Rickettsia-like maternally inherited bacteria have been shown to be involved in a variety of alterations of arthropod sexuality, such as female-biased sex ratios, parthenogenesis, and sterility of crosses either between infected males and uninfected females or between infected individuals (cytoplasmic incompatibility). We have characterized several of these microorganisms through partial sequences of the small (16S) and large (23S) subunit ribosomal DNA. All the symbionts identified, which include several cytoplasmic incompatibility microorganisms, several endosymbionts of terrestrial isopods, and symbionts of two thelytokous Trichogramma wasp species, belong to a monophyletic group of related symbionts, some of which have previously been detected in several insects exhibiting cytoplasmic incompatibility. Three molecular lineages can be identified on the basis of 16S as well as 23S sequences. Although they are only known as endocellular symbionts, Wolbachia spread by horizontal transfer across host lineages as evidenced by their diversification which occurred long after that of their hosts, and by the non-congruence of the phylogenetic relationships of symbionts and their hosts. Indeed, symbionts of two different lineages have been found in the same host species, whereas closely related endosymbionts are found in distinct insect orders. Isopod endosymbionts form a separate lineage, and they can determine feminization as well as cytoplasmic incompatibility. The ability to determine cytoplasmic incompatibility, found in all lineages, is probably ancestral to this group.

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Rickettsial symbionts of the genus Wolbachia, harboured by many arthropod species, are implicated in feminization, cytoplasmic incompatibility and parthenogenesis phenomena. These symbionts induce thelytokous parthenogenesis in some egg parasitoids of the Trichogramma genus. In our study of these minute wasps, puri¢ed Wolbachia from an infected species, T. pretiosum, were transferred by microinjection into in vitro developed pupae of an uninfected species,T. dendrolimi. We believe this to be the ¢rst successful transfer of Wolbachia in parasitoids. The presence or absence of Wolbachia was determined using DAPI staining, PCR and ftsZ gene sequencing. An ftsZ gene fragment from microinjected T. dendrolimi was shown to be identical to that of T. pretiosum, con¢rming that transfer was successful. Wolbachia were still present in the recipient species 26 generations after the transfer, although only partial induction of thelytoky was observed. Therefore, in Trichogramma, density of symbionts or symbiont^host interactions may be involved in the expression of parthenogenesis. The successful transfer of the symbiont within the Trichogrammatidae, a group of insects used in biological control strategies, could increase their agronomic importance by manipulating their reproductive system.

International audienceA molecular key for the identification of common Trichogramma (Hymenoptera: Trichogrammatidae) species found in agricultural settings around the Mediterranean is developed based on the sequence of the internal transcribed spacer 2 of the ribosomal cistron. Using the size of the ITS2 PCR product and restriction fragment length polymorphisms of the amplicon, ten Trichogramma species (T. bourarachae Pintureau and Babault, T. brassicae Bezdenko, T. cacoeciae Marchal/T. embryophagum Hartig, T. cordubensis Vargas and Cabello, T. dendrolimi Matsumura, T. euproctidis Girault, T. evanescens Westwood, T. nerudai Pintureau and Gerding, T. oleae Voegelé and Pointel, and T. pintoi Voegelé) can be distinguished

International audienceLienDigitalObjectIdentifier http://dx.doi.org/10.1007/s10340-010-0327-0 LienArticle http://www.springerlink.com/content/g98685852816p827

Each individual of all populations of the thelytokous species Trichogramma cordubensis is infected by Wolba! chia[ Populations are composed of females\ a few rare males and some intersexual or gynandromorphic individuals often capable of normal reproduction as females[ Antibiotic "minocycline# and high temperature "29>C# treatments inactivate Wolbachia and induce male production[ After these treatments\ the sex ratio depending on the remaining frequency of thelytoky shows a genetic variability[ E}ect of cycles with and without treatments "minocycline or 29>C# on the thelytokous reproduction of {individuals| "one {individual| being one Trichogramma ¦n Wolbachia# was studied[ The resistance of thelytokous reproduction to 29>C but not to minocycline\ probably due to Wolbachia genes\ increased[ It is concluded that potentialities of adaptation to high temperature exist in Wolbachia and can explain a part of the spreading of these symbionts among host populations[

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Wolbachia are symbiotic bacteria altering reproductive characters of numerous arthropods. Their most recent phylogeny and classification are based on sequences of the wsp gene. We sequenced wsp gene from six Wolbachia strains infecting six Trichogramma species that live as egg parasitoids on many insects. This allows us to test the effect of the addition of sequences on the Wolbachia phylogeny and to check the classification of Wolbachia infecting Trichogramma. The six Wolbachia studied are classified in the B supergroup. They confirm the monophyletic structure of the B Wolbachia in Trichogramma but introduce small differences in the Wolbachia classification. Modifications include the definition of a new group, Sem, for Wolbachia of T. semblidis and the merging of the two closely related groups, Sib and Kay. Specific primers were determined and tested for the Sem group.