Abstract
The northernmost Harbin strain (N strain) of the Asian corn borer, Ostrinia furnacalis enters facultative diapause as fully grown larvae in response to short daylengths; whereas the southernmost Ledong strain (S strain) exhibits almost no diapause under the same light conditions. In the present study, we examined the inheritance of diapause induction and termination by crossing the two strains under a range of environmental conditions. The N strain showed a typical long-day response with a critical daylength of approximately15.88 h at 22°C, 15.72 h at 25°C and 15.14 h at 28°C, whereas the S strain showed a weak photoperiodic response at 22°C. The F1 progeny also showed a long-day response at 22, 25 and 28°C. However, the critical daylengths in S ♀ × N ♂ crosses were significantly longer than those in N ♀ × S ♂ crosses, indicating a sex linkage in the inheritance of diapause induction, with the male parent having more influence on the following F1 progeny. The incidence of diapause in S ♀ × N ♂ crosses was the same as in the N strain under short daylengths of 11-13 h, indicating that diapause trait is completely dominant over the non-diapause trait. The critical daylength in backcross to N was significantly longer than it was in backcross to S, showing a grandfather gene effect. Whether the inheritance of diapause fits an additive hypothesis or not was dependent on the rearing photoperiod, and the capacity for diapause was transmitted genetically in the manner of incomplete dominance. The duration of diapause for the reciprocal crosses under different diapause-terminating conditions showed different patterns of inheritance. The results in this study reveal that genetic and genetic-environmental interactions are involved in diapause induction and termination in O. furnacalis.
Highlights
Diapause is an endocrine controlled mechanism by which an organism avoids the effects of a temporarily hostile environment during certain stages of its life history [1]
It is of interest to note that the incidence of diapause (97– 100%) for the S × N crosses was the same as the N strain (98–100%) under the short daylengths of 11–13 h at all temperatures, indicating that diapause is completely dominant over non-diapause
Results from photoperiodic response curves in O. furnacalis (Fig. 1) revealed that the induction of diapause was highly sensitive to photoperiod in the northernmost Harbin strain; most larvae entered diapause under short daylengths of 11–13 h, even at 28°C
Summary
Diapause is an endocrine controlled mechanism by which an organism avoids the effects of a temporarily hostile environment during certain stages of its life history [1]. A latitudinal cline in the incidence of diapause, in which the strains of insect species from temperate regions undergo photoperiodic induction of diapause but the strains inhabiting tropical regions are entirely free of diapause, or only a few individuals enter diapause under conditions of short daylength and low temperature, has been reported in a number of insects, such as the pink bollworm, Pectinophora gossypiella [6,7], the flesh fly, Sarcophaga peregrina [8], the twospotted spider mite, Tetranychus urticae [9,10] and the cotton bollworm, Helicoverpa armigera [11] Such populations usually inhabit rather broad and distinct geographical regions. An introduction of low-diapause genes into a temperate population would radically reduce the incidence of diapause, seriously affecting the overwintering capabilities of the population
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