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.
Argall J., Mackenzie K., Javorek S., Chiasson G. (1996) Alfalfa leafcutter bees for the pollination of wild blueberries. Department of Agriculture, Aquaculture and Fisheries, Fredericton. New Brunswick, Canada. Available at: http:// www.gnb.ca/0171/10/0171100027-e.asp
EC (2007) Guidance document on statistical methods for environmental toxicity tests. Report EPS 1/RM/46, with June 2007 amendments. Environmental Protection Series. Environmental Science and Method Development and Applications Section Technology Centre. Environment Canada. Ottawa, Ontario, Canada. 283 pp.
EPA (2000) Dichlorvos (62-73-7) hazard summary. Technology Transfer Network - Air Toxics Web Site. United States Environmental Protection Agency. Available at: http://www.epa.gov/ttnatw01/hlthef/dichlorv.html
Goerzen D. W. (2010) Parasite control in alfalfa leafcutting bee populations. Sask Leafcutters Association. 3pp. Available at: http://www.saspa.com/PDF/Parasite%20control%20in%20alfalfa%20leafcutting%20bee%20populations.pdf
Grissell E. E., Schauff M. E. (1997) A handbook of the families of nearctic Chalcidoidea (Hymenoptera), 2nd Edition. Entomological Society of Washington. Washington D.C. 87 pp.
Hayes W. J. (1982) Pesticides Studied in Man. Williams and Wilkins. Baltimore, Md., USA. 672 pp.
Hill B. B., Richards K. W., Schaalje G. B. (1984) Use of dichlorvos resin strips to reduce parasitism of alfalfa leafcutter bee (Hymenoptera, Megachilidae) cocoons during incubation. Journal of Economic Entomology 77: 1307-1312.
Hubert J. J. (1984) Bioassay, 2nd edition. Kendall Hunt Publishing Company. Dubuque, Iowa, USA. 413pp.
R Development Core Team (2010) R: A language and environment for statistical computing. R Foundation for Statistical Computing. Vienna, Austria.
Whitfield G. H., Richards K. W. (1987) The post diapause development and adult emergence of Pteromalus venustus Walker (Hymenoptera: Pteromalidae) during alfalfa leafcutter bee incubation. Canadian Entomologist 119: 491-493.
Wu J. Y., Smart M. D. (2012) Alfalfa leafcutter bee Megachile rotundata pests. In: Hollingsworth C. S. (Ed.) Pacific northwest insect management handbook.. Oregon State University. Corvallis, OR, USA. Available at: http://insects.ippc.orst.edu/pnw/insects?09BEES02.dat