Resistance to insecticides in winter‐ and summer‐forms of pear psylla, Psylla pyricola

Abstract

AbstractSummer‐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.