Resistance of Mites Attacking Citrus

Resistance of citrus red mite, Panonychus citri (McG.), to ovex was measurable by laboratory techniques by the eighth filed application. Field experiments were established in 1954 to ascertain the effects of successive and alternating acaricide programs on the number of applications before mites developed resistance to some of the newer acaricides and to measure any decrease in the degree of ovex resistance. Results indicate that a wide variation exists in the rate mites develop resistance to each of the various acaricides. With some acaricides, resistance existed in only one stage of mite development, or at least the susceptibility of the several stages was markedly different. Cross resistance of related acaricides exists, but for citrus red mite it is more general with the organophosphorus compounds than with the chlorinated hydrocarbons. Demeton appeared to be particularly operative in developing mite resistance to related phosphates. The rate resistance developed in alternating acaricide schedules varied with the combinations selected. Where organophosphorus or chlorinated hydrocarbonated acaricides other than ovex were used for 5 years to control ovex-resistant mites, the degree of resistance to ovex had not measurably decreased.