| Wolbachia is a genus of endosymbiont bacteria that can be found in the tissues of arthropods and nematodes. Wolbachia could be transfected vertically and horizontally among invertebrates species. Wolbachia has evolved various mechanisms to manipulate reproduction of their hosts, inducing cytoplasmic incompatibility, parthenogenesis induction, feminization and male killing. To increase the female offspring rate and reduce the cost of production, thelytokous strains of Trichogramma could be a better choice in the biological control. The external environment and endosymbiont bacteria have obvious influence on the fitness of Trichogramma. Wolbachia infection is common among Trichogramma dendrolimi Matsumura and cause the thelytoky parthenogenesis. Making clear of the effect of Wolbachia on the biology and ecology of T. dendrolimi could contribute to the widely practice of thelytokous strains of T. dendrolimi in biological control.To explore the effects of Wolbachia on host development, fertility and competitiveness, T. dendrolimi was used in this research which reared in Antheraea pernyi eggs and Corcyra cephalonica (Stainton) eggs. To explore the effects of ultraviolet radiation on thelytokous strain of T. dendrolimi Matsumura, ultraviolet irradiation were used to explore the influence of different radiation time on the effect of removing Wolbachia. Fecundity, longevity and sex ratio were determined to make sure the influence of different radiation time on the fitness of T. dendrolimi. Furthermore, to make sure the impact of Wolbachia on the competitiveness of T. dendrolimi, we investigated difference of the two strains in fitness and competitive ability, by using the competition experiment of C. cephalonica (Stainton) eggs between thelytokous and arrhenotokous strains of T. dendrolimi.The results were as follows:1. The result of different ultraviolet radiated time on the host eggs indicated that, ultraviolet radiation can remove Wolbachia in some thelytokous strain of T. dendrolimi. But the Wolbachia could be detected in the next generation if the ultraviolet radiation was removed, it indicated that ultraviolet radiated could remove just the Wolbachia in contemporary thelytokous strain of T. dendrolimi. Compared with 5min radiation,12min radiation to thelytokous strain of T. dendrolimi which reared in C. cephalonica eggs, could decrease the female proportion from 0.890 to 0.829 (P<0.05), PCR detection indicated that ultraviolet radiation 5min could remove Wolbachia in 60% thelytokous strain of T. dendrolimi, higher than 20% with ultraviolet radiation of 12min and more than 12min of radiation would kill T. dendrolimi. In the thelytokous stain of T. dendrolimi which reared in A. pernyi eggs, there was no significant difference in female proportion of T. dendrolimi with ultraviolet radiation of different times (P>0.05). PCR detection indicated that ultraviolet radiation 38min and 40min could remove Wolbachia in 40% thelytokous strain of T. dendrolimi,42min and 45min could remove Wolbachia in 20% thelytokous strain of T. dendrolimi and more than 45min of radiation would kill the T. dendrolimi.2. Comparison of different time to fitness. The fitness of T. dendrolimi with different ultraviolet radiation time were compared, and the result were as follows. The fecundity, development time, life span of T. dendrolimi were significantly reduced by ultraviolet radiation (P>0.05). Compared with control group without radiation,12min radiation to thelytokous strain of T. dendrolimi which reared in C. cephalonica eggs, could decrease the egg parasitism from 48.45% to 12.90% (P<0.05), the adult emergence rate declined from 69.89% to 50.94%(P<0.05), and the adult longevity declined from 8.40d to 3.45d (P<0.05). Compared with control group without radiation,45min radiation to thelytokous stain of T. dendrolimi which reared in A. pernyi eggs, could decrease the number of wasps of per host egg from 93.10ind. to 56.95ind. (P<0.05), development time declined from 17.90d to 15.15d (P<0.05), and adult longevity declined from 14.20d to 4.15d (P<0.05). Male individuals could be found in next generation and the sex ratio of next generation had no significant difference.Compared the fitness of T. dendrolimi between the Wolbachia removed generation and next generation, the result indicated that, development time and life span thelytokous stain of T. dendrolimi were significantly decreased (P<0.05). In the thelytokous strain of T. dendrolimi which reared in C. cephalonica eggs, Wolbachia removed could resulted to development time declined from 9.8d to 8.5d (P<0.05), and the adult longevity declined from 8.40d to 4.8d (P<0.05). In the next generation of T. dendrolimi which has been removed Wolbachia, adult longevity was 6.00d and development time was 9.90d. In the thelytokous stain of T. dendrolimi which reared in A. pernyi eggs, Wolbachia removed could resulted to declined development time from 17.95d to 14.50d, and the adult longevity declined from 14.20d to 4.00d, in the next generation of T. dendrolimi which has been removed Wolbachia, adult longevity was 9.10d and development time was 18.00d. There was no significant difference in fertility of T. dendrolimi which reared in two kinds of host eggs (P>0.05).3. To investigate the effect of Wolbachia on the competition ability of T. dendrolimi and the potential application of thelytokous stain of T. dendrolimi in the production practice, the effect of competition on C. cephalonica eggs between thelytokous and arrhenotokous strains of T. dendrolimi were detected.The result indicated that, the age of T. dendrolimi and the age of C. cephalonica eggs could influence the parasitism rate, emergence rate, dead offspring number of T. dendrolimi and hatched number of rice moth egg. Furthermore, Wolbachia could display mutualistic and parasitic in females. Under the lower competition pressure, in the mixed group, the emergence number of thelytokous strain of T. dendrolimi could up to 18.83ind., which was higher than the arrhenotokous strain of T. dendrolimi (16.10ind.). This result indicated that thelytokous strain of T. dendrolimi has stronger competition, and the Wolbachia appear to be mutualistic. But under the condition of higher competition, the emergence number of thelytokous strain of T. dendrolimi was only 2ind. or 3ind., which was significant lower than the 14ind. to 16ind. of arrhenotokous strain of T. dendrolimi. This result indicated that arrhenotokous strain of T. dendrolimi has stronger competition, and the Wolbachia appear to be parasitic. |
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