Cross-resistance between azinphos-methyl and tebufenozide in the greenheaded leafroller,Planotortrix octo

Abstract

Organophosphate(OP)-resistant greenheaded leafroller, Planotortrix octo, from Dumbarton, Central Otago, New Zealand, were tested for resistance to tebufenozide and azinphos-methyl. Colonies of P. octo were obtained in 1993 and 1995 by tethering virgin females of an OP-susceptible strain (S ] S) in apple orchards at Dumbarton, where they mated with wild males, and then raising their progeny (S ] D). To remove susceptible insects, Ðrst-instar larvae from these colonies were selected respectively four and three times with discriminating doses of azinphos-methyl (1993È94, direct spray) to create colony S ] DSe(Az), or tebufenozide (1995È96, diet-sprayed residue) to produce S ] DSe(Te).Dosage mortality tests showed that S ] D Ðrst-instar larvae were 2-to 4-times resistant to azinphos-methyl and 5-to 8-times resistant to tebufenozide at LD 50 , compared to S ] S. Tests with progeny of isofemale lines of S ] D revealed two groups of insects, one 3É5-times resistant and the other 14-times resistant to tebufenozide. After selection, S ] DSe(Az) larvae were 14-times resistant to azinphosmethyl and 13-times resistant to tebufenozide, compared to S ] S. S ] DSe(Te) larvae were 21-times resistant to azinphos-methyl and 76-times resistant to tebufenozide. Resistance of S ] DSe(Te) to tebufenozide declined from 269-times at six days to 76-times, 36 days after Ðrst exposure. All tests results demonstrated the presence of resistance to azinphos-methyl and tebufenozide in the P. octo population and high cross-resistance between these chemicals. Selection with either chemical conferred resistance to the other. Continued use of mating disruption in a resistance management programme at Dumbarton is recommended.