Utilization of Bt Cotton hybrids in integrated pest management and their impact on non-target insects
The investigations were carried out on the farmers field at Hadagali taluk of Bellary (district) and Department of Agricultural Entomology, University of Agricultural Sciences, Dharwad during 2003-04 and 2004-05 crop seasons. Population of Helicoverpa armigera (Hubner) larvae was significantly lowest on Bt cotton (0.09 – 0.14 larvae/plant) compared to non-Bt (0.39 – 0.41 larvae/plant) and conventional cotton hybrids (0.28 – 0.40 larvae/plant). Population of sucking pests viz., leafhoppers, aphids, whiteflies and thrips, natural enemies viz., Chrysoperla, coccinellids and spiders, soil micro-arthropods and macro-organisms showed no significant differences in time and magnitude of appearance between Bt, non-Bt and conventional cotton hybrids. While, the population of red cotton bug was significantly high on Bt cotton compared to non- Bt cotton and conventional cotton hybrids. Ovipositional preferences of H. armigera and Chrysoperla carnea (Stephans) did not differ between Bt cotton or non-Bt cotton versions of the same hybrid. But, differential ovipositional preference was evident across the different cotton hybrids. So, among the cotton hybrids, RCH-2Bt which preferred less by H. armigera and more by C. carnea for oviposition can be a best option for natural enhancement of C. carnea. Tritrophic interaction studies between Bt cotton, H. armigera and larval parasitoid, Campoletis chlorideae (Uchida) indicated significant negative impact of Bt cotton hybrids on C. chlorideae parasitization at flowering stage, but not at boll maturation stage of the crop. Among the different Bt cotton hybrids evaluated, MECH-184Bt, RCH-144Bt, RCH- 20Bt and RCH-2Bt performed superior by recording lower population of H. armigera, Pectinophora gossypiella (Saunders) larvae and fruiting bodies damage and inturn recoded higher seed cotton yield (11.08, 10.33, 9.37 and 9.14 q/ha, respectively) followed by MECH- 162Bt and MECH-12Bt under un-protected conditions. However, with respect to sucking pests, MECH-184Bt and RCH-2Bt were superior. Among the different IPM modules developed and studied, Adaptable Integrated Pest Management (AIPM) and Modified Integrated Pest Management (MIPM) were equally good in suppressing bollworm complex and sucking pests and recorded lower fruiting bodies and locule damage comparable to Recommended Package of Practices (RPP) but, superior than Bio-Intensive Pest Management (BIPM). Both AIPM and MIPM modules required minimum interventions against insect pests based on economic threshold level (ETL) and conserved natural enemies comparable to BIPM. The modules, AIPM and MIPM registered higher seed cotton yield of 20.93 and 19.80 q/ha, respectively during 2003-04 and 26.58 and 25.70 q/ha, respectively during 2004-05 seasons with net returns ranging from Rs.29, 720 to 32, 194/ha can be a best option for Bt cotton cultivation.
UAS Dharwad
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