Bioassay for Detection of Dichlorvos Insecticide in Air in Alfalfa Leafcutting Bee (Megachile Rotundata F.) Incubators

• Main Authors: Purdy John R., Kevan Peter G.
• Format: Article
• Language: English
• Published: Sciendo 2014-12-01
• Series: Journal of Apicultural Science
• Subjects: bioassay; dichlorvos; lc50; megachile rotundata; pteromalus venustus
• Online Access: https://doi.org/10.2478/jas-2014-0021

Dichlorvos is an insecticide used in slow-release plastic strips for controlling chalcid wasp parasites, such as Pteromalus venustus Walker, in incubators used to raise alfalfa leafcutting bees (Megachile rotundata F.). Beekeepers need a practical method to detect dichlorvos in air and verify that it has dissipated to levels acceptable for worker re-entry and for the bees to emerge. We evaluated three methods for analysis of the dichlorvos concentration in air. Vapor sampling tubes using a manually operated pump or diffusion collection had insufficient sensitivity in the concentration range of interest. Air samples collected using battery powered pumps were analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS), which was accurate and sensitive, but too costly and slow for practical use. Finally, a convenient bioassay for detecting dichlorvos in air was developed using leafcutting bees and verified by comparison with the results obtained by LC/MS/MS for a series of dose levels. The bioassay is simple enough to be done by the beekeeper on-site, is inexpensive, and gives results within 1 h. The LC50 for dichlorvos vapor in air after 1 h of exposure was 273.2 μg/m3 by the probit regression method or 277.3 μg/m3 by the logit regression method.