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Title: Diapause, cold-hardiness and flight ability of Cry1Ac-resistant and -susceptible strains of Helicoverpa armigera (Lepidoptera: Noctuidae)

item Rector, Brian

Submitted to: European Journal of Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2007
Publication Date: 10/15/2007
Citation: Liang, G., Wu, K., Rector, B.G., Guo, Y. 2007. Diapause, cold-hardiness and flight ability of Cry1Ac-resistant and -susceptible strains of Helicoverpa armigera (Lepidoptera: Noctuidae). European Journal of Entomology. 104:699-704.

Interpretive Summary: The Old World cotton bollworm, Helicoverpa armigera, is a major pest of cotton and maize and is closely related to the New World cotton bollworm, H. zea. These insects are among those targeted by Bacillus thuringiensis (Bt)-based insect pest management tools, including transgenic Bt crops. One of the major concerns surrounding Bt crops is the development of resistance to Bt toxins in wild populations of pest insects. Such resistance has been observed in wild populations of a few species, as well as in laboratory-reared populations of other species, including H. armigera. In this study, laboratory populations of Bt-resistant and -susceptible H. armigera were compared for a number of physiological traits related to the insect's ability to overwinter and expand its geographical range. The results indicate that Bt-resistant H. armigera may be better suited to surviving through cold winters than normal, wild-type H. armigera.

Technical Abstract: The diapause inducement condition, cold hardiness, and flight ability in Cry1Ac-resistant (BtR) and Cry1Ac-susceptible (96S) strains of Helicoverpa armigera (Hübner) were compared in the laboratory. The BtR strain was derived from the 96S strain and shows 1375-fold resistance to the Cry1Ac toxin after having been selected for 52 generations. Compared with the 96S strain, the Bt-resistant strain was more likely to go into diapause under a short-photoperiod environment. At 11:13, 12:12, 13:11 (light:dark) photoperiods, the percentages of BtR insects entering diapause were 72.7%, 82.9% and 68.7%, respectively, which were significantly higher than those in the 96S strain (58.6%, 67.4% and 46.3%, respectively) under the same conditions. The supercooling points (SCP) and freezing points (FP) were not significantly different between the BtR and 96S strains. The LT50 (50% lethal time) and LT90 (90% lethal time) of BtR pupae were also not significantly different from those of the 96S strain at -15°C. The moths from both strains had similar flight ability when their larvae were fed with nontoxic control diet. The total flight distance of these moths was 57.5 Km whose larvae fed on normal diet, which was more than twice as much as for those feeding on Bt diet (26.2 Km). Flight duration for these moths was longer after feeding on normal diet (10.6 h) than after feeding on Bt diet (7.3 h).