Distribution, Transmission And Function Of Rickettsia In Eretmocerus Havati

The whitefly, Bemisia tabaci, is a species complex including at least36cryptic species. Mediterranean (MED) and Middle East-Asia Minor1(MEAM1) are the most invasive pests among the species complex. They have invaded many countries and regions and displaced many indigenous species. What’s more, they have caused considerable damage to agriculture and horticulture and become notorious global pests. The insect symbionts, as the microorganism lived in the insects’body, play an important role in insects’biological characteristics and resistance to poor environment. Both the MEAM1and MED whitefly in our lab harbor the primary symbiont Portiera, but MEAM1also harbors a secondary symbiont Rickettsia, whereas MED whitfly doesn’t. Symbionts in parasite wasps of whitefly have been detected and may influence the biological efficiency of the wasps. Eretmocerus hayati, as the obligate parasitic wasp of B. tabaci, is one of the most effective natural enemies used to control whitefly. Thus the study on the symbionts in Eretmocerus hayati would provide the important information for the use of this wasp. In this study, the symbiont Rickettsia was identified in E. hayati and its distribution, transmission route and function were studied.(1) The identification and distribution of symbiont Rickettsia in E. hayatiThe bacterial16S rRNA gene was amplified using the universal primers to study how many kinds of bacteria in the wasp reared on MEAM1whitefly. PCR fragments were purified and ligated into the pGEM-T Easy Vector (Promega, USA) and sequenced and compared on the NCBI. Eventually the symbiont Rickettsia was detected in the wasp Eretmocerus hayati, which was100%homology with Rickettsia in MEAM1whitefly. Using the DNA and cDNA of Eretmocerus hayati as the template and the Rickettsia distinctive16S rRNA primers, the symbiont was further verified. What is more, the result of FISH indicated that Rickettsia located in the wasp’s abdominal gut.(2) The vertical and horizontal transmission of RickettsiaWasps from MEAMI whitefly (Wb) harbor Rickettsia, whereas those reared from MED whitefly contain no Rickettsia. When Wb wasps were used to parasitize MED whitefly, the eggs of Wb and F1adults (Wb-Q-F1) were failed to detected any Rickettsia, which proved that Rickettsia can’t transmit vertically in Eretmocerus hayati. When Wq were used to parasitize MEAM1whitefly for24h, PCR test results showed that90.8%of F1adults of Wq (Wq-B-F1) and46.4%of Wq tested (Wq-B-24h) carried Rickettsia. Among wasps of Wq-B-24h,72.9%females carry Rickettsia while no males was detected carrying Rickettsia. FISH test showed that Rickettsia in both Wq-B-24h and Wq-B-F1located in the wasp’s abdominal gut. The wasps of Wq-B-F1and Wq-B-24h were further fed with honey (without Rickettsia) for several days and the symbiont Rickettsia were tested again. PCR results showed that Wq-B-F1still carried Rickettsia after feeding with honey for3and6days while Wq-B-24h didn’t carry Rickettsia any more after feeding with honey for3days. This result indicates that, Rcikettsia can transmit from host to parasite wasps through horizontal transmission at different trophic level, but vitality of symbiont by different transmission routes differed.(3) Comparison of biological characteristics between Wq and WbFour experimental combinations were designed for the comparsion of biological characteristics between Wb and Wq:Wb-B (Wb parasitize MEAM1whitefly); Wq-B (Wq parasitize MEAM1whitefly); Wb-Q (Wb parasitize MED whitefly); Wq-Q (Wq parasitize MED whitefly). The number of oviposition, rate of parasitism, developmental duration and female ratio of each treatment were compared. The results showed that the number of oviposition had no significant differences between Wb-B and Wq-B or between Wb-Q and Wq-B, but significant differences were found between Wb-B, Wq-B and Wb-Q, Wq-Q. For the rate of parasitism and developmental duration, no significant differences were found between these four treatments. However, for the female ratio, Wq-Q was significant different with Wb-B, Wq-B and Wb-Q. This implies that Rickettsia may have no effect on the wasp’s number of oviposition, rate of parasitism and developmental duration, but may have some effcts on the female ratio of this wasp.