Oogenesis in the date stone beetle, Coccotrypes dactyliperda, depends on symbiotic bacteria

It has been suggested that sex ratio distorting symbionts are involved in the sex determination and female-biased sex ratios observed in strongly inbred scolytid beetles. Coccotrypes dactyliperda (Coleoptera: Scolytinae) is a species in which mother-son- and sib-mating occur inside the date seeds it inhabits, and the sex ratios produced are highly skewed toward females. In the present study, polymerase chain reaction (PCR) techniques and antibiotic treatments are applied to determine the possible role of Bacteria in this system. PCR with primers specifically designed to target the 16S rDNA gene in all Bacteria reveals the presence of Wolbachia and Rickettsia in control beetles, but not in antibiotic-treated individuals. Virgin females fed with antibiotics lay no eggs, and no sign of oogenesis is detected compared with all-male progeny of virgin control females. Mated females fed with antibiotics lay significantly fewer eggs than control females, with a strong effect of female age at the time of antibiotic feeding on the number of eggs laid. The study suggests that symbiotic bacteria are not involved in female-biased sex ratios but are required for oogenesis in C. dactyliperda. The specific role each of the bacteria (Wolbachia and Rickettsia) plays in the oogenesis remains to be determined.