| The Asia corn borer, Ostrinia furnacalis(Guenée)(Lepidoptera, Crambidae), a serious pest in corn, is widely distributed in China and enters diapause as fully-developed larvae in response to short-day conditions. Thus, the moth is an ideal model organism to test inheritance of photoperiodic control of larval diapause and its geographical variation of life history traits. In this paper, we examined the inheritance of larval diapause and the life-history traits related to temperature and geographical latitude. The results are as follows. 1. Inheritance of photoperiodic control of larval diapause in O. furnacalisThe O. furnacalis shows a distinct geographical variation in photoperiodic control of diapause. The subtropical strain from Hefei city(HF) enters diapause in response to short daylengths, whereas the tropical strain from Ledong county(LD) exhibits almost no diapause under the same conditions. The two strains were used in crosses to study the inheritance of diapause. The HF strain showed a typical long-day response with a critical daylength of approximately14.97 h at 22 °C, 14.60 h at 25 and 13.68 h at 28 °C. The LD strain showed weak photoperiodic responses at 22 and 25 °C; and the F1 progeny also showed a long-day response with significantly shorter critical daylength compared to the HF strain. However, the LD × HF(F x M) crosses had significantly longer critical daylengths than HF × LD crosses, indicating a sex linkage in the inheritance of diapause induction, with the male parent having more influence on the F1 progeny. The critical daylength in a backcross to HF was significantly longer than a backcross to LD. Whether the inheritance of diapause fits an additive hypothesis or not depended on the rearing photoperiod, and that the capacity for diapause was transmitted genetically in the manner of incomplete dominance. Unlike diapause induction, the duration of diapause for reciprocal crosses was equally influenced by each parent, suggesting that diapause incidence and maintenance are controlled by separate systems in O. furnacalis. 2. Life-history traits of the Asian corn borer, O. furnacalis in relation to temperature and geographical latitudeLife-history traits of four geographical populations(tropical LD population,subtropical GZ and YS populations and temperate LF population) of the Asian corn borer, O. furnacalis in relation to temperature and geographical latitude were investigated at a wide range of temperatures. The larval time, pupal time, larval + pupal time of both females and males for all populations were significantly decreased with increasing rearing temperature and growth rate in all populations was positively correlated with temperature. Female larvae required more days to develop than males at all temperatures, whereas male pupae required more days to develop than females at all temperatures. Except at 26°C for the tropical LD population and at 32 °C for the subtropical GZ population, the total development times(from hatching to adults) in females were longer than in males at all temperatures. Pupal weight was significantly influence by temperature, population and sex, showing a result of significant temperature × population × sex interaction, but the influence of temperature on male pupal weight was some different from female pupal weight. Intrestingly, the relationship between body size and rearing temperature in O. furnacalis did not follow the temperature–size rule; all populations exhibited the highest pupal and adult weights at high temperatures or intermediate temperatures. Across all populations at each temperature, female pupae were significantly bigger than males, showing a female biased sexual size dimorphism. Contrary to Rensch’s rule, the sexual size dimorphism for all population was increased with rising temperature. Like pupal weight, there were also significant impacts of temperature, population and sex on adult weight. Male pupae lose significantly more weight at metamorphosis compared to females. The proportionate weight losses of different populations were significantly different. Adult longevity for both female and male in all populations was significantly decreased with increasing temperature. Between sexes, all populations exhibit a rather female-biased adult longevity at all temperatures, average longevity was significantly longer in female than male.Total development time did not show a latitudinal gradient, the subtropical YX population had the longest developmental times at 20, 22, 24, 26 28 and 30 °C but not at 32°C(Fig. 2, Table 1 for temperature × population effect). Total development time was shortest in the temperate LF population at 20 and 22 °C. Growth rate did not show a latitudinal gradient. The temperate LF population had the highest growth rate at 20 and 24 °C; whereas at 26, 28 and 30 °C, the highest growth rate was found in the subtropical GZ population. There were significant differences in pupal weight among different populations(Table 1). The GZ population had the highest female pupal weight at 20, 22, 24, 26, 28 and 30 °C, whereas The LF population had the lowest female pupal weight at 24, 26, 28, 30 and 32 °C. The subtropical GZ population exhibited the largest degree of dimorphism while the temperate LF exhibited the smallest. Adult longevity was significant different among populations at each temperature. The significant temperature × population interaction indicates that the differences in longevity among populations varied when temperature changed.All the results concerning life history traits in this study demonstrate that the pattern of life history varies with temperature and latitude. Therefore, our results emphasize the importance of performing a life history experiment with a wide range of populations under a range of environmental conditions. |
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