| Alternanthera philoxeroides is a serious perennial invasive weed which was introduced into China in the 1930 s. Due to its strong productive abilities and ecological adaptability, it has extended to most areas of China and caused extremely serious losses. Agasicles hygrophila, an effective specialized natural enemy insect of A. philoxeroides, has been introduced to the United States, Australia, Thailand, New Zealand and other countries for controlling alligator weed. In the subtropical area of China, temperature is the main factor affecting biological control of alligator weed. Thermal adaptability of A. hygrophila is poor, and in some areas its population density declines sharply from early August to late September when the temperature is extreme high, which limits the control efficiency of A. philoxeroides in summer. However, the population density keeps high in Hainan at the same time, indicating the evolution of thermal adaptability among different populations could be different.In order to reveal the differences of thermal adaptability and regulatory mechanism between geographical populations of A. hygrophila, we constructed the age-stage, two-sex life tables of tropical Hainan population and subtropical Changsha population under different high temperatures at 12:00~16:00 for two generations, with the treatment at 25 ± 1℃ as control. The main results are as follows:1. The continuous generations’ age-stage, two-sex life tables of A. hygrophila Changsha population under different temperatures were constructed. The results showed that the developmental time of egg, larva, and entire immature stage of both generations of Changsha population were prolonged significantly with temperature increasing between 30~36℃, while the longevity was significant shorter at more than 33℃, oviposition period and number of eggs laid per female decreased significantly with increased temperature. The intrinsic rate of increase(r) and finite rate of increase(λ) of F1 were decreased significantly by increased temperature between 30~36℃, and mean generation time(T) under heat treatments was shorter than 25℃, fecundity at 33℃ and 36℃ were less than 25℃ and 30℃; As similar with F1, the intrinsic rate of increase, finite rate of increase and fecundity of F2 decreased with elevated temperature between 30~36℃.2. We constructed the continuous generations’ age-stage, two-sex life tables of A. hygrophila Hainan population. The developmental time of larva and entire immature stage of F1 was significantly prolonged when the temperature rose between 30~36℃, longevity and number of eggs laid per female at 33℃ and 36℃were less than 25℃, intrinsic rate of increase, finite rate of increase and fecundity at 33℃and 36℃were less than those at 25℃ and 30℃; The developmental time of egg, larva, pupa and entire immature stage of F2 were prolonged significantly with increasing temperature between 30~36℃, however there was no significant differences in oviposition period and number of eggs laid per female, as well as longevity of female among 4 treatments. With the temperature rising, intrinsic rate of increase and finite rate of increase of F2 were significantly decreased, meanwhile mean generation time was prolonged, and fecundity at 33℃ and 36℃ was less than those at 25℃ and 30℃.3. At first the differences of thermal adaptability between two generations of A. hygrophila Changsha population were compared. Intrinsic rate of increase and finite rate of increase in F2 were decreased and mean generation time was prolonged when insects exposed at 33℃ and 36℃. Fecundity of Changsha F2 population was higher than F1 at 33℃, while less than F1 at 36℃; Intrinsic rate of increase and finite rate of increase of Hainan F2 were higher than F1 at 33℃, while there was no significant difference in fecundity. Compared with Hainan F1, intrinsic rate of increase, finite rate of increase and fecundity of Hainan F2 significantly decreased at 36℃.4. We compared the differences of thermal adaptability between two populations of A. hygrophila. Intrinsic rate of increase and finite rate of increase of Changsha population F1 at 30℃ and 33℃ were higher than Hainan F1, while intrinsic rate of increase and fecundity of Hainan F1 was higher than Changsha F1 at 36℃; Intrinsic rate of increase and finite rate of increase of Hainan F2 were higher than Changsha F2 at 33℃, moreover, all parameters of life table were higher than Changsha F2 at 36℃.In conclusion, thermal stress could reduce the population fitness of A. hygrophila, resulting in decreased longevity and fecundity. Heat tolerance of tropical Hainan population was higher than subtropical Changsha population, indicating the differences of thermal adaptability among geographical populations of A. hygrophila. High temperature negatively affected continuation of A. hygrophila, and the effect on Changsha population was more serious than Hainan population. The study has important theoretical and practical significance for the biological control of A. philoxeroides in summer, and laid foundation for heat acclimatization and releasing natural enemy across latitude. |
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