Infection density of Wolbachia and level of cytoplasmic incompatibility in the Mediterranean flour moth, Ephestia kuehniella.

Wolbachia, a causative agent of various reproductive changes in arthropods, induces cytoplasmic incompatibility (CI) in the Mediterranean flour moth, Ephestia kuehniella. Two strains of E. kuehniella, Yokohama and Tsuchiura, harbor closely related Wolbachia, but the Yokohama strain expresses stronger CI than the Tsuchiura strain. A transinfected E. kuehniella strain that harbors the Wolbachia derived from the almond moth Cadra cautella, expresses weak CI at a similar level to the Tsuchiura strain. In the present study, we measured the Wolbachia density in the testis of the three E. kuehniella strains in order to examine the effects of bacterial strain and infection load on the expression of CI. When individuals of the same strain were compared, a correlation of bacterial density to CI level was observed. In addition, the Wolbachia density was higher in the Yokohama strain than the Tsuchiura strain in agreement with the CI levels expressed. However, this relationship did not hold in the comparison between the naturally infected and transinfected strains that carried phylogenetically distant Wolbachia.