Resistance to insecticides in a Thailand strain of Heliothis armigera (Hubner) (Lepidoptera: Noctuidae)

Bioassays were conducted with a range of insecticides to assess the degree of resistance in a strain of Heliothis armigera (Hubner) collected from the field in Thailand. A susceptible laboratory strain which had LD50's similar to those of susceptible field populations was used as a reference strain for comparisons. The Thailand strain had high levels of resistance at LD50's--resistance factors of 102-fold to cis-cypermethrin, 82-fold to trans-cypermethrin, 51-fold to fenvalerate, 125-fold to DDT and 28-fold to carbaryl. The strain had 2-fold resistance to diazinon, monocrotophos and endosulfan. These results suggest strong cross-resistance between the pyrethroids and DDT