The effect of Wolbachia on diapause, fecundity, and clock gene expression in Trichogramma brassicae (Hymenoptera: Trichogrammatidae).

The short day lengths of late summer in moderate regions are used to induce diapause in various insects. Many studies have shown the maternal effect of photoperiod on diapause induction of Trichogramma wasps, but there is no study to show the relationship between photoperiodic regimes and clock genes in these useful biological control agents. Here, we investigated the role of photoperiods on diapause, fecundity, and clock gene expression (clk, cyc, cry2, per, and timeout) in asexual and sexual Trichogramma brassicae as a model insect to find any differences between two strains. Asexual strain was infected by Wolbachia, an endosymbiont bacterium. The diapause percentage was significantly higher under short days (8 h in sexual and 12 h in the asexual T. brassicae), although the diapause percentage of the sexual strain was significantly higher than the asexual one in all the photoperiods. The ANOVA revealed no significant changes between different photoperiods in the clock gene expression in the sexual strain but significant photoperiodic changes in clk, cyc, and timeout in the asexual strain. Our results showed that the mRNA levels of clock genes of asexual T. brassicae were significantly lower than those of sexual strain. The fecundity was significantly higher in the asexual strain. These results suggest that Wolbachia infection makes disturbance on the clock gene expression which consequently reduces the percentage of diapause but increases the fecundity in asexual T. brassicae.