Cotesia flavipes Cameron (Hymenoptera: Braconidae) does not exhibit complementary sex determination (ii) Evidence from laboratory experiments

Sex determination in the order Hymenoptera is based on haplodiploid arrhenotoky; in which males develop from unfertilized eggs and are haploid, whereas females develop from fertilized eggs and are diploid. However, some hymenopteran species produce diploid males through a mechanism known as single-locus complementary sex determination (sl-CSD). In these species, heterozygous individuals at a single sex locus develop into females, whereas hemizygotes (haploids) and homozygotes (diploids) develop into males. Inbreeding leads to homozygosity and consequent production of diploid males. We investigated the presence of sl-CSD in the braconid Cotesia flavipes using a series of inbreeding crosses among five isofemale lines. Sex ratio (proportion of females) did not differ among the within-line crosses, between-line crosses and crosses carried out between isofemale lines and a mixed (outbred) colony. Brood size of within-line and between-line crosses did not differ. Culturing populations for 25 generations did not result in changes to more male-biased sex ratios. We conclude that CSD does not exist in C. flavipes. The implications of absence of CSD in C. flavipes are discussed in context of mass rearing for classical biological control programmes.