Physiological Ecology Of The Rice Leafroller Cnaphalocrocis Medinalis In Reproduction And Flight

Cnaphalocrocis medinalis (Guenee)(Lepidoptera: yralidae) is one of the most important migratory rice pests; it may cause huge losses on rice production. The factors determining flight and reproduction are important for predicting the migratory peaks. This paper explored the anatomic criteria to determine the adults reproductive diapause; compared the impact of host on fecundity and flight capability; studied the effects of flight on reproductive and longevity of the adults; and assessed the influence of ambient temperature, age and reproductive status on adults wing beat frequency. Results are summarized as below:(1) Adult ovaries dissection at different temperature and humidity showed that lower temperature could significantly inhibit the growth of the ovaries, and the length of the ovary and the visible eggs at20℃were significantly shorter than the26℃and32℃after16h of emergence; the length of ovary reached to9mm at26℃and32℃after24h, nevertheless, the length at20℃was less than7mm. Twenty four hrs after eclosion, the ovary length was shorter than7mm at low humidity (50%) and longer than7mm at70%and90%humidity. We found huge difference of free-flight flight duration among different individuals (ranging from2s to900s), and a significant correlation between the female’ovarian development stage and free-flight duration (r=-0.6713, p=0.0002); females with2or3stage ovary were more willing to fly than the moths with other stage of ovary.(2) Corn seedling breeding method is proved to be one of the most reliable methods to provide insects for research. The influence of host plant on adults reproduction and flight physiology still remains unknown. We compared the fecundity and flight capacity of moths fed on rice leaf and corn seedling, and drew a conclusion that there was no significant difference of the pre-oviposition period, oviposition phase and lifetime fecundity (t=1.1457, p=0.2678:t=1.2946, p=0.2180:t=1.6405, p=0.1268, respectively). However, the hatching rate displayed a significant difference (t=2.3017, p =0.0401), and eggs coming from rice treatment hatched with higher rate than rice treatment. The longevity significantly decreased after the female ovipositing in corn treatment, but this situation did not exist in rice treatment. There is no significant difference of the adults flight capacity between the two populations, except that the1-and2-day old adults reared by rice leaf exhibited stronger flight potential than adults reared by corn seeding did at the corresponding age.(3) Our results revealed the pre-oviposition period of the moth was significantly shorten when the female moths flied at the age of1and2day old, while the flight of the3th age had no influence on female pre-oviposition period. The lifetime fecundity of the female reduced gradually as the extension of the flight age, but no significant difference of total eggs was detected compared to the control. On the other way we found that the flight prolonged the adults longevity, the flight of the third age significant extended the moths’lifetime.(4) Wing beat frequency is one of the most important parameters in insects’flight, we studied the ambient temperature, age and reproductive status on WBF of the rice leaf roller moths. The adults longevity showed significant difference among the three temperatures (16℃,26℃,32℃), the adults lived as long as30.6d at16℃, and was significant longer than the treatments of26℃(10.7d) and32℃(8.8d). The WBF showed no significant difference when the moths were1day old. Nevertheless, temperature had a great effect on the wing beat frequency after the moths were2day old. The moths’WBF under32℃decreased and significantly lower than the treatments of26℃and16℃, the changing tendency of moths’WBF under26℃was rising first and decreasing after the adults reaching to5day old, the WBF slowly went up under16℃. Meanwhile, we investigated the correlation between WBF and tethered flight duration (TFD) both using the laboratory-rearing and field-collected moths, and had found a significant correlation between WBF and TFD in both two source of population(Υ=0.844, p<0.001; Υ=0.58, p=0.005), thus we believe that WBF can reflect the flight capacity of Cnaphalocrocis medinalis in a way, and may be a parameter to access the flight capacity. Conclusion: when the ovarian length is short than7mm at the time of24h after eclosion can be used as a anatomic criteria to determine the occurrence of the adults reproductive diapause; the ovarian development stages and its free-flight duration have a trade off relationship, that is the lower ovarian development stage of the adults display longer free-flight duration, vice-versa; there is no significant difference of adults reproduction and flight capacity between the two populations reared by rice and corn seeding; flight stared at young ages promotes the ovarian development and urges the female to spawn; wingbeat frequency is positive correlated with tethered flight duration, and it can be one of the parameters to evaluate the flight capacity of the adults.