Activity of two groups of insect growth regulators,IGRs to cotton bollworm Helicoverpa armigera:

Symptom,toxicity and mode of action of insect growth regulators (IGRs),hexaflumuron,tebufenozide and RH5849,to cotton bollworm, Helicoverpa armigera (Hubner) were observed and assessed.After treated topically by hexaflumuron,the 3 instar larvae tend to move slowly with little sensitivity to a stimulate,fed on litter food an eventually die with the thin integument and a white transparent prominence on head.Some dead larvae become black and show failure of molt.The 3 instar larvae treated by RH5349 are also inactive in moving and feeding,dead larvae are in black and shrunken bodies,and living larvae abnormally molt in advance.After treated by the mixture of two chemicals,some larvae show the poisoning symptom of hexaflumuron,others are the symptom of RH5849,whereas a few larvae show mixed symptom.Hexaflumuron has a high contact toxicity to cotton bollworm,with 0.7434 μg a.i./larva of LD 50 in topical application test,and a high stomach toxicity with 2.0592 mg/L of LC 50 in leaf dipping bioassay.Tebufenozide is also stomach poisoning with 25.2576 mg/L of LD 50 ,but RH5849 has little contact poison with more than 39.3633 μg a.i./larva of LC 50 . In the mixture with different ratios ,hexaflumuron and tebufenzide are independent in action to the bollworm except the ratio of hexaflumuron 1 mg/L and tebufenozid 5 mg/L that tends to be synergistic.