Effect of climatic factors on survival and development of legume pod borer, Helicoverpa armigera

The survival and development of legume pod borer, Helicoverpa armigera were studied at different temperatures, relative humidities and CO₂ regimes under laboratory conditions. Larval weight increased significantly with an increase in temperature from 15 (8 mg/larvae) to 35°C (398.8 mg/larvae) at 10 DAI (days after initiation of the experiment) while the larval survival showed a reverse trend and maximum larval survival was recorded at 15ºC (76%). The larval period varied between 40.2 days at 15ºC to 10 days at 35°C. Pupal weight decreased with an increase in temperature from 15 (373.8 mg/pupa) to 35°C (331.2 mg/pupa). The pupal period also decreased as the temperature increased (61.6 days at 15°C and 8.4 days at 35°C). The growth of H armigera was faster at 35°C than at 15 and 25°C (larval period 10 days, pupal period 8.4 days). Larval and pupal periods were prolonged to 40.2 and 61.6 days respectively at 15°C. Highest larval survival (67.6%) was recorded at 75 and minimum (44.09%) at 25 per cent RH but the larval period was longer at 25 (11 days) than at 50–90 per cent RH (10 to 10.2 days). There were no significant differences in pupal period and adult emergence across humidity regimes. The larval survival (67.6%), pupation (61.06%) and adult emergence (55.2%) were maximum at 75 per cent RH and the larval and pupal periods were shortest. There were no significant differences in larval weight, larval survival, larval and pupal periods, pupal weight, pupation, adult emergence and fecundity across CO₂ concentrations. Elevated CO₂ shortened the life cycle of H armigera but the fecundity increased with an increase in CO₂ concentration suggesting that elevated CO₂ will lead to rapid generation turnover and increased rates of population increase of H armigera.