LRES MS Thesis Defense
- Thursday, July 6, 2017 at 9:00am
- Animal Biosciences Building, Room 138 - view map
Toxicity, exposure, and risk of insecticides used for mosquito management on the alfalfa leafcutting bee, Megachile rotundata
Abstract: The alfalfa leafcutting bee, Megachile rotundata F. (Hymenoptera: Megachilidae), is one of the most managed solitary bees and is an important pollinator of many crops, especially alfalfa, Medicago sativa L. However, little is known about its response to insecticides, specifically pyrethroids, which are frequently used to manage populations of adult mosquitoes. Current regulatory requirements for insecticide toxicity to non-target insects focus on one eusocial pollinator, the honey bee, Apis mellifera L., but this species does not represent all insect pollinator species in terms of response to insecticides. Therefore, we characterized the toxicity and risk of three pyrethroid insecticides (permethrin, deltamethrin, and etofenprox) on adult M. rotundata in both laboratory and field settings. The median lethal dose, LD50, was estimated for adult M. rotundata females when exposed to each pyrethroid to serve as a baseline toxicity test to determine the susceptibility of M. rotundata to these insecticides. The range of concentrations for permethrin and etofenprox ranged from 0.0075-0.076 µg/bee and the range for deltamethrin was 0.0014-0.0075 µg/bee. The estimated LD50 results for permethrin, etofenprox, and deltamethrin was 0.057, 0.051, and 0.0016 µg/bee, respectively. After obtaining the LD50 results, we compared female respiration rates after dosing of each LD50 endpoint. In a field study, we applied a formulated version of each active ingredient at the maximum labeled rate of 0.017 kg/ha over an alfalfa field via ultra-low-volume (ULV) applicator and observed mortality of both adult A. mellifera and M. rotundata for 48-hr after exposure. In both species, there was no significant difference in mortality between control and treated groups for any of the formulations. In another field study, a formulated version of etofenprox was applied in an alfalfa field at the half-maximum labeled rate of 0.003 kg/ha and directly targeted M. rotundata nests. There was no significant difference in mortality between control and treated groups. We also did not observe a significant difference in the number of emerged adults reared between treated vs. control shelters. Results from the field studies suggest that the risk of mortality from these insecticides applied via ULV applicators may be relatively low.
- Department of Land Resources and Environmental Sciences