Bioassay of hexaflumuron,an insect growth regulator and its cross resistance in cotton bollworm, Helicoverpa armigera

Three methods for the bioassay of hexaflumuron were compared for Helicoverpa armigera and its cross resistance was assessed.In the foliar residue and diet incorporation tests,larvae of the 1st instar were very susceptible to hexaflumuron.The 2nd,3rd,4th and 5th instar larvae were slightly less susceptible than the 1st instar larvae and the 6th instar larvae much less.The chemical also had high toxicity to the 3rd and 4th instar larvae in the topical application test.As a quick,reliable technique,the foliar residue test was the most suitable bioassay for insect growth regulator (IGR),with the 1st instar larvae,at least 48 h of exposure period and 5 days after treatment (DAT) of observation time.Results also showed there was no cross resistance to hexaflumuron in two fenvalerate resistant field strains.Piperonyl butoxide (PBO) had a dose dependent effect on hexaflumuron toxicity,i.e.synergistic at low dosages,but antagonistic at high dosage.