Abstract:  To understand the thermoperiodic response of the cotton bollworm, Helicoverpa armigera (Hübner), the effects of thermoperiod on larval development and pupal diapause in 4 different geographic populations (Guangzhou population, 23.08°N, 113.14°E; Yongxiu population, 29.04°N, 115.82°E; Tai’an population, 36.15°N, 116.59°E; and Kazuo population, 41.34°N, 120.27°E) were systematically investigated under the photoperiod of L12∶D12. The results showed that at the same photophase temperature there were no significant differences in the larval duration (P＞0.05) between 20T (thermophase, 20℃)∶ 5C (cryophase, 5℃) (12 h photophase temperature∶12h scotophase temperature) (the rest in the same analogy) and 20T∶9C， 22T∶5C and 22T∶9C， 25T∶5C and 25T∶9C， and 28T∶5C and 28T∶9C, respectively, in 4 different populations. However, at the same or near average temperature, the larval duration at  20T∶9C (an average temperature of 14.5℃) was significantly higher than that at 22T∶5C (an average temperature of 13.5℃) (P＜0.05); the larval duration at 20T∶20C (a constant temperature of 20℃) was significantly higher than that at 28T∶9C (an average temperature of 18.5℃) (P＜0.05), suggesting that the larval development is influenced strongly by the photophase temperature. At the same or near average temperature, the diapause rates in 4 different populations at 20T∶9C were higher than those at 22T∶5C, and the diapause rates at 25T∶ 20C (an average temperature of 22.5℃) were higher than those at 28T∶9C (an average temperature of 18.5℃); the diapause rates in 4 different populations at 20T∶20C  were significantly higher than those at 28T∶5C (an average temperature of 16.5℃) (P＜0.05). However, there were significant differences (P＞0.05) at the same photophase temperature between 20T∶5C and 20T∶9C， 22T∶5C and 22T∶9C， 25T∶5C and 25T∶9C， and 28T∶5C and 28T∶9C, respectively, suggesting that the diapause induction is influenced strongly by the photophase temperature. At the same thermoperiod, the larval duration and diapause rate were significantly different among different geographic populations. The larval duration and diapause rate were positively correlated with latitude of habitat, suggesting that sensitivity to temperature is gradually enhanced with a decrease in latitude of habitat.

Key words:  Helicoverpa armigera, geographic population, developmental duration, diapause induction, thermoperiod, photoperiod