DETECTION OF ORGANOPHOSPHORUS RESISTANCE IN THE SPIDER-MITES TETRANYCHUS-URTICAE KOCH IN PEAR ORCHARDS IN EGYPT

It became essential to develop resistance management to delay the evol ution of resistance. Resistance management requires simple and quick d etection methods by which resistance pests can be detected in field an d in the early stages of resistance development. Because of the sensit ivity to acetylcholinesterase is the most common cause of organophosph orus resistance in spider mites T. urticae, the activity of acetylchol inesterase and its inhibition with paraoxon were measured in spider mi tes susceptible strain S, resistance strain R, and in two field strain s collected from pear trees in Rashid area, Beheira province BR and El -Mamouraa area, Alexandria province AR in Egypt. The resistant strain R was 102-fold resistant to parathion, while the two field strains BR and AR were 59-fold and 11-fold resistant to parathion, respectively. The activity of acetylcholinesterase in R strain and in the two field strains BR and AR are significantly lower than in the S strain, where the percent of activity to that of S strain was 60%, 70% and 81% for R , BR and AR strains, respectively. The reduction in rate of acetylchol inesterase inhibition was 30-times, 29-times and 17-times in R, BR and AR strains for paraoxon, respectively. The broken curves for the two field strains showed heterogeneity in spider mites population, where p ercent of resistant portion was 92% and 55% for BR and AR strains, res pectively. This rapid and simple technique can be directly performed f or the field strains and provides us with reproducible data about the development of resistance to organophosphorus insecticides in the fiel d.