| The Asian corn borer, Ostrinia furnacalis (Guenee) (Lepidoptera:Crambidae), is widely distributed from south to north in China and is a major pest of corn, Zea mays L. The Asian corn borers damage corn by boring into stem and fringe. The borers are full-grown by fall, but remain in their host plants over the winter. In this thesis, we investigated geographic variation in diapause and biological characteristics of the Asian corn borer. The results are as follows.1. Geographic variation in the induction and termination of diapause in the Asian corn borerThe photoperiodic response, the critical photoperiod, sensitive stage to photoperiod and diapause termination of the Asian corn borer from six different latitudes:Ledong (LD), Hainan, (18.8°N,109.2°E); Yangshuo (YS), Guangxi, (24.8°N,110.5°E); Nanchang (NC), Jiangxi (28.8°N,115.9°E); Taian (TA), Shandong (36.2°N,117.1°E); Langfang (LF), Hebei (39.5°N,116.7°E); Haerbin (HEB), Heilongjiang (44.9°N,127.2°E) were investigated. The results indicated that the photoperiodic response curves showed a typical long day response in YS, NC, TA, LF and HEB populations at all temperatures tested. The incidence of diapause increased with latitude. The critical photoperiod prolonged with the increase in latitude and was positively correlated with latitude. Nearly all individuals in LD population develop without diapause at 25,28 and 31℃. However, LD population showed a weak photoperiodic response at 22℃. When the diapause-averting photoperiod of L16:D 8 was interrupted by 4 short days at 25℃or when the diapause-inducing photoperiod of L12: D12 was interrupted by 4 long days, there were significant differences in the incidence of diapause among different populations. However, all populations showed that the L3-L4 larvae were the stages most sensitive to the photoperiod. The duration of diapause was significantly different among different populations. The duration of diapause in HEB was longest, followed by TA, LF and NC populations. The duration of diapause was positively correlated with latitude.2. Diapause response of night-interruption in two different geographic populations of the Asian corn borerThe photoperiodic response and effects of night-interruption experiments, in which the scotophases of L9:D15 and L12:D12 were interrupted by 1 h light pulse, on diapause-averting, were investigated at 25 and 28℃in Nanchang (28°41′N,115°53′E) and Haerbin (44°56′N,127°10′E) populations of O. furnacalis. The results showed that the critical daylength in Haerbin population at 25 and 28℃was 1h 40 min and 2 h longer than that in Nanchang population, respectively. At all night-interruption experiments, the incidences of diapause in almost all positions of light pulse in Nanchang population were significantly lower than that in Haerbin population. When the light pulse was used to interrupt L9:D15 and L12:D12, the incidence of diapause was lower in L9:D15 than that in L12:12. Furthermore, the most highly photo-sensitive position occurred in the middle of scotophase at L9:D15, whereas the most highly photo-sensitive position occurred in the early scotophase at 25℃. The effect of the light pulse on diapause-averting at 28℃was greater than that at 25℃. Our results further suggest that effect of night-interruption on diapause-averting may be different even in the same species depending on different geographic populations and the experimental conditions.3. Geographic variation in developmental duration of the Asian corn borerThe developmental duration of egg, larva and pupa of the Asian corn borer from five different latitude (Yangshuo, Guangxi,24.8°N,110.5°E; Nanchang, Jiangxi,28.8°N, 115.9°E; Taian, Shandong,36.2°N,117.1°E; Langfang, Hebei,39.5°N,116.7°E; Haerbin, Heilongjiang,44.9°N,127.2°E) were compared at 20-25℃. And then the relationship between egg duration, larval duration, pupal duration and latitude was analyzed. The results indicated that there were not significant differences in egg durations among the different latitudes at different temperatures and the egg duration was positively correlated with latitude. There were significant differences in larval durations among different latitudes at 22,25 and 28℃, and the larval duration was positively correlated with latitude. However, the larval duration was not significantly different at 20 and 31℃, and there were negative correlations between the larval duration and latitude. There were significant