Search

Ten isolates of entomopathogenic nematode (EPN) Heterorhabditis indica were evaluated for their differential infectivity against two major cotton insect pests viz., Helicoverpa armigera and Spodoptera litura. The results of bioassay revealed that the third instar larvae of H. armigera were relatively more susceptible to the EPN isolates compared to the larvae of S. litura. All the ten EPN isolates could reproduce successfully on H. armigera larvae however, the isolates viz., CICR-Su and CICR-SUB exhibited relatively higher virulence. On the other hand, on S. litura larvae only one isolate- CICR-BBFNS2 was able to produce infective juveniles and the rest failed to do so. Analysis of haemolymph composition of EPN infected H. armigera and S. litura larvae indicated the phase change of bacterial symbionts as a primary reason for the failure of EPN to reproduce and multiply in S. litura larvae. Higher percentage of primary phase colonies of bacterial symbionts were recorded in H. armigera larvae which resulted in successful progeny production of EPN while secondary phase colonies were predominant in the larvae of S. litura which resulted in failure of EPN isolates to reproduce. Phylogenetic tree made using internal transcribed spacer (ITS) region of ribosomal DNA of nematodes and 16sRNA of bacterial symbionts revealed the distinctness and uniqueness of the EPN isolate CICR-BBFNS2 which was able to multiply on the larvae of both H. armigera and S. litura from rest of the nine isolates which could multiply only in H. armigera. The results indicate that isolate CICR-BBF-NS2 has potential for deployment in IPM programme for management of H. armigera and S. litura. [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]