Heterospecific ovicide influences the outcome of competition between two endoparasitoids, Encarsia formosa and Encarsia luteola

1. Studies of inter-specific competition in parasitoids have largely focused on the outcome of within-host competition and the behavioural mechanisms by which female parasitoids prevent competition. Another, less well studied, possibility is oviposition preceded by 'heterospecific ovicide', the destruction of the other species' egg. Heterospecific ovicide essentially eliminates within-host competition. 2. This study investigated the mechanisms and outcome of within-host competition in Encarsia formosa and Encarsia luteola, solitary endoparasitoids of whitefly pests. These species are known to commit ovicide of conspecific eggs. 3. Competition experiments indicated that the offspring of second-ovipositing females had an apparent advantage in competition, regardless of whether the second female was E. formosa or E. luteola. 4. Observations of ovipositor movement through the cuticle of host whitefly nymphs showed that both species often committed heterospecific ovicide and then oviposited or host-fed. Multiparasitism and heterospecific host discrimination were less common and absent respectively. 5. Heterospecific ovicide appears to explain the second-female advantage in competition between these species. Second-female advantage is contrary to the paradigmatic view of multiparasitism, where the first-ovipositing female has an advantage in competition or one of the species consistently prevails in competition.