differences in pupal durations among different latitudes except 31℃and there were positive correlations between the pupal duration and latitude. These results further suggest that the geographic variation in developmental duration may be different in different stage and different experimental conditions in the same specie of insects.4. Geographic variation in lower development threshold and sum of effective temperatures of the Asian corn borerThe LDT and SET of egg, larva and pupa of the ACB from five different latitudes: Yangshuo, Guangxi, (24.8°N,110.5°E); Nanchang, Jiangxi (28.8°N,115.9°E); Taian, Shandong (36.2°N,117.1°E); Langfang, Hebei (39.5°N,116.7°E); Haerbin, Heilongjiang (44.9°N,127.2°E) were compared. And then the relationship between LDT/SET and latitude was analyzed. The results indicated:(1) The LDT increased with increasing latitude. form south to north, the LDT is 8.50、9.24、9.18、10.02 and 9.96℃, respectively; while the SET decreased with increasing latitude, form south to north, the SET is 79.27、76.19、77.96、73.37 and 75.32 day-degrees (dd), respectively. (2) The LDT of female larvae increased with increasing latitude and The LDT of male larvae decreased with increasing latitude. Form south to north, the LDT of female larvae is 6.71、9.85、9.81、10.82 and 7.83℃, respectively; and the LDT of male larvae is 11.80、11.90、10.81、12.43 and 9.59℃, respectively, while the SET of female and male larvae increased with increasing latitude. Form south to north, the SET of female larvae is 480.49、440.16、450.82、397.32 and 591.54 dd, respectively, and the SET of male larvae is 370.86、378.73、418.20、346.10 and 532.93 dd, respectively. (3) the LDT of female and male pupae increased with increasing latitude. Form south to north, the LDT of female pupae is 10.95、12.02、11.74、11.97 and 11.62℃, respectively, and the LDT of male larvae is 11.25、11.93、12.01、11.97 and 12.61℃, respectively, while the SET of female and male larvae also increased with increasing latitude. Form south to north, the SET of female larvae is 111.17、107.36、111.23、106.32 and 114.98 dd, respectively, and the SET of male larvae is 108.58、106.84、107.45.108.01 and 109.46 dd, respectively. These results indicated the LDT and SET of the ACB varied from populations, while the variation extent differed by stages.5. Geographic variation in fecundity of the Asian corn borerThe longevity of adult, oviposition period and egg-production of the Asian corn borer from five different latitudes:Ledong, Hainan (18.8°N,109.2°E); Nanchang, Jiangxi (28.8°N,115.9°E); Taian, Shandong (36.2°N,117.1°E); Langfang, Hebei (39.5°N,116.7°E) and Haerbin, Heilongjiang (44.9°N,127.2°E) were compared. The relationship between longevity, oviposition period, egg-production and latitude was analyzed. The results indicated that the longevity of female and male gradually increased with latitude (from 10.20 to 16.40 d for female; from 8.35 to 13.30 d for male). Both oviposition period and egg-production also increased with latitude. From low latitude to high latitude, the oviposition period was 7.45,10.45,11.90,10.62,13.15 d, and the egg-production was 351.55,500.09,522.90,546.76,577.95 eggs, respectively. This result first reveals the geographic variation in reproductive tactics of O. furnacalis.6. Geographic variation in body weight and size of the Asian corn borerThe body weight and body size of the Asian corn borer from four different latitudes: Ledong, Hainan (18.8°N,109.2°E); Yangshuo, Guangxi, (24.8°N,110.5°E); Nanchang, Jiangxi (28.8°N,115.9°E); Langfang, Hebei (39.5°N,116.7°E) were compared. And then the relationship between body weight, body size and latitude was analyzed. The results indicated that egg weight of the Asian corn borer gradually increased with an increase in latitude that followed Bergmann’s law, whereas the pupal weight, body length, hind femur length and fore wing length for both female and male gradually increased with an increase in latitude that followed Converse Bergmann’s law. Fore wing length of the female is significantly longer than that of the male in the four geographic populations and the sexual size dimorphism followed the Rensch’s rule, with the fore wing length of males relatively larger compared to that of females in populations with large body size. These results further suggest that the geographic variation in body weight and size may be different in different stage in the same specie of insects. |
