Wolbachia ¨C protected or not protected is the question
Kumm S, Moritz G
Martin-Luther-University Halle-Wittenberg, Developmental Biology, Domplatz 4, 06108 Halle, Germany.
Correspondence: sandra.kumm@zoologie.uni-halle.de
The last two decades revealed Wolbachia as one of the most widespread bacteria among arthropods. Bacteria of this genus are known to cause diverse reproductive manipulations in their hosts including cytoplasmic incompatibility, male killing, parthenogenesis, and feminization. In thrips females are usually diploid and males are haploid. The most common form of reproduction is arrhenotoky, but thrips also often reproduce by thelytoky. A couple of species are known to reproduce by thelytoky in some geographical areas, whereas the sex ratio values indicate arrhenotoky in other areas. Wolbachia was discovered in the thelytokous thrips species, Heliothrips haemorrhoidalis and Hercinothrips femoralis (Pintureau B et al. 1999. Annales de la Societe Entomologique de France 35: 416¨C420) and was proven to be responsible for thelytoky in Franklinothrips vespiformis (Arakaki N. et al. 2001. Proceedings of the Royal Society of London, Series B 268: 1011¨C1016). So far only thelytokous thrips species were tested. Therefore, in the present study we screened thrips species displaying different reproduction modes for the presence of Wolbachia using 16S rDNA and ftsZ gene primer. The thelytokous species Hercinothrips femoralis and Parthenothrips dracaenae possess Wolbachia and in H. femoralis Wolbachia was shown to be the reason for thelytokous reproduction since males were produced after antibiotic treatment. Males were also observed to copulate with females and spermathecae of females were filled with sperm. But it was not possible to generate an arrhenotokous line in H. femoralis. The arrhenotokous species Echinothrips americanus, Suocerathrips linguis, and Gynaikothrips ficorum also harbour Wolbachia, but the bacterium was not detected in Frankliniella occidentalis and Thrips tabaci. Neither thelytokous nor arrhenotokous populations of the latter species possess Wolbachia. Sequence analysis of three species, H. femoralis, P. dracaenae, and S. linguis, by direct sequencing confirmed the presence of Wolbachia, whereby all tested species are infected with different Wolbachia types. Antibiotic and heat treatment of thelytokous T. tabaci did not lead to male production and therefore bacteria are likely to exclude as being responsible for thelytoky in this species. Thus, it can be concluded that probably two different forms of thelytoky exist in Thysanoptera, one induced by microorganisms like in H. femoralis and a non-revertible (not induced by micro-organisms) like in T. tabaci. All positive tested species are no tospovirus vectors and species which do not possess the bacterium are known to act as tospovirus transmitters. Maybe there is some mechanism which protects tospovirus vectors from getting infected with Wolbachia or the opposite way around. It should be also proofed if and what influence Wolbachia has on arrhenotokous thrips species. Perhaps they also exhibit some kind of defence reaction against the bacterium suppressing the manipulation of reproduction.
