MOLECULAR EVIDENCE FOR SINGLE WOLBACHIA INFECTIONS AMONG GEOGRAPHIC STRAINS OF THE FLOUR BEETLE TRIBOLIUM-CONFUSUM

Infections with the rickettsial microorganism Wolbachia are cytoplasmi cally inherited and occur in a wide range of insect species and severa l other arthropods. Wolbachia infection often results in unidirectiona l cytoplasmic incompatibility (CI): crosses between infected males and uninfected females are incompatible and show a reduction of progeny o r complete inviability. Unidirectional CI can also occur when males ha rbouring two incompatible Wolbachia strains are crossed with females i nfected with only one of the two strains. In the flour beetle Triboliu m confusum, Wolbachia infections are of particular interest because of the severity of incompatibility. Typically, no progeny results from t he incompatible cross, whereas only partial incompatibility is observe d in most other hosts. Werren ct al. (1995a) reported that Wolbachia i nfections in T. confusum consist of two bacterial strains belonging to distinct phylogenic groups, based on PCR amplification and sequence a nalysis of the bacterial cell division gene ftsZ. However, Fialho & St evens (1996) showed that eight strains of T. confusum were infected wi th a single and common incompatibility type. Here we report analysis o f the ftsZ gene by specific PCR amplification. Diagnostic restriction enzyme assays revealed no evidence of double infections in 11 geograph ic strains of T. confusum, including the strain examined by Werren et al. (1995a). Further, sequence analysis of the Wolbachia ftsZ gene and an internal transcribed spacer (ITS) region in two of these strains d isplayed no nucleotide variation or evidence of polymorphisms. Results suggest that T. confusum is infected with B-group Wolbachia only.