1. ¹Laboratory of Applied Entomology and Zoology, Faculty of Agriculture, Ibaraki University, Ami, Ibaraki 300-0393, Japan
2. ²National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan

Correspondence: T Gotoh, Laboratory of Applied Entomology and Zoology, Faculty of Agriculture, Ibaraki University, Ami, Ibaraki 300-0393, Japan. E-mail: gotoh@mx.ibaraki.ac.jp

Received 19 November 2005; Accepted 10 July 2006; Published online 11 October 2006.

Abstract

Intracellular symbiotic bacteria belonging to the Cytophaga–Flavobacterium–Bacteroides lineage have recently been described and are widely distributed in arthropod species. The newly discovered bacteria, named Cardinium sp, cause the expression of various reproductive alterations in their arthropod hosts, including cytoplasmic incompatibility (CI), induction of parthenogenesis and feminization of genetic males. We detected 16S ribosomal DNA sequences similar to those of Cardinium from seven populations of five spider mite species, suggesting a broad distribution of infection of Cardinium in spider mites. To clarify the effect of Cardinium on the reproductive traits of the infected spider mites, infected mites were crossed with uninfected mites for each population. In one of the populations, Eotetranychus suginamensis, CI was induced when infected males were crossed with uninfected females. The other six populations of four species showed no reproductive abnormalities in the F₁ generation, but the possibility of CI effects in the F₂ generation remains to be tested. One species of spider mite, Tetranychus pueraricola, harbored both Cardinium and Wolbachia, but these symbionts seemed to have no effect on the reproduction of the host, even when the host was infected independently with each symbiont.