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Bt cotton plants, with bollworm resistant trait, have been widely adopted since introduced in India in 2002. As a proactive measure to prevent evolution of resistance to Bt protein(s), it was approved for commercial cultivation with a stipulation of structured refuge of minimum 20% of the Bt area, constituted by plants that do not produce Bt toxins and thus allow growth and development of population of Bt susceptible pests. Though the refuge cotton seeds are provided in a separate pouch within each Bt cotton seed packet, Indian farmers have been reluctant to sow refuge. To find out a method for ensured refuge planting, we experimented with 'built-in-refuge' (BIR) in which non-Bt cotton seeds were blended with Bt cotton seeds in various proportions ie 5,10, 50% along with 20% recommended structured refuge and each treatment was evaluated in terms of fruiting body damage by major cotton lepidopterans, relative to the regulator stipulated 20% non-Bt structured refuge at five locations during cotton growing season of 2012–13. A major outcome from this study was that treatments with 5 and 10% non-Bt blends with bollga0rd-II were as effective as the 20% structured refuge, based on fruiting body damage due to bollworms, a key factor in managing Bt resistance without any compromise to the seed cotton yield. It can be concluded that the seed blend technology is a good option to impose refugia compliance to delay resistance in Bt cotton to bollworms in a country having lesser alternate hosts available for the target bollworms during the season and voluntary compliance of refuge is absent. [ABSTRACT FROM AUTHOR]

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]

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]

Pink bollworm, Pectinophora gossypiella (Saunders) infestation on Bt cotton is a major concern to cotton production in India. The genetic diversity and phylogeographic structure of the insect in light of PBW resistance needs to be revisited. The objective of this study was to identify different haplotypes of pink bollworm and their distribution in India. To achieve this we studied the population structure in 44 cotton growing districts of India. The partial mitochondrial COI sequence analyses of 214 pink bollworm populations collected from 44 geographical locations representing 9 cotton growing states of India were analysed. Genetic diversity analysis exhibited presence of 27 haplotypes, among them Pg_H1 and Pg_H2 were the most common and were present in 143 and 32 populations, respectively. Distributions of pairwise differences obtained with partial COI gene data from the overall Indian populations are unimodal, suggesting population expansion in India. Significant neutrality test on the basis of Tajima' D and Fu's Fs presented a star-shaped haplotype network together with multiple haplotypes. The unimodal mismatch distribution, rejection of neutrality test with significant negative values supported the theory of demographic expansion in cotton pink bollworm populations in India. Genetic data not only provides us with a perspective of population genetics, but also that the two populations of pink bollworm, those occurring early in the season are genetically close to the late season populations with respect to their partial CO1 region. Resistance to Cry toxins does not seem to have had an impact on this region of the mt DNA in populations of pink bollworm.

Background: Pink bollworm (PBW) adaptation to transgenic Bacillus thuringiensis (Bt) cotton expressing crystal 1Ac (Cry1Ac) (Bt-I) and Cry1Ac + Cry2Ab (Bt-II) was assessed in India during 2010-2017 in 38 districts of the 10 major cotton-growing states., Results: PBW larval incidence on Bt cotton was nil in northern India, wherein the resistance ratios (RRs) to Cry1Ac were 26-262 and those to Cry2Ab were 1-108. In central and southern India, the annual average PBW larval recovery from Bt II cotton was high at 28.85-72.49% during 2014-2017. In central and southern India, the 50% lethal concentration (LC 50 ) of Cry1Ac increased from a mean of 0.330 µg mL -1 (range 0.126-0.849 µg mL -1 ) in 2013 to a mean of 6.938 µg mL -1 (range 3.52 to 10.30 µg mL -1 ) in 2017 and the RR increased from a mean of 47.12 (range 18-121) in 2013 to a mean of 1387 (704-2060) in 2017, whereas the LC 50 value for Cry2Ab increased from a mean of 0.014 µg mL -1 (range 0.004-0.094 µg mL -1 ) in 2013 to a mean of 12.51 µg mL -1 (range 3.92 to 28.10 µg mL -1 ) in 2017 and the RR increased from a mean of 5.4 (range 1-31) in 2013 to a mean of 4196 (1306-9366) in 2017., Conclusion: High PBW larval recovery on Bt-II in conjunction with high LC 50 values for Cry1Ac and Cry2Ab in major cotton-growing districts of central and southern India provides evidence of field-evolved resistance in PBW to Bt-I and Bt-II cotton. © 2018 Society of Chemical Industry., (© 2018 Society of Chemical Industry.)

A survey was conducted in 47 locations in nine cotton-growing states of India to identify the composition of mealybug species occurring on cotton. Results of the taxonomic study showed that two mealybug species, the solenopsis mealybug, Phenacoccus solenopsis (Tinsley), and the pink hibiscus mealybug, Maconellicoccus hirsutus (Green), were found to infest cotton plants from all nine cotton growing states of the country. However, P. solenopsis was found to be the predominant mealybug species, comprising 95% of the samples examined. P. solenopsis, which was hitherto not reported to occur in India, now appears to be widespread on cotton in almost all cotton-growing states of the country. P. solenopsis is an exotic species originated from the USA and was reported to damage cotton and crops of 14 families. This report discusses the implications of the introduction of this exotic polyphagous pest species and the necessary steps to mitigate its potential threat to agriculture in India.