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

The efficiency of monitoring for cyclodiene resistance in Drosophila p opulations via insecticide bioassay was compared directly with results from PCR-based genotyping of individual insects (PCR/REN). Insecticid e bioassays were performed on several hundred insects collected from e ach of 10 sites and PCR/REN on only 100 insects per site. The mean res istance frequency estimate by bioassay (0.02) was twice as high as tha t observed by PCR/REN (0.01) and was associated with a greater varianc e. We were also able to document a high frequency of expected RS survi vors in the bioassay that were later genotyped as susceptible (SS). If similar trends hold at higher frequencies of resistance, this could l ead to serious overestimation of resistance frequencies. This study hi ghlights two advantages of PCR/REN over insecticide bioassay (i). Esti mations of resistance frequency via PCR/REN are more precise that thos e derived by bioassay, and (ii) resistance frequencies can be determin ed by PCR/REN with correspondingly smaller sample sizes. The implicati ons of these results for resistance monitoring and for the persistence of resistance genes in untreated populations are discussed. (C) 1994 Academic Press, Inc.