Trace of symbiotic bacterial infection in Japanese pine sawyer Monochamus alternatus

Abstract

Insects carry various endosymbiotic bacteria which can affect the reproductive capabilities of their hosts. Wolbachia is a common and widespread group of intracellular symbiotic bacteria found universally within various groups of arthropods and nematodes. They manipulate insect host reproduction by causing cytoplasmic incompatibility, feminization, male killing or parthenogenesis. The ability of Wolbachia to cause reproductive alteration drives their efficient and rapid spread in host populations. Monochamus alternatus is the longicorn beetle notorious as spreading the pine wilt disease as a vector of the pathogen, pinewood nematode. In previous studies, a Wolbachia gene was detected in M. alternatus, suggesting that this insect has been infected with Wolbachia. However, subsequent studies revealed that M alternatus was not infected with Wolbachia but had many Wolbachia genes on an autosome, indicating that lateral gene transfer from Wolbachia to M. alternatus has occurred. The findings suggest that the Wolbachia endosymbiont that had infected M. alternatus have disappeared from the insect, leaving part of its own genome. This review highlights the interesting association of Wolbachia with M. alternatus as indicated by recent studies and proposes the future directions of research on this topic.