Intra Egg Competition Of Trichogramma Dominant Parasitic Asian Corn Borer (Ostrinia Furnacalis) Based On Microsatellite Markers

Asian corn borer Ostrinia furnacalis is one of the most serious and harmful pests of maize especially in the northeast of China which are the main corn producing areas in China.According to the actual release and recovery of Trichogramma species in the field,most of the eggs hatched by the field parasitic corn borer are Trichogramma ostriniae,while the recovery rate of Trichogramma dendrolimi is low.This phenomenon has led to doubts about the control effect of Trichogramma dendrolimi on Asian corn borer.Published literature showed that intraspecific and interspecific competition occurs among Trichogramma species which may affect the correct evaluation of dominant attacking species during biological control program.The relevant published studies are not comprehensive and due to the small size of host and Trichogramma species the mechanism of competition is not clearly evaluated.Therefore,there are few studies on the mechanism of interspecific competition of Trichogramma.In our study,the parasitic wasps of T.ostriniae were collected from Jilin Province and Heilongjiang Province.After morphological and molecular identification,the dominant species of Trichogramma parasitoids on O.furnacalis in Northeast China were identified.Based on microsatellite molecular marker technology,the DNA of adult wasps of T.dendrolimi,T.ostriniae and eggs of O.furnacalis were used as templates.Microsatellite primers were screened out for two species of Trichogramma.The competition of two species of Trichogramma in O.furnacalis was described in detail by detecting the eggs at different developmental stages after parasitization.Combining the results of two species of Trichogramma parasitizing eggs of Asian corn borer,the control effect of Trichogramma dendrolimi was verified from two aspects,and the field control effect of Trichogramma dendrolimi was correctly reviewed.The main results are as follows.After collection and identification of parasitized eggs in Jilin Province and Heilongjiang Province,it was found that the parasitized rates of O.furnacalis eggs from high to low were: T.ostriniae,T.dendrolimi,T.leucaniae and T.chilonis in Jilin Province;T.ostriniae,T.dendrolimi and T.leucaniae in Heilongjiang Province.The results showed that the species with the best parasitic effect on the eggs of O.furnacalis were T.ostriniae and T.dendrolimi,and their control effect was much higher than other species of Trichogramma.Two pairs of microsatellite primers were screened out from 10 pairs of microsatellite primers designed for identification of T.dendrolimi and T.ostriniae.One pair of microsatellite primer were used for identification of Trichogramma species in the same parasitized egg.All eggs that amplified specific bands of T.ostriniae or T.dendrolimi were parasitized separately,meanwhile the eggs that amplified mixed bands of two Trichogramma species were co-parasitized.The results showed that there were co-parasitized eggs in all the tested eggs after 12 hours of mixed parasitization by T.ostriniae and T.dendrolimi,indicating that the early species of Trichogramma could be identified by SSR microsatellite molecular marker technology.Two Trichogramma species parasitized eggs of O.furnacalis at different developmental times(0 ~ 96 h)were detected by microsatellite detection.The specific bands of two species of Trichogramma can be amplified at the same time from 0 to 48 hours after parasitization.However,only specific bands of T.ostriniae could be amplified which suggesting that there was indeed interspecific competition between the two Trichogramma species after 72 hours of development in the same egg of O.furnacalis and T.dendrolimi may be replaced by T.ostriniae.This result is basically consistent with the results of biological investigation,and according to the development of Trichogramma in the eggs of O.furnacalis,it is likely that competitive interaction occurs when Trichogramma develops to larval stage.To sum up,Trichogramma dendrolimi,like Trichogramma ostriniae,has a good control effect on Asian corn borer in the field.However,in the case of co-parasitism,Trichogramma dendrolimi can not complete its own development cycle,resulting in a decline in population.This study confirmed the control effect of Trichogramma dendrolimi on Asian corn borer,and provided basic theoretical data for the study of interspecific competition of Trichogramma.