Sex allocation and larval competition in a superparasitizing solitary egg parasitoid: competing strategies for an optimal sex ratio

1. Parasitic Hymenoptera reproduce by arrhenotokous parthenogenesis, and fe males of these species are able to control their progeny sex ratios. In str uctured populations of parasitic Hymenoptera, primary sex ratios are often highly biased toward females. However, sex ratio can be adjusted to the qua lity of encountered patches or hosts or be modified by differential develop mental mortality. 2, In this paper, the effects were evaluated of the quality of encountered hosts and developmental mortality on the sex ratio in Anaphes victus, a sol itary egg parasitoid whose first instar larvae present a sexual dimorphism and where superparasitism is regulated by larval fights between first insta r larvae. 3. The results showed that a female-biased sex ratio is allocated to unpara sitized hosts. In the presence of parasitized hosts, the second (superparas itizing) female produced a significantly higher sex ratio than the first fe male but the tertiary sex ratio (sex ratio at emergence) was not significan tly different from the sex ratio produced with unparasitized hosts. The inc rease in the primary sex ratio produced by the second female was mostly com pensated by the higher mortality of male larvae.