SELECTION FOR MONOCROTOPHOS RESISTANCE IN PEAR PSYLLA, CACOPSYLLA-PYRI (L) (HOM, PSYLLIDAE)

Pear psylla, Cacopsylla pyri (L.), adults collected from commercial pe ar orchards around Toulouse (France) were selected in the laboratory f or resistance to monocrotophos. Resistance was obtained only when the insecticide selection pressure was continuous, but when some generatio ns were not selected, resistance did not develop or even reverted. Res istance appeared to be stable after 30 generations of selection and st abilized at a level of 140-fold. The monocrotophos-selected strain was highly cross-resistant to the organophosphate phosmet (155-fold) and cross-resistant to the formamidine amitraz (14-fold).