Spectrum of insecticide resistance in Cydia pomonella (Lepidoptera: Tortricidae) in southeastern France

Strains of codling moth, Cydia pomonella (L.), were collected from 3 orchards in southeastern France where different strategies of chemical control had failed. Males were mated with females of a susceptible laboratory strain and the progeny were maintained for 7-9 generations on artificial diet treated with deltamethrin, diflubenzuron, or a mixture of diflubenzuron and phosalone. These insecticides were choosen to prolong the selection pressure to which each had previously been exposed in the field. Susceptibility to these compounds and to azinphosmethyl were evaluated on newly hatched larvae every 2nd generation and compared with a susceptible laboratory strain. Resistance to diflubenzuron, deltamethrin, and phosalone occurred in the strain obtained from the orchard protected mainly with pyrethroids during the last 5 yr. Selecting this strain with deltamethrin for 7 generations resulted in a 96-, 6- and 3-fold increase in the resistance to diflubenzuron, deltamethrin, and phosalone, respectively. This reveals a cross-resistance to these different insecticides in this selected strain, which also exhibited a resistance to teflubenzuron, tebufenozide, bifenthrin, and lambda-cyalothrin. Selection with diflubenzuron also resulted in a high resistance to diflubenzuron but a lower resistance to pyrethroids compared with the strain selected with deltamethrin. A decreased efficacy of azinphos methyl was observed on the 3 selected strains. The simultaneous resistance to several classes of insecticides in these codling moth populations suggests that the implementation of a rotation program to delay resistance development will be difficult, and points to the need for improving alternative control methods such as microbiological insecticides or mating disruption.