Feeding disruption bioassay for species and Bacillus thuringiensis resistance diagnosis for Heliothis virescens and Helicoverpa zea in cotton (Lepidoptera: Noctuidae)

Bioassay methodology was developed for species diagnosis of Heliothis virescens compared with Helicoverpa zea in cotton and to detect H. virescens larvae with significant levels of resistance to the biopesticide, Bacillus thuringiensis. The assay end-point is feeding disruption, which is measured by a lack of fecal production by larvae exposed to a diagnostic dose of CryIAc in a blue indicator diet. In laboratory tests, the bioassay accurately distinguished neonates of H. zea from H. virescens and was able to detect B. thuringiensis resistance in H. virescens. The assay is rapid compared with mortality assays and should be inexpensive. The assay should also be adaptable to current cotton integrated pest management programs and sampling techniques and detect most physiological mechanisms of B. thuringiensis resistance. The potential utility of the feeding disruption assay in cotton integrated pest management and with other crops, insect pests and insecticides is discussed. The studies reported here were conducted on laboratory strains of B. thuringiensis susceptible H. virescens and H. tea and a highly B. thuringiensis-resistant laboratory strain of H. virescens (YHD2) originally collected in North Carolina. (C) 1998 Elsevier Science Ltd. All rights reserved