The PCR-DGGE was carried out using a semi-nested Rapamycin in vitro approach, as the bacterial primers targeting the V3-region are known to amplify eukaryotic DNA [52]. Three bands corresponding to these three endosymbionts recurred in all studied M. pygmaeus populations. The DGGE-profile of bacteria in the M. caliginosus populations were similar to those of M. pygmaeus, confirming the presence of Wolbachia and the Rickettsia strain from the ‘Limoniae’ group, but the bellii-like Rickettsia was not found (Fig. 2). A PCR using specific primers for each endosymbiont confirmed this result. The bands with lower density present in some populations corresponded to the Gamma-proteobacteria and Firmicutes. Most of these bands were attributed

to Serratia species of the Enterobacteriaceae family, which have been found in the gut of various insect orders, including Hymenoptera, Lepidoptera, Neuroptera and Hemiptera [53–56]. One band however (Fig. 2, no. 7), has been amplified in five wild Macrolophus populations. This band corresponded to an uncultured Gamma-proteobacterium, the role of which is unknown. The low bacterial diversity in the gut of M. pygmaeus may be attributed to its natural diet. A more diverse bacterial community is mostly detected in insects that consume nutritionally poor diets [57],

MK-2206 datasheet whereas the main food of Macrolophus bugs consists of nutrient-rich arthropod prey. Also, the microbial diversity of the investigated Macrolophus spp. may have been underestimated by the dominance of the endosymbionts in its host. Samples of the wild Macrolophus populations were collected in ethanol and DNA-extraction was performed on CYTH4 whole adults; gut dissections were thus only feasible for the two laboratory reared populations. The faint bands in the DGGE-profile of the wild populations of Macrolophus may originate from prey remnants in the gut. A PCR-DGGE profile of the gut of the laboratory populations of M. pymaeus and M. caliginosus established the presence of the Gamma-proteobacteria and the Rickettsia endosymbionts in M. pygmaeus (Fig. 3), whereas the gut of M. caliginosus was

only infected by R. limoniae. In both species, Wolbachia was virtually absent in the gastro-intestinal tract. The DGGE profile of the ovaries only indicated an infection by the Wolbachia and Rickettsia endosymbionts, suggesting that no other bacteria infected the reproductive tissues. A diagnostic PCR on adults and ovaries of M. pygmaeus and M. caliginosus confirmed that all individuals are multiple infected and that the endosymbionts are vertically transmitted, implying that the infections are fixed. A FISH analysis confirmed high densities of both Wolbachia and Rickettsia in the ovarioles of M. pygmaeus (Fig. 4 and 5), suggesting a high rate of vertical transmission to the progeny [58]. Wolbachia is the only endosymbiont infecting the studied Macrolophus spp. which is known to cause CI in its insect host [7].