Invasive gall-forming wasps that threaten non-native plantation-grown Eucalyptus : diversity and invasion patterns

Abstract

Gall‐forming hymenopterans of Eucalyptus species are highly successful invaders causing significant damage in non‐native plantation forests. To date, at least 16 of these species have been recorded as invasive eucalypt gall formers, of which less than half are known from Australia where they are thought to be native. About 80% of the species have become invasive only in the last two decades, <10%, of which were known from Australia beforehand. Two species, Leptocybe invasa and Ophelimus maskelli are global invaders that have become established in 43 and 23 countries, respectively, since 2000. They belong to a large number of wasps that cause similar damage and that could become invasive in the future. The problem of identification is exacerbated by the fact that many species lack taxonomic descriptions; over 80% of the invasive eucalypt gall wasps were first described from their invasive range. The small number of taxonomists able to identify these insects slows accurate diagnoses. Even when initial identifications have been made, these may be confused with morphologically similar but distinct cryptic species, which may differ in their host range and natural enemy interactions. Furthermore, detailed information regarding their biology and native distribution is typically sparse or unknown. This lack of information delays the initiation of management actions because breeding for resistance and biological control requires accurate identification of the target pest. The gall‐forming hymenopterans associated with Eucalyptus represent an important group on which to focus the development of pre‐emptive quarantine, monitoring and potential management options. Given the global nature of invasions by these insects, an international and collaborative research approach is required, where knowledge and tools for study can be shared in a more effective manner.