Comparisons Of Diapause And Biological Characteristics Among Different Geographic Populations Of The Cotton Bollworm,Helicoverpa Armigera(H(u|¨)bner)(Lepidoptera:Noctuidae)

The cotton bollworm, Helicoverpa armigera (Hubner) is one of the most important agricultural pests in the global and mainly damages cotton, corn and other crops. It widely distributes in different climatic zones of the world, and it is a kind of the multivoltine pests, with a facultative winter pupal diapause. Diapause characteristics are reflected in an important indicator of ecological adaptation of the cotton bollworm, but also are the main factors to determine their geographical distribution. In this thesis, we systematically investigated the differences of diapause and biological characteristics among different geographic populations of the cotton bollworm. The results are as follows.1. Comparisons of diapause-induction and-termination among different geographic populationsThe geographic variations in the induction and termination of diapause were systematically investigated in the cotton bollworm, Helicoverpa armigera from5different geographic populations (Guangzhou population,23.08°N,113.14°E; Yongxiu population,29.04°N,115.82°N; Taian population,36.15°N,116.59°E; Langfang population,39.31°N,116.42°E; Kazuo population,41.34°N,120.27°E) in China. The photoperiodic response cueves indicated that the incidence of diapause and the critical photoperiod for pupal diapause induction increased with increasing geographical latitude at20-28℃. The critical daylength changed by about1.2h with every5°of latitude. Guangzhou population exhibited lower diapause rates (26.53～21.05%) under the short days of12-13h at20℃. Yongxiu population developed without diapause regardless of photoperiods when the temperature exceeds22℃. The duration of diapause was significantly different among different populations, and was positively correlated with latitude. The termination of diapause did not require cold stimulation, and high temperature could enhance the termination of diapause. However, chilling processing allows the relative concentration of adult emergence. The northern populations were lower sensitive to chilling than the sourthern populations. These results further revealed that the sensitivity to temperature is stronger in southern populations than in the northern populations, while the sensitivity to photoperiod is stronger in northern populations than in the southern population.2. Comparisons of photosensitivity of diapause during larval development among different geographic populationsThe geographic variation of photosensitivity was investigated by transferring larvae between long photoperiod (L16:D8) and short photoperiod (L12:D12) under the20℃conditions in3different geographic populations (Yongxiu population, Taian population, Kazuo population). When the photoperiodic background of L12:D12was interrupted by5×L16:D8at different larval stages, the most photosensitive stage occurred in the L4/4to the L5/3stages for Yongxiu population, the L3/5to the L5/1stages for Taian population and the L6stage for Kazuo population. When Taian population and Kazuo populations were exposed to alternating short photoperiod and long photoperiod, respectively, Taian population showed the most photosensitive stage before the fifth instar, Kazuo population showed the most photosensitive stage after the fourth instar. These results revealed that the most photosensitive stage is different in different geographic populations in H. armigera.3. Effects of thermoperiod on larval development and pupal diapause in different geographic populationsThe effects of thermoperiod on larval development and pupal diapause in4different geographic populations (Guangzhou population, Yongxiu population, Taian population and Kazuo population) were systematically investigated under the photoperiod of L12:D12. The results showed that, at the same photophase temperature, there were no significant differences in the larval duration(P>0.05) between20T (thermophase,20℃):5C(cryophase,5℃)(12h photophase temperature:12h scotophase temperature)(the rest in the same analogy) and20T:9C,22T:5C and22T:9C,25T:5C and25T:9C,28T:5C and28T:9C in4different populations. However, at the same or near average temperature, the larval duration at20T:9C (an average temperature of14.5℃) was significantly higher than that at22T:5C (an average temperature of13.5℃)(P<0.05); the larval duration at20T:20C (a constant temperature of20℃) was significantly higher than that at28T:9C (an average temperature of18.5℃)(P<0.05), indicating that the larval development was influenced strongly by the photophase temperature. At the same or near average temperature, the diapause rate in4different populations at20T:9C was higher than that at22T:5C, the diapause rate at25T:20C (an average temperature of22.5℃) was higher than that at28T:9C (an average temperature of18.5℃); diapause rate in4different populations at20T:20C was significantly higher than that at28T:5C (an average temperature of16.5℃)(P<0.05). However, there were significant differences at the same photophase temperature between20T:5C and20T:9C,22T:5C and22T:9C,25T:5C and25T:9C,28T:5C and28T:9C (P>0.05). This indicates the diapause induction is influenced strongly by the photophase temperature. At the same thermoperiod, the larval duration and diapause rate are significantly different among different geographic populations. The larval duration and diapause rate is positively correlated with latitude, suggesting that sensitivity to temperature is gradually enhanced with a decrease in latitude.4. A comparison of night-interruption on diapause-averting among two different geographic populationsSo far, all the photoperiodic responses in insects are highly sensitive to night-interruption, and the long night effect is reversed by a light break. In the present study, the photoperiodic response and effects of night-interruption on diapause-averting, in which the scotophases of