Comparison Of Life History Traits And High Temperature Tolerance Of Trichogramma Strains Collected From Paddy Fields In The Mekong Subregion

Trichogramma is one of the most widely used egg parasitoids in biological control. There are lots of Trichogramma species or strains around the worldwide. The difference of biological and ecological characteristics of Trichogramma species or strains may directly affect the biological control effects. Therefore, it is necessary to compare their biological and ecological characteristics of Trichogramma species or strains before their release. We collected Trichogramma species or strains from paddy fields in the Mekong Subregion, and reared them on the eggs of Sitotroga cerealella in the laboratory. The comparsions of life history characteristics and high temperature tolerance of Trichogramma species or strains were determined. The main results are as follows:1. The life history characteristics of Trichogramma species or strainsThere were significant differences in life history characteristics of Trichogramma species or strains at25℃. The fecundities of Trichogramma chilonis Myanmar and the Wulipai strains and T. ostriniae Hebianzhai strain were59.9,53.5and54.4, respectively, which were significantly higher than the others. The longevity of T. chilonis Cuijia strains was8.2day, which was significantly longer than T. chilonis Wulipai and Taiwang strains and T. japonicum Guangdong strain. Immature development duration of T. chilonis Taiwang strain was10.0day, which was significantly shorter than the other strains, while T. ostriniae Mangzhai strain was13.3day, which was significantly longer than the others. In contrast, the emergence and sex ration of T. japonicum Guangdong strains were the highest among all other strains studied. The emergences of all strains studied were greater than80%except T. ostriniae Mangzhai strain, which was70.5%.The population life tables of Trichogramma species or strains reared on eggs of Sitotroga cerealella were formated under the laboratory conditions. The results showed that the intrinsic rate of increase (rm) of T. chilonis Myanmar and Wulipai strains and T. ostriniae Hebianzhai strain were0.33,0.34,0.29, respectively, all of which were significantly higher than the other strains.2. Effect of temperature on development and fecundity of female Trichogramma species or strains Under different temperature conditions, the growth and development, female longevity and fecundity of Trichogramma species or strains differred greatly. The upper survival temperature of T. chilonis strains was37℃, whereas T. ostriniae was about35℃. The development duration of immature was shortened as temperature increased in the range of25℃-34℃, while there was no significant difference between34℃and37℃. The longevities of female Trichogramma species or strains reduced with temperature. The longevities of T. chilonis strains were significantly longer than those of T. ostriniae and T. japonicum in the range of25℃and34℃. At37℃, the females Trichogramma species or strains could only survive for1day. The fecundity of T. chilonis strains were significantly higher than that of T. ostriniae strains under the same temperature conditions. The fecundities of T. chilonis strains were highest at28℃, while T. ostriniae strains at25℃. The fecundity, regardless of Trichogramma species or strains gradually reduced in the range of31and37℃, and the reducing trends of T. ostriniae strains were signicficantly different from those of T. chilonis strains. The fecundity of T. chilonis Wulipai strain at34℃did not differ from that at31℃.3. Stage sensitive of Trichogramma species or strains to high temperature exposureThe sex ration of different developmental stages of Trichogramma species or strains exposed to37℃for4,8and12h, were not significantly different from that in the control group. Similarly, the emergence rations did not differ among different developmental stages, the egg and larvae stages of Trichogramma species or strains were more sensitive than pupa stage. The results showed that Trichogramma species or strains were tolerant to37℃in a short period of high temperature exposure. The T. chilonis and T. ostriniae Mangzhai strains were more sensitive than other strains. Egg and larvae stages of Trichogramma species or strains were more sensitive to high temperature as the duration of high temperature exposure increased. The emergence of the parasitized eggs exposed to high ermperature for12h, was significantly lower than those of4h and8h.