Abstract
A Japanese strain (DsTT1) of Diadegma semiclausum, an introduced parasitoid of the diamondback moth (DBM, Plutella xylostella), whose sex ratio is biased toward the male probably due to a low diversity in genes under single-locus complementary sex determination (sl-CSD), is inferior to normal-sex-ratio strains in terms of reproductive efficiency and the control effect against DBM. In an attempt to improve the sex ratio of the strain, we reintroduced a new strain from New Zealand (NZ). Although the sex ratio of the NZ strain (0.261) is similar to that of the DsTT1 strain (0.285), the mean sex ratios of four crossed lines of these strains (DsTT1 x NZ) (0.400-0.461) are significantly higher than those of the parent strains. The result indicates the presence of sl-CSD in D. semiclausum and suggests that the reintroduction of new strains can improve reproduction efficiency and control the effect against target pests in parasitoids whose sex ratio is biased toward the male due to sl-CSD.
