Endosymbionts as a substitute for the paternal genome in asexual haplodiploid insects

In haplodiploid insects, such as bees, ants and wasps, females develop from fertilized (diploid) eggs and males from unfertilized (haploid) eggs. Sometimes bacteria that live inside the cells of the insect, so-called endosymbionts, can induce asexual reproduction by which females develop from unfertilized diploid eggs. The infected insects do not mate and produce only daughters, that further transmit the bacteria to future generations. This thesis provides novel insight into how endosymbionts exploit the sex determination pathway of their host to induce asexual reproduction. I investigated two parasitoid wasps, Leptopilina clavipes and Asobara japonica, that have sexual populations as well as asexual populations infected with the bacterium Wolbachia. My results indicate that sex determination in L. clavipes does not rely on the allelic status of a complementary sex determination gene, similar to A. japonica, but contrary to, for example, the honeybee. Next, I compared Wolbachia's interference with the sex determination of both species. I found that Wolbachia alters the transcripts of the essential sex determination gene transformer (tra) during oogenesis and that this depends on Wolbachia titer. My findings indicate the generation of a feminization signal by the bacteria in the ovaries of the wasp. My study reveals how an endosymbiotic bacterium can ensure female development of its host without a paternal contribution to the egg.