Inheritance Of Diapause And Comparisons Of Life-history Traits Between The Direct Development And Diapause Individuals Among Different Geographical Populations Of The Asian Corn Borer, Ostrinia Furnacalis

The Asian corn borer, Ostrinia furnacalis(Guenée)(Lepidoptera: Crambidae), is a serious economic pest of maize and is widely distributed in corn producing regions throughout China. This borer enters facultative diapause as fully grown larva in response to short-day conditions during the autumn, so the life history of one year is from 1 to 7 generations from the northernmost Harbin populations to the southernmost Ledong population. As a result of geographical variations in photoperiodic response, the moth provides an excellent material to study the inheritance of diapause and geographical variations of life-history traits. In this dissertation, a new device adapted to observe the termination of larval diapause was produced. The inheritance of diapause in crosses between the northernmost and the southernmost strains were investigated and the differences of life-history traits between the direct developing and diapause developing individuals from six different geographical populations were compared. The results are as follows.1、A new device adapted to observe the termination of larval diapause in the Asian corn borer, Ostrinia furnacalisThe new device is consisted of the plastic pallet, foam board with holes, transparent cylindrical tube and absorbent cotton. The application method is as follows. A foam board is put on a plastic pallet with some water. The diapausing larvae are individually placed in a cylindrical tube and the both ends of the cylindrical tube are plug with absorbent cotton. Then, the cylindrical tubes are inserted to the holes of foam board. Finally, the devices are transferred to inducing-development conditions to observe the termination of diapause. This device finely simulates the external environment of diapause termination in the field and meets the water needs of the diapausing larvae. Using the new devices, we successfully observe the termination of diapause from six geographical populations originated from Huizhou, Yongxiu, Hefei, Taian, Langfang and Shenyang under LD 18:6 at 25 °C and natural conditions. More than 85% diapausing larvae pupated at the two treatments. The experimental method is simple and can also use to observe the course of pupation for overwintering larvae and forecast the date of adult emergence in the field.2、Inheritance of Diapause in Crosses between the Northernmost and the Southernmost Strains of the Asian Corn Borer Ostrinia furnacalisThe northernmost Harbin strain(N strain) of the Asian corn borer, Ostrinia furnacalis from Harbin city(44.9° N, 127.2° E) enters facultative diapause as fully grown larvae in response to short daylengths; whereas the southernmost Ledong strain(S strain)from Ledong county(18.5° N, 108.9° E) 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 for diapause induction 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.3、Comparisons of life history traits between direct developing and diapause developing individuals of the Asian corn borer Ostrinia furnacalis among different geographical populationsThe newly hatched larvae for the six populations(HB, SY, LF, TA, HF and YX populations) of O. furnacalis were reared on an artificial diet at 25 °C under their own critical daylength to produce directly developing and diapause developing individuals. Then, the differences of life-history traits between the direct developing and the diapause developing individuals were compared. The results showed that the larval development time was significantly longer in diapausing individuals than direct development individuals. Significant difference of pupal development time for female between the direct developing and the diapause developing individuals was only found in LF and TA populations, i.e. the pupal development time was significantly longer in the direct developing individuals than the diapause developing individuals; Whereas pupal development time for male showed that the direct developing individuals significantly longer than the diapause developing individuals. The longevity was significantly longer in the direct developing individuals than the diapause developing individuals in all populations. The both pupal and adult weights were significantly greater in the direct developing individuals than the diapause developing individuals in all populations. Except for TA population, the direct developing individuals for females lost less weight compared to the diapause developing individuals. However, the direct developing individuals for males lost more weight compared to the diapause developing individuals. The pupal and adult weights were greater in females than males in both developmental pathways, exhibiting sexual size dimorphism.The dimorphism in adult weight was more pronounced than in pupal weight, because male pupae lost more weight at metamorphosis compared to male pupae. The growth rate in diapause developing individuals was significantly lower than that in the direct developing individuals in all populations. Except for HB population, there were negative relationship between the duration of development and the pupal weight for both developmental pathways. These results reveal that diapause is involved cost.