A first record of egg parasitism in Orius laevigatus: the parasitoid Erythmelus funiculi disrupts biological control in pepper

Abstract: Since more than two decades, biological control became a commercial standard in
greenhouse sweet pepper operations in Israel and the anthocorid predatory bug Orius laevigatus plays a key role in this system. In the past few years, a puzzling phenomenon has been observed: after a successful establishment, O. laevigatus populations gradually decrease. The age distribution becomes biased towards adults and eggs, with relatively few nymphs. In many cases, the predator population collapses, despite repeated releases. Preliminary work has shown that this was not due to chemical sprays, lack of alternative food or reduced survival, fertility or fecundity of the predators. A few years later, a minute parasitic wasp has been observed at the vicinity of O. laevigatus eggs on the crop, parasitizing the eggs. The wasp was identified as Erythmelus funiculi (Mymaridae), the first host record for this species.
Bioassays have confirmed that E. funiculi can successfully parasitize and complete its development in eggs of O. laevigatus. An extensive field monitoring program has demonstrated that the parasitoid occurs in the main cultivation areas – the arid Negev and Arava regions in Israel’s south. Parasitism was found in 17 of the 19 sampled farms, with an average parasitism rate of 52 ± 4 % per sample (mean ± se, n = 119). Parasitized Orius spp. eggs were found also in close proximity to pepper farms, on Verbesina encelioides plants, a wide-spread alternative host plant of Orius spp.
In the Negev region, where plantings start in January, E. funiculi penetrated the crop at the
end of April, as natural vegetation, including V. encelioides, started to wilt. In the Arava region, where plantings start in August, first egg-parasitism was recorded in October. Once the parasitoid entered the plots, parasitism rates increased to an average of 94 % within 6 weeks, corresponding to 2-3 E. funiculi generations. Implications on biological control and strategies to manage O. laevigatus egg-parasitism are discussed.