Determination of Thermal Constants and Developmental Thresholds for Gram Pod Borer, Helicoverpa Armigera (Hübner) (Lepidoptera: Noctuidae)

Development and survival of Gram pod borer, Helicoverpa armigera eggs, larvae and pupae were studied at each of eight constant temperatures: 12±1, 15±1, 18±1, 21±1, 24±1, 27±1, 30±1 and 33±1 °C, in incubators. The survival from 1st instar to adult emergence ranged between a maximum of 90% at 27°C and 30% at 18°C and 33°C. Developmental duration of different larval instars and pupae declined with an increase in temperature from 12 to 33 °C. The optimum temperature for the survival and development of H. armigera was observed to be 27°C. Oviposition did not occur at 15°C and 18°C as either adult did not emerge or they died before oviposition. The relationship between temperature (T) and development rate (r) was determined using linear regression to estimate the thermal constant (K) and development threshold (T0). Thermal constant for egg stage was 35.3-degree days (DD) with 16.9oC as developmental threshold. Likewise, thermal constant for 1st to 6th larval instars and pupal stage were computed as 50.0, 45.5, 62.5, 47.6, 52.6, 47.6 and 166.7 DD, respectively, with corresponding development thresholds as 12.1, 11.3, 10.4, 12.0, 11.8, 13.9 and 16.0 oC. Single developmental threshold for larval stage was computed as 14.3oC. These thermal constants and threshold of development can be used in mechanistic population simulation models of pest, which in turn will facilitate the assessment of climate change impact on the pest.