Field Musca domestica populations were tested for methomyl resistance using three different assays. The first assay used a topical application (0.4µl) to measure the contact toxicity (LD50). The second test used a no-choice feeding bioassay (different concentrations of methomyl in sugar) to measure ingested toxicity (LC50). The third assay provided flies with a choice between untreated sugar and commercial bait. This assay measured lethal time (LT50) and also included the opportunity for behavioral resistance to be expressed. Relative to a susceptible UC Riverside colony, field populations displayed resistance ratios ranging from 1.1x to 9.1x using the topical or no-choice feeding assays. However, there was a remarkable increase in resistance (42x to over 200x) in the choice assay, suggesting some type of behavioral resistance. Two supplementary tests were used to evaluate behavioral resistance to these baits: a C14 feeding study to quantify ingestion and a bait attraction assay.
Keywords: Musca domestica
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA