Bhamare, V.K.Thakre, Bhushan Ashokrao2022-08-222022-08-222020-09-3021127https://krishikosh.egranth.ac.in/handle/1/5810186578The investigations on the survival and development of bollworms and expression of Cry toxins in public sector Bt cotton hybrids were carried out at the Post Graduate Laboratory, Department of Agricultural Entomology, College of Agriculture, Latur (VNMKV, Parbhani), Maharashtra (India) during 2019-20. The survival and development of bollworm larvae was observed instar wise on leaves, squares, young bolls and mature bolls of different public sector Bt cotton hybrids (NHH-44 BG II, PKV Hy-2 BG II, PDKV-JKAL-116 BG II, G. COT-10 Hy. BG II, G. COT-08 Hy. BG II and NHH-44 non-Bt as control) at 60-80, 90-110, 120-140 and 150-170 days old crop, respectively. The different survival and developmental parameters such as larval mortality, larval weight, pupation, pupal weight, adult emergence, growth and survival indices of the survived larvae after releasing on different plant parts of different public sector Bt cotton hybrids at pre-determined intervals were observed. The laboratory bioassay was carried out to study the survival and development of H. armigera and S. frugiperda on different public sector Bt cotton hybrids and evidenced that the larval mortality of early instar H. armigera and S. frugiperda larvae on leaves, squares, young bolls and mature bolls of different public sector Bt cotton hybrids was higher than the later instars. Whereas, the late instar larvae survived on plant parts of all public sector Bt cotton hybrids exhibited adverse effects on the growth and developmental biology of insects, such as reduced larval weights with deformities, prolonged duration for larval development, diminution in pupation, formation of small pupae exhibiting lower weight, reduction in per cent adult emergence with low growth and survival indices for H. armigera and S. frugiperda. The growth and survival index values were lower for the larvae reared on leaves and squares as compared to those reared on young bolls and mature bolls of different public sector Bt cotton hybrids. The laboratory bioassay was conducted to study the survival and development of E. vittella and P. gossypiella on different public sector Bt cotton hybrids and revealed that the larval mortality of the early instar E. vittella larvae on squares and young bolls and the larval mortality of early instar P. gossypiella larvae on mature bolls of different public sector Bt cotton hybrids was higher compared to the later instars. While, the late instar larvae of both E. vittella and P. gossypiella survived on plant parts of different public sector Bt cotton hybrids exhibited very diminutive effects on the growth and developmental biology of insects, such as reduced larval weights, prolonged larval developmental period, reduction in pupation, formation of small pupae having less weight, diminution in per cent adult emergence with small size and unevenly developed body parts of adult and low growth and survival indices. The studies on the expression of Cry toxins on different plant part and growth stages of public sector Bt cotton hybrids (leaves, squares, young bolls and mature bolls at 60, 90, 120 and 150 days, respectively) proved that the expression of Cry toxins (Cry 1Ac and Cry 2A) significantly varied among the plant parts and growth stages of different public sector Bt cotton hybrids. The concentration of Cry 1Ac and Cry 2A toxin ranged significantly from 2.59 to 4.71 and 8.18 to 13.15 μg per g fresh tissue, respectively in leaves of different public sector Bt cotton hybrids at 60 days old crop. The concentration of Cry 1Ac and Cry 2A toxin varied significantly from 2.58 to 3.73 and 14.32 to 15.96 μg per g fresh tissue, respectively in squares of different public sector Bt cotton hybrids at 90 days old crop. The concentration of Cry 1Ac and Cry 2A toxin ranged significantly from 0.67 to 1.47 and 4.25 to 6.40 μg per g fresh tissue in young bolls of different public sector Bt cotton hybrids at 120 days old crop, respectively. While, the concentration of Cry 1Ac and Cry 2A toxin varied significantly from 0.028 to 0.33 and 1.77 to 4.82 μg per g fresh tissue in mature bolls of different public sector Bt cotton hybrids at 150 days old crop, respectively. Significantly highest Cry toxin expression was observed in leaves and squares compared to young bolls and mature bolls. Cry toxin levels were also decreased with the advancement in crop age. A progressive decline in the expression of cry toxins was observed throughout the growing season among all the public sector Bt cotton hybrids with the age and active growth of the plant. Among the different public sector Bt cotton hybrids, NHH-44 BG II evidenced significantly superior results over rest of Bt cotton hybrids.EnglishThesis