DIRECT COMPARISON OF PCR-BASED MONITORING FOR CYCLODIENE RESISTANCE IN DROSOPHILA POPULATIONS WITH INSECTICIDE BIOASSAY

The efficiency of monitoring for cyclodiene resistance in Drosophila populations via insecticide bioassay was compared directly with results from PCR-based genotyping of individual insects (PCR/REN). Insecticide bioassays were performed on several hundred insects collected from each of 10 sites and PCR/REN on only 100 insects per site. The mean resistance frequency estimate by bioassay (0.02) was twice as high as that observed by PCR/REN (0.01) and was associated with a greater variance. We were also able to document a high frequency of expected RS survivors in the bioassay that were later genotyped as susceptible (SS). If similar trends hold at higher frequencies of resistance, this could lead to serious overestimation of resistance frequencies. This study highlights two advantages of PCR/REN over insecticide bioassay (i). Estimations of resistance frequency via PCR/REN are more precise that those derived by bioassay, and (ii) resistance frequencies can be determined by PCR/REN with correspondingly smaller sample sizes. The implications of these results for resistance monitoring and for the persistence of resistance genes in untreated populations are discussed. (C) 1994 Academic Press, Inc.