Factors influencing pesticide resistance in Psylla pyricola Foerster and susceptibility in its mirid predator, Deraeocoris brevis Knight

Pear psylla, Psylla pyricola Foerster, from the Rogue River Valley, Oregon, were resistant to several insecticides compared with pear psylla from Corvallis, Oregon, as indicated by topical application bioassays. In both strains of psylla, insecticide toxicity showed seasonal variation, and winter-form psylla were less susceptible than summer-form psylla. The effects of the insecticidal synergists piperonyl butoxide (PbO) and DEF in resistant pear psylla indicated that cytochrome P-450 monooxygenases and esterases were involved in detoxification. P. pyricola from the Rogue River Valley were ca. 37-fold more tolerant to azinphosmethyl and ca. 7-fold more tolerant to fenvalerate than its mirid predator, Deraeocoris brevis Knight.; Factors influencing pesticide susceptibility and resistance in P. pyricola and D. brevis were studied at the biochemical, life history, and population ecology levels.; Studies on detoxification enzymes showed that glutathione S-transferase and cytochrome P-450 monooxygenase activities were ca. 1.6-fold higher in susceptible D. brevis than in susceptible pear psylla, however, esterase activity was ca.. 5-fold lower. Esterase activity was ca. 18-fold higher in resistant pear psylla than in susceptible D. brevis, however, glutathione S-transferase and cytochrome P-450 monooxygenase activities were similar. Esterases seem to be a major factor conferring insecticide resistance in P. pyricola.; Although the detoxification capacities of P. pyricola and D. brevis were quite similar, pear psylla has developed resistance to many insecticides in the Rogue River Valley, whereas D. brevis has remained susceptible. Biochemical factors may be important in determining the potential of resistance development, however, they are less important in determining the rate at which resistance develops. Computer simulation studies showed that life history and ecological factors are probably of greater importance in determining the rate at which resistance develops in P. pyricola and D. brevis. High fecundity and low immigration of susceptible individuals into selected populations appear to be major factors contributing to rapid resistance development in pear psylla compared with D. brevis.; Results of this study may contribute to better selective insecticide use, pesticide resistance management, and integrated control of pear psylla.