Effect of thermoperiod on the regulation of diapause in Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Higher incidence of diapause in larvae of Helicoverpa armigers was recorded when larvae were exposed to thermophotoperiods with cryophase of 20 to 25°C, than under thermoperiods during constant darkness. On the otherside, larvae exhibited significantly lower percentage of dispause when exposed to cryophases lower than 20°C under thermo or thermophotoperiodic conditions. Significantly shorter time was also needed for diapause development after exposure of diapausing larvae to continuous light than to continuous darkness under 35°C. Thermoperiods of different amplitudes with the same mean temperature clearly proved that the higher temperature is responsible for higher rate of diapause development inspite of the relatively low temperature.