Host discrimination and factors affecting incidence of superparasitism in hemiptarsenus varicornis (Hymenoptera: Eulophidae), a parasitoid of the leafminer liriomyza trifolii (Diptera: Agromyzidae)

An ovipositing parasitoid can save searching time, energy and eggs by avoiding superparasitism, and superparasitism avoidance hence is a factor that affects searching efficiency of a parasitoid. This study examined host discrimination and environmental factors causing superparasitism in the solitary parasitoid wasp Hemiptarsenus varicornis, a promising candidate for biological control of dipteran leafminers such as Liriomyza trifolii and L. sativae. Cage experiments showed that the pattern of parasitoid egg distributions among hosts skewed significantly from the Poisson distribution. This suggested that H. varicornis had the host-discrimination ability. However, superparasitism avoidance was not perfect; hosts that had received two parasitoid eggs were observed. Accordingly, factors affecting the incidence of superparasitism were examined. Superparasitism was observed only for third host larval instars, the most suitable host stage for parasitoid development. Superparasitism occurred more frequently when females laid more eggs, suggesting that females with a greater motivation to oviposit were more likely to superparasitize. The level of superparasitism also increased when fewer numbers of third host instars were available for females. The number of second instars of L. trifolii available did not affect superparasitism incidence on third host instars. Host discrimination and superparasitism in H. varicornis are discussed in terms of its searching efficiency and mass-rearing procedure.