Inheritance of photoperiodic control of pupal diapause in the cotton bollworm, Helicoverpa armigera (Hübner)

Abstract

Pupae of the cotton bollworm, Helicoverpa armigera display a diapause in response to the exposure of their larvae to short photoperiods and relatively low temperatures. Due to geographic variation in photoperiodic response, moths from a northern population, Langfang (39°32'N, 116°41'E), enter diapause in response to short daylengths (D strain) while moths from a southern population, Ledong (18°28'N, 108°53'E), exhibit no diapause under the same conditions (N strain). In the present study, crosses between the two strains are utilized to evaluate the inheritance of diapause under different photoperiods at temperatures 20, 22 and 25°C. The moths in both reciprocal crosses and backcrosses to D strain showed a clear long-day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. The incidences of diapause for all F(1) hybrids were intermediate between those of their parents. However, the incidences of diapause at 20°C in F(1) (N×D) strain were significantly higher than those in F(1) (D×N) strain, indicating that the male parent plays a more important role in the determination of diapause. The N strain also showed a short-day photoperiodic response at the lower temperature of 20°C, indicating that the N strain still has the capability to enter a photoperiodically induced diapause, depending on the rearing temperature. Results from all crosses under photoperiods LD 12:12 or LD 13:11 at 22°C showed that inheritance of diapause in H. armigera did not fit an additive hypothesis and that the capacity for diapause was transmitted genetically in the manner of incomplete dominance with non-diapause characteristic partially dominant over the diapausing. Diapause duration in hybrid pupae was also influenced by their inheritance from both parents. Diapause duration in hybrid pupae was intermediate between those of their parents. These results reveal that both diapause induction and duration are under the control of polygene.