Pyrethroid Resistance in Field Populations of Heliothis virescens (Lepidoptera: Noctuidae) in Mississippi in 1986

Laboratory bioassays of Heliothis virescens (F.) larvae from strains collected from cotton and soybeans in Mississippi during 1986 showed LD50’s 5- to 15- and 18- to 23- fold higher for fenvalerate and cypermethrin, respectively, than those obtained from a susceptible laboratory colony. Bioassays of third instars on cotton terminal buds treated with recommended field application rates of fenvalerate and cypermethrin indicated that these resistance levels resulted in 40–56% reductions in mortality of third instars compared with those obtained with a susceptible strain. Similar results were obtained in bioassays of a strain from Texas.