| Rice leaf folder (RLF) Cnaphalocrocis medinalis (Giienee) is an important pest in rice, and it usually occurs in the hottest season of a year. There have been some studies on effects of temperature on the occurrence and development of RLF population, but the biological response and adaptation strategy of RLF population to heat shock are still unclear. Thus, based on the rearing method of RLF in laboratory established in this study, the biological traits of RLF were measured under different constant temperatures from 21 to 36℃, and the biological response of pupae and adults to 36-41℃ heat shock for five hours per day was examined. And the possible strategy of RLF to cope with high temperature was also studied. The main results were listed as following:(1) The rearing method of RLF using maize seedlings was established, and the RLFs were reared for three years about 42 generations in laboratory using this method. The survival rate of larvae reared using maize seedlings was 52.60±4.91%. The fecundity of adults was 214.5±26.9 eggs per female, and the eggs hatchability was 78.17±1.11%. The biological traits of RLF reared on maize seedlings and rice were not significantly different. The eggs could be maintained 20 days at the 15℃ when they were acclimated by the stepwise decline of temperature from 25 to 15℃, and the hatchability was not significantly decreased.(2) The biological characteristics of RLF reared on maize seedlings and rice under constant temperature 21-36℃ were checked. The results showed that the RLF reared on rice was a relative higher resistant to high temperature than the RLF reared on maize seedlings. The development duration of RLF reared on maize seedlings under 24-27℃ was longer than that on rice. The development of larvae reared on maize seedlings was significantly inhibited by 30℃, and no larvae developed into adults at 33℃.2However, the development of larvae reared on rice was not affected by 33℃. The survival rate of RLF reared on rice was not significantly different among 27,30 and 33℃, but the mortality became high at 36℃ and few larvae could grow into adults. When the RLF reared on maize seedlings, the survival rate at 33℃ was significantly lower than at 21-30℃癈, and no larvae could develop into the second instar at 36℃. The fecundity of RLF reared on rice and maize seedlings at 24℃ and 27℃ was the highest. At 30℃ and 33℃, the adults reared on rice could lay a few eggs, but the adults reared on maize seedling could not. The eggs hatchability of RLF reared on rice and maize seedlings was the highest at 27℃, and no significant differences between maize seedlings and rice were found. At 33℃ and 36℃, eggs produced by the adults reared on maize seedlings could not hatch, but a few eggs could when their parents reared on rice.(3) The heat shock at 40℃ for five hours per day lasted one to three days significantly prolonged the pupal duration, and decreased the eclosion rate. Three days of heat shock significantly reduced the copulation frequency; and one to three days of heat shock significantly declined the eggs hatchability. When the male pupa exposed to 40℃ for six hours per day and lasted one to two days, the pupal duration was prolonged, and the eclosion rate of pupa was declined, and no pupa could emerge under three days of heat shock. Heat shock for one to two days in pupae stage significantly reduced the copulation frequency, fecundity and eggs hatchability.Heat shock at 40℃ for five hours and lasted two and three days in the pupae stage significantly reduced the number of total sperm and long sperm bundles in testis of male. Heat shock at 40℃ for one and two days, six hours per day in the pupae stage, significantly decreased the number of total sperm and long sperm bundles, and the number of short sperm bundles increased.(4) Heat shock at 36℃ for eight to fourteen hours per day and lasted one to four days, could significantly shorten the adult longevity and oviposition period, inhibit the development of female ovary, and reduce the copulation frequency, fecundity and eggs hatchability. Heat shock at 39-40℃ for five hours and lasted one to three days significantly shortened the adult longevity, and declined the female copulation frequency and eggs hatchability.The male adults of RLF were more sensitive to high temperature than females. After heat shock, the mortality of males was significantly higher than the females. When the male adults shocked at 40℃ or 41℃ paired with unshocked female, the fecundity and eggs hatchability was reduced, but the fecundity of females shocked and unshocked mated with unshocked male adults was not significantly different.40℃ heat shock significantly affected the mating success of RLF, and some female and male adults could not detach after copulation. Heat shock prolonged mating period when both females and males were shocked, and the females did not obtain spermatophore. Newly-born male adults were heat shock at 40℃ for three days, five hours per day, the total number of sperm was not affected, but the number of mature sperm bundles (length≥400μm) was significantly reduced. Before mating, the number of sperm bundles in testis, vesicula seminalis, and ejaculation duct between shocked and unshocked males were not significantly different, but after mating, the numbers of sperm bundles in ejaculation duct and total sperm bundles in these three parts were significantly higher in shocked males than that in unshocked males, while sperm bundles in testis and vesicula seminalis still had no significant difference. Heat shocked males could not ejaculate sperms into females during the mating behaviour.(5) The coexisting mode of female and male adults during the heat shock was disadvantage for RLF to deal with heat shock. When adults exposed to 39℃ for three days (five hours per day), the longevity, ovary development, copulation frequency, fecundity and egg hatchability were significantly lower in the females shocked together with males than the females shocked separately from males. The distance from a male to its nearest female neighbour abruptly increased when the ambient temperature increased to the threshold of 39℃, and the number of adults with the nearest opposite sex neighbor reduced as the temperature increased.The age when female and male adults mating, was significantly affected the fecundity and eggs hatchability. The fecundity of adults paired when they emerged newly was highest. The fecundity was not significantly different among one- to three-day-old females paired with new emerged males, and there was no significant difference among one- to six-day-old males paired with newly emerged females. When RLF adults were stressed by high temperature, the mating behaviour delayed one to two days would not affect the reproduction. |
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