ABAMECTIN RESISTANCE POTENTIAL IN THE GERMAN-COCKROACH (DICTYOPTERA, BLATTELLIDAE)

Twelve field-collected populations of German cockroaches, Blattella ge rmanica (L.), were examined for resistance to dietary abamectin at 40 ppm. Half of these populations had significantly increased resistance ratios compared with the VPI-susceptible strain, but the highest value was only 2.4. Feeding inhibition was variable but nevertheless pronou nced in all 12 strains. Feeding-choice tests with two strains revealed that each strain consumed treated and untreated food about equally. M ortality was reduced in both strains. Cross-resistance from cyclodiene resistance was not found. Low-level selections with abamectin did not result in increased resistance. Whereas resistance to abamectin does not appear to be a problem at present, two potential resistance mechan isms were identified and are discussed briefly.