Dynamics of Wolbachia populations in transfected lines of Trichogramma

Fluorescence in situ hybridization was tested to specifically detect symbio nts of the genus Wolbachia in Trichogramma and to allow for semiquantitativ e estimations of symbiont abundance. Extraction solutions used for horizont al transfers of symbionts contain a high abundance of Wolbachia but. Wolbac hia have a low and decreasing abundance in microinjected lines (transfected lines). Moreover, eggs of microinjected lines were shown to be polymorphic for the infection. In naturally infected lines, Wolbachia are localized at the posterior pole of the eggs; they are scattered during the early stages of larval development and then concentrated in the ovaries at the end of t he female pupal development. Scattering and concentration are probably not active but rather the result of replications or morphogenesis. Conversely, Wolbachia are not concentrated at the posterior pole of eggs in microinject ed lines. Comparison of the within-family and between-family variances of t he symbiont abundance in a microinjected line did not lead us to conclude t hat this character shows a genetic variability. (C) 2000 Academic Press.