Genetic analysis of resistance to azinphosmethyl in the pear psylla Cacopsylla pyri

Laboratory selection with azinphosmethyl had little effect on the chemical resistance in Cacopsylla pyri strains, in comparison to the original wild p opulations. The resistance ratio relative to a susceptible strain varied fr om 10- to 40-fold depending on the generation studied. Crosses between two resistant strains and the susceptible strain show resistance to be autosoma lly inherited and semi-dominant in expression. Backcrosses between F1 and t he susceptible strain were unable to distinguish unabigously between monoge nic and polygenic inheritance. In the majority of experiments, however, the overall dose-response relationship for backcross progeny was consistent wi th a single gene hypothesis. Additional bioassays showed azinphosmethyl-res istant strain to cross-resistant monocrotophos and phosmet, but not carbama tes, pyrethroids, amitraz or the organophosphates chlorpyrifos and mevinpho s.