees, and for 8 hrs with alkali bees. Based on the results, caution should be used when applying acetimiprid, which caused 48 percent mortality in leafcutting bees and 32 percent mortality in alkali bees. ADODR monitoring is done via phone calls, e-mails, and discussions at professional meetings.