Cross-resistance between benzoylureas and benzoylhydrazines in the codling moth, Cydia pomonella L.

Failure in the control of the codling moth, Cydia pomonella L., with diflubenzuron was observed for three years in several locations of southern France. A laboratory procedure was set up to screen field populations for resistance to insecticides which regulate or inhibit insect development. Last-instar larvae were captured with corrugated cardboard traps, and the tests were conducted on the F1 progeny. Newly hatched larvae were deposited in individual cups on thin layers of artificial diet, first treated with the pesticide by the way of a spray tower. They were then placed in a controlled environment chamber at 25(+/-1)degrees C. Mortality was recorded after the first moulting, i.e. five days after infestation. These tests revealed a 370-fold resistance to diflubenzuron in one population of C. pomonella. Cross-resistance was observed with the two other benzoylureas registered in France against this species: teflubenzuron (seven-fold resistance) and triflumuron (102-fold resistance). The two populations observed also presented cross-resistance (26-fold) with the ecdysone analogue tebufenozide (benzoylhydrazine), to which they had not previously been exposed. This is the first record of naturally occurring resistance to this new compound. Ovicidal tests on F3 progeny also indicated possible cross-resistance with the juvenile hormone analogue, fenoxycarb, for one strain. The resistance to these different insecticides appears to be codominant. It also proved possible to detect resistance by testing the F1 progeny of males captured with non-adhesive sex pheromone traps, paired with females of a laboratory susceptible strain.