L9:D15and L12:D12were interrupted by1h light pulse, were investigated at25℃and22℃in Taian (TA,36.15°N,116.59°E) and Kazuo (KZ,41.34°N,120.27°E) populations of the cotton bollworm Helicoverpa armigera. The photoperiodic response curves showed that the incidences of diapause in the scotophases of11-14h were significantly lower in Taian population than in Kazuo population; the critical night length in Taian population at25℃and22℃was11.7h and11.5h, respectively, and1h20min longer than that in Kazuo population (10.5h and10.3h). At all night-interruption experiments, the incidences of diapause in almost all positions of light pulse in Taian population were significantly lower than that in Kazuo population, however, the diapause response curves was similar in the two populations. Under L9:D15, the incidence of diapause was inhibited most effectively in both Taian population and Kazuo population when the light pulses were placed9-11in the darkness. Under L12:D12, the incidence of diapause was lowest at25℃in both Taian population and Kazuo population when the light pulses were placed3-4h and10h in the darkness; however, Kazuo population only showed a peak of diapaus-averting occurring in3-4h in the darkness at22℃. Our results reveal that southern Taian population is more sensitive to night-interruption than northern Kazuo population, but the most highly photosensitive position is similar.5. Effects of photoperiodic and temperature on the diapause intensity in different geographic populationsThe effects of photoperiod and temperature on diapause intensity of Helicoverpa armigera from4different geographic populations (Guangzhou population, Yongxiu population, Taian population, and Kazuo population) were systematically investigated. The results indicated that photoperiod has a significant influence on diapause intensity in the range from11to14h daylengths. Generally, longer daylength can induce stronger diapause intensity. The diapause intensity was influenced strongly by the photophase temperature of thermoperiod. The diapause intensity induced at thermoperiod temperature was stronger than that at constant temperature in Guangzhuo population. On the contrary, the diapause intensity induced at thermoperiod temperature was not stronger than that at constant temperature in northern Kazuo and Taian population. However, there was the same diapause intensity in Yongxiu population regardless of thermoperiod or constant temperature. Higher constant temperature induced a stronger diapause, the more northern latitudes, and this trend more evident. The diapause intensity was negatively correlated with latitude under the same photophase temperature (20-25℃).6. Comparisons of eclosion rhythm and sex ratio in overwintering pupae among different geographic populationsThe eclosion rhythm and sex ratio of overwintering pupae from4different geographic populations (Guangzhou population, Yongxiu population, Taian population and Kazuo population) were systematically investigated. The results indicated that the eclosion behavior of the southern populations (subtropical geotypes) mainly occurred at16:00～23:00, about accounted for94～97%, but that of the northern populations (temperate geotypes) occurred at17:00～6:00, all night, and about accounted for98%. The eclosion peak times of the northern populations were one hour later than that of the southern populations. Under same conditions, the time of eclosion in the northern populations was suspended for9～13days in contrast to the time in the southern populations. In addition, there was distinctly geographic variation in the sex ratio of adults emerged from overwintering pupae, the sex ratio of the southern population females and males was1:1, but that of the northern population was1:1.8. There was a phenomenon of protogyny in overwinter generation adults; the time of female eclosion were3～7days earlier than that of male eclosion.7. Comparisons of the developmental duration among different geographic populationsThe developmental durations of larvae, non-diapause pupae and diapause pupae from4different geographic populations (Guangzhou population, Yongxiu population, Taian population and Kazuo population) were systematically investigated under20,22,25and28℃. The results showed that the developmental duration of larvae increased with increasing geographical latitude, Larval duration was significantly negatively correlated with latitude at25℃, but at the other temperature, the larval duration was not significantly negatively correlated with latitude, and the development duration of female and male larvae is similar without showing significant differences. At20℃, there was significant negative correlation between pupal duration and latitude, but at the other temperature, there was positive correlation, and male pupal duration was slightly longer than female pupal duration, but the difference was not significant. These results further suggest that the geographic variation in developmental duration may be different in different stage and different experiment conditions in the same specie of insects.8. Comparisons of lower development threshold (LDT) and sum of effective temperatures (SET) among different geographic populationsThe LDT and SET of larvae, non-diapause pupae and diapause pupae from4different geographic populations (Guangzhou population, Yongxiu population, Taian population and Kazuo population) were systematically investigated under20,22,25and28℃. The results showed that the LDT of larvae, non-diapause pupae and diapause pupae were10.18-12.19,10.60～13.50and15.56～17.96℃, respectively, their SET were254.91～300.89,126.21～204.43and181.03～363.39day-degrees, respectively. The LDT of diapause pupae was3.39～5.50℃more than that of non-diapause pupae, and its SET was35.56～165.89day-degrees more than that non-diapause pupae. The LDT of larvae, non-diapause pupae and diapause pupae decreased with increasing geographical latitude; whereas the SET increased with increasing geographical latitude.