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Determination Of Environmental And Physiological Factors Affect The Diapause Induction And Termination In Loxostege Sticticalis L.

Posted on:2010-06-06Degree:MasterType:Thesis
Country:ChinaCandidate:S H HuangFull Text:PDF
GTID:2143360275476269Subject:Agricultural Entomology and Pest Control
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The beet webworm Loxostege sticticalis L. is the important pest of agriculture and pasturage in North, Northeast and Northwest China. It had broken out for three periodicities since the founding of New China and caused huge economic loss to agriculture and pasturage. One of the most important reasons for this pest infesting is not only its long distance migration but the winter diapause characteristic besides the adaption of ecological condition and climate changing in China in recent years. Because of the long distance migration and winter diapauses in this pest, it's difficult to understand the characteristics of the pest source, especially the regularity of diapause overwintering and influence factors on diapauses were not studied systematically. Accordingly, the annually pest overwintering area and source which have a great influence on population infection in next year were unclear. This paper studied on effects of photoperiod and temperature on diapause induction and termination of Loxostege sticticalis and developmental biology variation after diapause and variation of JH titer during diapause period. We hope to reveal the influence of diapause on population dynamic and support some scientific theoretic evidences for population prediction and forecast for this pest.Photoperiod and temperature have a great influence on the diapause induction in the beet webworm Loxostege sticticalis. The interactive effects of temperature (18, 22, 26and 30℃) and photoperiod (L8:D16, L10:D14, L12:D12, L148:D8 and L16:D8) on diapause induction in this moth were investigated by artificial induction method in the laboratory. The photoperiod played the key role in the mature larvae diapause induction, followed by temperature and their interaction. Low temperature was favorable for diapause. Photoperiod response in L. sticticalis showed that it is a typical long-day species with a critical day length of 13.97, 14.48, 13.92 and 12.88 h at 18, 22, 26and 30℃respectively. The short day length of 12 h resulted in the highest diapause rate at all the experimental temperature. The larvae of 11 to 17 days after hatching (about in the 5th instar) were most sensitive to the photoperiod, suggesting that the 5th instar is the most sensitive stage of diapause induction. However, the short daylight received by the 4th instar larvae was also important for their diapause rate increase, diapause rate can be increased from 40.0% to 90.0%.Mature larvae diapause in L. sticticalis can be terminated in suitable temperature without low temperature or long-day stimulation before pupation. However, Lower temperature stimulation at 5℃or 0℃for suitable time can accelerate mature larvae diapause termination. Prophase of larvae pupation was 36 d without lower temperature stimulation compare to that of about 9 d with low temperature stimulation at 5℃or 0℃for 10~60 d. However, the larvae death rate increased significantly after lower temperature stimulation for long time. 5℃or 0℃stimulation for 20~30 d were the best conditions for the mature larvae diapause termination at which prophase of larvae pupation was about 8 d and death rate was lower than 4%.The developmental threshold temperature of prophase of pupation and pupal stage in L. sticticalis after larvae diapause termination were 9.36℃and 10.91℃respectively, and the effective accumulated temperature were 124.68 day-degrees and 197.29 day-degrees respectively in lab condition. Preoviposition period and oviposition period of the female emerge from the diapause larvae were significantly longer than that from non-diapause larvae. Furthermore, the average fecundity per female was significantly lower than that emerge from the non-diapause larvae with the exception of the average life-span of adults prolonged significantly. It presumably suggested that the diapause procedure in Loxostege sticticalis should pay out adult reproduction cost.JH have a great influence on the larvae diapause induction in Loxostege sticticalis. During the initial stage of the 5th instar, JH titer in hemolymph decreased rapidly. However, it then keep the higher titer in the later 5th instar (JH I titer in hemolymph up to 140ng/mL) which could induce the diapause state. The results of JH I titer in hemolymph of diapause prepupae showed it always keep the higher level (up to 100 ng/mL) during the diapauses stages, while decrease significantly from the 5th d before pupation.According to the results of influences of photoperiod and temperature on diapause induction and termination and developmental biology variation after diapause termination in Loxostege sticticalis, also combined with global warming, we clarified the reason that the overwintering area changed from the conventional overwintering area such as north of Shanxi, north of Hebei and Midwest of Inner mongolia to subordinational overwintering area such as east of Inner mongolia, west of Heilongjiang and west of Jilin. Simultaneously, we explained the reason of the diapause rate decreasing for the first generation larvae in main occurrence region of China in recent years. Results obtained from this study would establish the bases for illustrate the changing of overwintering pest source, their overwintering region variation and occurrence regularity, Consequently, It would improve and enhance the population dynamics prediction and forecast level for this pest.The major innovations of this study were as follows:Based on some published results which were related to Loxostege sticticalis diapause, this paper systematically analyzed the influences of photoperiod and temperature on their diapause induction, and first opened out the sensitive development stage and sensitive larval instar of the diapause induction, identified the interaction effects of the photoperiod and temperature on the diapause induction. All these results combined the global climate change indicated that diapause have great influences on the overwintering area distribution, overwintering generation and ratio. Thus it supported a new experimental evidence for improving the forecast and control level of Loxostege sticticalis;Systematically illustrated the effects of photoperiod and temperature on the diapause termination in Loxostege sticticalis, and first clarified that their diapause could be terminated without lower temperature and long daylight stimulation, and evaluated the role of lower temperature on the diapause termination scientificaly;Firstly clarified the variation of pupae development and adult reproduction after Loxostege sticticalis diapause termination, and opened out diapause should pay out some reproduction cost with decrease the adults fecundity. However, moths from the diapause larvae have obvious migration tendency with longer pre-oviposition and longevity. Thus it can explain the essence reason why most of hibernation generation mothes usually migrate into other damaging areas.Firstly explored the role of JH on the diapause of Loxostege sticticalis, clarified the JH titers variation in hemolymph during the diapause state and established the base for lucubrate the diapause hormone regulation.
Keywords/Search Tags:Loxostege sticticalis, diapause, photoperiod, temperature, induction, termination, reproduction cost, juvenile hormone titer
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