Van De Baan_1991_Pest.Sci_32_225

Summer-form pear psylla, Psylla pyricola Foerster, from sprayed pear were resistant to endosulfan (2.4-fold), methiocarb (2.5-fold), ethylan (5.8-fold), azinphos-methyl (7.7-fold), and fenvalerate (40.1-fold). Esterase (3.8-fold), glutathione transferase (1.8-fold), and cytochrome P-450 monooxygenase (1.6-fold) detoxification enzyme activity was higher in resistant than in susceptible summer forms. Synergism by piperonyl butoxide and S,S,S-tributylphosphorotrithioate (DEF) was added evidence for cytochrome P-450 monooxygenases and esterases as resistance mechanisms. Reduced penetration may also have contributed to resistance, as indicated by a 1.6-fold slower penetration of azinphos-methyl in resistant than susceptible summer-forms. Similar differences in insecticide toxicity and esterase and glutathione transferase activities were observed between winter-forms of resistant and susceptible pear psylla. Winter-forms of P. pyricola were up to three times more tolerant to insecticides than summer-forms. Higher cytochrome P-450 monooxygenase activity (1.7-fold) and slower azinphosmethyl penetration (2.1-fold) in winter-forms may have contributed to their greater insecticide tolerance; however, sequestration may also have been involved.