CROSS-RESISTANCE BETWEEN AZINPHOS-METHYL AND TEBUFENOZIDE IN THE GREENHEADED LEAFROLLER, PLANOTORTRIX-OCTO

Organophosphate(OP)-resistant greenheaded leafroller, Planotortrix oct o, from Dumbarton, Central Otago, New Zealand, were tested for resista nce to tebufenozide and azinphos-methyl. Colonies of P. octo were obta ined in 1993 and 1995 by tethering virgin females of an OF-susceptible strain (S x S) in apple orchards at Dumbarton, where they mated with wild males, and then raising their progeny (S x D). To remove suscepti ble insects, first-instar larvae from these colonies were selected res pectively four and three times with discriminating doses of azinphos-m ethyl (1993-94, direct spray) to create colony S x DSe(Az), or tebufen ozide (1995-96, diet-sprayed residue) to produce S x DSe(Te). Dosage m ortality tests showed that S x D first-instar larvae were 2- to 4-time s resistant to azinphos-methyl and 5- to 8-times resistant to tebufeno zide at LD50, compared to S x S. Tests with progeny of isofemale lines of S x D revealed two groups of insects, one 3.5-times resistant and the other 14-times resistant to tebufenozide. After selection, S x DSe (Az) larvae were 14-times resistant to azinphosmethyl and 13-times res istant to tebufenozide, compared to S x S. S x DSe(Te) larvae were 21- times resistant to azinphos-methyl and 76-times resistant to tebufenoz ide. Resistance of S x DSe(Te) to tebufenozide declined from 269-times at six days to 76-times, 36 days after first exposure. All tests resu lts demonstrated the presence of resistance to azinphos-methyl and teb ufenozide in the P. octo population and high cross-resistance between these chemicals. Selection with either chemical conferred resistance t o the other. Continued use of mating disruption in a resistance manage ment programme at Dumbarton is recommended. (C) 1998 Society of Chemic al Industry.