Susceptibility of Cacopsylla pyri and C. pyricola (Homoptera: Psyllidae) to Avermectin B1 Applied Topically and as Residues on Pear Foliage

Effects of avermectin B1 were determined by topical application for Cacopsylla pyri (L.) adults in Europe and by exposure to treated pear foliage for C. pyricola (Foerster) adults and nymphs in North America. Data were obtained for mortality and egg production by survivors. With C. pyri, probit regressions for males and females were similar, summer adults were more susceptible than winter adults. Age of summer adults at treatment did not affect slope, and mortality associated with time between treatment and evaluation increased linearly up to 72 h. Avermectin B1 reduced average daily oviposition and total egg production in C. pyri. Oviposition rate was affected more in summer females than in winter females. Slopes for dose- and concentration-mortality data were similar for the two species with the two exposure techniques. The technique of exposing nymphs to treated pear leaves was also used to measure residual activity of avermectin B1 in pear foliage. Applications at 7.5 mg/liter produced Comparable mortalities for ≈1 wk longer than did half that concentration. Data derived from these tests can serve as baselines for detecting changes in susceptibility of psyllid populations, and techniques reported here could be used to detect resistant populations. Implications of these data to the development of a use strategy for avermectin B1 against psyllids attacking pear are presented.