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Abstract: The geographical variability in Helicoverpa armigera susceptibility levels to Cry2Ab toxin expressed by transgenic maize (not currently commercialized in India) was determined through log dose probit assays conducted on populations collected during 2004–05 (from 25 districts) and 2007–08 (from 22 districts) across India. While 2004–05 is the year prior to commercialization of dual gene Bollgard-II-Bt cotton that expresses Cry2Ab in addition to Cry1Ac, 2007–08 is two years after its commercial release. LC50 values ranged from 6.0 to 28.6 μg Cry2Ab/ml of diet in 2004–05 and from 2.46 to 34.7 μg Cry2Ab/ml of diet in 2007–08. The IC50 range in 2004–05 and 2007–08 was from 0.31 to 2.3 μg/ml and 0.10–3.4 μg/ml of diet, respectively. The probit analysis data of 2004–05 can be used as baseline indices to monitor for changes in the H. armigera susceptibility to Cry2Ab, subsequent to the introduction of Bollgard-II cotton in India. The probit analysis data of 2007–08 showed that the baseline has not undergone any significant changes two years after cultivation of Bollgard-II in India. The relatively low toxicity of Cry2Ab and its higher expression late in the cotton season compared with Cry2Ab, compounded with its presence in Bt hybrids on a separate linkage group from Cry1Ac suggest problems of resistance in the future. [Copyright &y& Elsevier]

Abstract: The mode of inheritance of resistance to Cry1Ac toxin of Bacillus thuringiensis in the cotton bollworm, Helicoverpa armigera (Hübner), was elucidated through bioassay analysis of the response of resistant, susceptible, F1 hybrid and backcross H. armigera progeny to Cry1Ac using semi-synthetic diet and transgenic Bt cotton plants. The dominance value estimates ranged between 0.42 and 0.57. Resistance was found to be monogenic, autosomal and inherited as a semi-dominant trait. Genetic studies of response of H. armigera to transgenic Bt cotton showed that the effective resistance on transgenic Bt cotton plants was also inherited as a semi-dominant trait. [Copyright &y& Elsevier]

The semilooper, Anomis flava Fab is a foliage feeding lepidopteran insect, often found occurring in the cotton ecosystem during the first 60–75 days of sowing. Its occurrence overlaps or just precedes the incidence of Helicoverpa armigera. This study reports the impact of mechanical wounding or of prior herbivory by semilooper larvae on cotton host-plant resistance to H. armigera. It is proposed that cotton plant damaged by semilooper or by mechanical means is less preferred for the growth of H. armigera. This is probably due to a reduction in the nutritive quality, induction of allelochemicals, such as chlorogenic acid and of oxidative enzymes, such as lipoxygenases and peroxidases in the damaged plants. [Copyright &y& Elsevier]

Insecticide resistance to representatives of commonly used insecticide groups (pyrethroids—cypermethrin; organophosphates—chlorpyriphos; cyclodienes—endosulfan) was determined in five major insect pests of cotton from the main cotton growing regions of India with emphasis on Andhra Pradesh and Maharashtra. The cotton bollworm Helicoverpa armigera (Hubner) exhibited widespread resistance to cypermethrin with 23–8022-fold resistance being recorded in field strains. Resistance to endosulfan and chlorpyriphos was low to moderate in H. armigera. The overall resistance of the pink bollworm Pectinophora gossypiella (Saunders) to pyrethroids was low. However, high resistance levels of 23–57-fold to endosulfan were recorded in some areas of Central India. Resistance to chlorpyriphos was high in the Medak, Bhatinda and Sirsa strains from North India. The majority of the Spodoptera litura (Fab.) strains collected in South India exhibited high resistance levels of 61–148-fold to cypermethrin. Resistance to endosulfan was high only in two strains, collected from Bhatinda and Karimnagar in North India. The S. litura strains from South India exhibited high levels of resistance at 45–129-fold to chlorpyriphos. Insecticide resistance in Earias vittella (Fab.) was low to moderate in the Sirsa and Sriganganagar strains from North India. Bemisia tabaci (Genn.) exhibited moderately high levels of resistance to cypermethrin, but resistance to endosulfan and chlorpyriphos was negligible in the field strains tested. The implications of resistance for cotton pest management in India are discussed. [Copyright &y& Elsevier]

The baseline toxicity of Cry1A δ-endotoxins (derived from Bacillus thruringiensis (Kurstaki)) on field populations of the cotton bollworm, Helicoverpa armigera (Hub.), was determined through log dose probit analysis. All the three Cry1A proteins were found to be toxic to the bollworm larvae. Cry1Ac was found to be the most toxic followed by Cry1Aa andCry1Ab. LC[sub 50] values ranged from 0.07 to 0.99 μg/ml(14- fold) for Cry1Aa, 0.69 to 9.94 μg/ml (14-fold) for Cry1Ab and 0.01 to 0.67 μg/ml of diet (67-fold) for Cry1Ac. The LC[sub 50] values deduced from the cumulative log dose probit response of the data pooled from all assays, were 0.62 μg/ml for Cry1Aa, 4.43 μg/ml for Cry1Ab and 0.100 μg/ml of diet for Cry1Ac. The respective LC[sub 50] values represent the baseline susceptibility indices for resistance monitoring through the conventional log dose probit assays. The LC[sub 99] values derived from the cumulative data were 515 μg/ml for Cry1Aa, 13385 μg/ml for Cry1Ab and 75 μg/ml of diet for Cry1Ac. These values represent the diagnostic doses for routine monitoring of resistance to the respective toxins through discriminating dose assays after the introduction of Bt transgenic crops. [ABSTRACT FROM AUTHOR]