Ophelimus sp., a new invasive gall wasp of Eucalyptus globulus in Europe, escapes the parasitism by Closterocerus chamaeleon due to an asynchronous life cycle

Abstract

Ophelimus sp. (Hym: Eulophidae) is an Australian gall wasp newly found in Southern Europe forming galls on Eucalyptus globulus. A congeneric gall wasp O. maskelli, also established in the Mediterranean Basin, is currently controlled by the introduced parasitoid Closterocerus chamaeleon. To date, no parasitism was observed on Ophelimus sp. by C. chamaeleon. Here we analyze a possible escape from parasitism through an asynchronous life cycle in this host-parasitoid system. The ability of C. chamaeleon to oviposit and complete development on Ophelimus sp. was determined, both in laboratory and field experiments. Ophelimus sp. showed to be univoltine, with winter larval development and possible summer egg diapause, contrasting with the multivoltine behavior of O. maskelli, which completes 3–4 generations per year. Concomitantly, C. chamaeleon is normally collected in the field from May to October. In laboratory, under low temperatures (15 ± 1 °C), adults of the parasitoid could survive up to four months. Both old (86–89 days) and young (<16 days) parasitoid females showed similar parasitism behavior. Naïve parasitoid females oviposited in both O. maskelli (on E. camaldulensis) and Ophelimus sp. (on E. globulus), with no apparent preference between the two host species. We observed parasitism, when we exposed adults of C. chamaeleon to bagged eucalypt leaves infested with Ophelimus sp. galls, in field conditions. Altogether, our results demonstrate that C. chamaeleon is able to oviposit and complete development in Ophelimus sp. However, in field conditions, the lack of parasitism is possibly due to life cycle asynchrony between the parasitoid and the gall wasp.