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Comparison of pheromone trap bioassays for monitoring insecticide resistance of Phyllonorycter elmaella (Lepidoptera: Gracillariidae)

Shearer, P.W., Riedl, H.
Journal of economic entomology 1994 v.87 no.6 pp. 1450-1454
Phyllonorycter, insecticide resistance, insecticides, topical application, bait traps, pheromone traps, monitoring, mortality, biological resistance, Oregon, Washington
Two pheromone trap assays were evaluated for monitoring insecticide resistance of Phyllonorycter elmaella (Doganlar & Mutuura). For both assays, male moths were collected in the field with pheromone-baited sticky traps. In the first test, we used topical application of 0.2 microliters of an insecticide-solvent mixture to the dorsal surface of each moth. In the second assay, we incorporated the pesticide into the adhesive so that moths were exposed upon capture. The assays were compared for their ability to characterize the response to insecticides of susceptible and resistant field populations of P. elmaella. Both assays adequately described the concentration-mortality response to azinphosmethyl and oxamyl of susceptible male P. elmaella moths. However, only the topical assay was a suitable method for quantifying the mortality response of moths with high azinphosmethyl resistance. Concentration-mortality response lines could not be produced with the insecticide-laced adhesive assay for azinphosmethyl-resistant moths. Moths from commercial apple and cherry orchards treated topically with azinphosmethyl were 56-71-fold more resistant than moths collected from an isolated abandoned site. Azinphosmethyl-resistant P. elmaella male moths were still susceptible to oxamyl. Male P. elmaella moths did not avoid traps with oxamyl-laced adhesive, but moths from azinphosmethyl-resistant populations were repelled by azinphosmethyl at a rate of 10 mg (AI)/g adhesive, indicating the possibility of behavioral resistance and a bias in the collection of test subjects with this bioassay method. Despite these shortcomings, the insecticide-laced adhesive assay may still be useful for diagnostic-dose surveys and for resistance detection programs.