Isolation and characterization of Lepidoptera specific Bacillus thuringiensis strains predominantly from north-eastern states of India.

Both, the tobacco caterpillar Spodoptera litura (Fabricius) and the cotton bollworm Helicoverpa armigera (Hibner), are serious polyphagous pests causing considerable loss to crops. Indiscriminate use of chemical pesticides for controlling them has rather resulted in their resistance development. Microbial pesticides, Bacillus thuringiensis in particular, play an important role in pest management. Here, we isolated Bacillus thuringiensis-like bacteria from the soil samples primarily collected from North East region of India along with some states viz., Haryana, Punjab, Maharashtra, West Bengal and Uttarakhand and studied their toxicity against the above two insect pests at 10 gg/g along with standard strain B. thuringiensis subsp. kurstaki HD-I and at 1 pg/g Pseudomonasfluorescens based MVPII expressing CrylAc toxin and AUG-5. Isolates AUG-5 and GTG-7 proved toxic to more than 75% larvae on the 4h as well as 7h day of the treatment of the neonates of H. armigera. The AUG-5 isolate was also effective against S. litura. Ten effective isolates (AUG-5, GTG-4, GTG-7, GTG-9, GTG-42, GTG-64, GTG-70, GTG-3S, GTG-4S and GTG-6S) were characterized using biochemical and 16S rDNA analysis. Nearly, all the isolates tested positive for utilizing monosaccharides. All selected B. thuringiensis isolates showed resistance to ampicillin and co-trimoxazole except AUG-5 to- co-trimoxazole. AUG-5 and GTG-7 were highly toxic to both insects, and possessed cryl, cry1A and cry2 genes. These isolates AUG-5 and GTG-7 also contained high CrylAc (104.8 and 88.32 ng/mg) and Cry2Ab (3792 and 1305.9 ng/mg), respectively in their spore-crystal complex. Both, AUG-5 and GTG-7 isolates, could be considered for further development as bioinsecticides. The present study has established the diversity and richness of B. thuringiensis-like isolates in soils collected from north-eastern region of India.

Inheritance of Cry1Ac resistance and associated biological traits in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae).

The analysis of reciprocal genetic crosses between resistant Helicoverpa armigera strain (BH-R) (227.9-fold) with susceptible Vadodara (VA-S) strain showed dominance (h) of 0.65-0.89 and degree of dominance (D) of 0.299-0.782 suggesting Cry1Ac resistance as a semi-dominant trait. The D and h values of F(1) hybrids of female resistant parent were higher than female susceptible parent, showing maternally enhanced dominance of Cry1Ac resistance. The progeny of F(2) crosses, backcrosses of F(1) hybrid with resistant BH-R parent did not differ significantly in respect of mortality response with resistant parent except for backcross with female BH-R and male of F(1) (BH-RxVA-S) cross, suggesting dominant inheritance of Cry1Ac resistance. Evaluation of some biological attributes showed that larval and pupal periods of progenies of reciprocal F(1) crosses, backcrosses and F(2) crosses were either at par with resistant parent or lower than susceptible parent on treated diet (0.01 microg/g). The susceptible strain performed better in terms of pupation and adult formation than the resistant strain on untreated diet. In many backcrosses and F(2) crosses, Cry1Ac resistance favored emergence of more females than males on untreated diet. The normal larval period and the body weight (normal larval growth) were the dominant traits associated with susceptible strain as contrast to longer larval period and the lower body weight (slow growth) associated with resistance trait. Further, inheritance of larval period in F(2) and backcross progeny suggested existence of a major resistant gene or a set of tightly linked loci associated with Cry1Ac sensitivity.

Governing evolution: A socioecological comparison of resistance management for insecticidal transgenic Bt crops among four countries.

Cooperative management of pest susceptibility to transgenic Bacillus thuringiensis (Bt) crops is pursued worldwide in a variety of forms and to varying degrees of success depending on context. We examine this context using a comparative socioecological analysis of resistance management in Australia, Brazil, India, and the United States. We find that a shared understanding of resistance risks among government regulators, growers, and other actors is critical for effective governance. Furthermore, monitoring of grower compliance with resistance management requirements, surveillance of resistance, and mechanisms to support rapid implementation of remedial actions are essential to achieve desirable outcomes. Mandated resistance management measures, strong coordination between actors, and direct linkages between the group that appraises resistance risks and growers also appear to enhance prospects for effective governance. Our analysis highlights factors that could improve current governance systems and inform other initiatives to conserve susceptibility as a contribution to the cause of public good.

Differential toxicity of Bacillus thuringiensis strains and their crystal toxins against high-altitude Himalayan populations of diamondback moth, Plutella xylostella L.

BACKGROUND: Diamondback moth, Plutella xylostella (L.), is a major insect pest of crucifers in the biodiversity-rich north-western Indian Himalayan hills. The present investigation was aimed at determining the susceptibility pattern of P. xylostella populations collected from different locations of this region to autochthonous and standard Bacillus thuringiensis strains. RESULTS: Among the reference as well as indigenous B. thuringiensis strains tested, sub spp. kurstaki HD-1, kurstaki HD-73, galleriae HD-8, local galleriae/colmeri strain BtOa1 and some of their Cry1 class toxins were found to be highly toxic. Surprisingly, the sub sp. tolworthi HD-125, local tolworthi strain BtHa1 and Cry9 class toxins were found to be non-toxic. Midgut homogenate from fourth-instar larvae was found to activate 130 kDa protoxin from the local tolworthi strain BtHa1 into 68 kDa toxin, but failed to exert any larval mortality, probably owing to lack of receptor binding. CONCLUSION: The present study provides valuable baseline susceptibility data for the deployment of B. thuringiensis-based control methods, as well as for future monitoring of development of resistance in P. xylostella to B. thuringiensis in this ecologically sensitive region.

Field-evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India.

BACKGROUND: The pink bollworm is one of the most destructive pests of cotton. Transgenic cotton producing Bt toxin Cry1Ac or a combination of Cry1Ac and Cry2Ab2 has been used effectively against this pest. However, some other insects have evolved resistance to Bt toxins in the field. During the 2007-2008 and 2008-2009 seasons, pink bollworm populations in India were surveyed to evaluate their responses to Cry1Ac and seed powder containing Cry1Ac and Cry2Ab2. RESULTS: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non-Bt cotton in the Amreli district of Gujarat in western India. The median lethal concentration of Cry1Ac for five-day-old larvae (LC50 ) was significantly higher for insects derived in 2008 from Amreli than for any of the other field populations tested from four locations in India. For Cry1Ac, the mean LC50 for the strain derived from Amreli in 2008 was 44 times higher than for the most susceptible population. However, for seed powder of Bollgard II containing primarily Cry2Ab2, the 2008 Amreli population was only slightly less susceptible than the most susceptible population. CONCLUSIONS: The data reported here constitute the first evidence of field-evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009-2010 growing season, which confirmed field-evolved resistance to Cry1Ac in Amreli. The lack of cross-resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac.