Induction of a malathion-resistant strain in the common predacious mite Amblyseius cydnodactylon (Acari : Phytoseiidae)

This study demonstrates a laboratory induction of a malathion - resistant s train in Amblyseius cydnodactylon She-hata & Zaher and effect of selection on reproduction. Initially 500 sensitive females obtained from a laboratory mass culture were exposed to malathion at LC70. Subsequent selections were conducted every two generations at progressive LC70 values and number of e ggs/female/day was recorded at each selection. Experiments were carried out under laboratory conditions of 24-28 degrees C and 70-80 % R. H. The LC70 in the parent generation was 5.19 ppm and increased to 20 ppm in F4 selecti on generation. The dosage mortality relationships continued to increase up to a maximum of 282.3 ppm in F16. The rate of developing resistance increas ed from 1.75 folds in FZ to 1.97 folds in F4 and gradually reached a maximu m of 54.39 folds in F16. There was an obvious decrease in reproduction corr esponded to increasing resistance. For example, the number of eggs/female/d ay in F16 was 8 eggs, contrasting 3 eggs in the parent generation.