First report of the Eucalyptus gall wasp, Ophelimus maskelli (Hymenoptera: Eulophidae), an invasive pest on Eucalyptus, from the Western Hemisphere.

Ophelimus maskelli (Ashmead) (Hymenoptera: Eulophidae) was found in southern California, USA, on March 17, 2014, in Riverside County, University of California Riverside Campus (UCR), and has been common there since then. It has also been found in other locations in southern California, including San Diego County (San Diego Safari Park on November 1, 2014), and Orange County (Laguna Niguel Regional Park). Specimens collected from UCR were compared with voucher specimens of O. maskelli collected from Lazio, Italy, and were found to be conspecific. This represents the first report of O. maskelli from the Western Hemisphere. Ophelimus maskelli is a uniparental leaf-gall inducing invasive pest of several Eucalyptus species of the Exsertaria, Latoangulata, and Maidenaria sections (Protasov et al. 2007a). Ashmead’s (1900) description of O. maskelli from New Zealand is its only report from that country. Instead, O. maskelli has been observed on Eucalyptus in New South Wales, Australia (Protasov et al. 2007a), and therefore is probably native to Australia. Its morphology and taxonomic history were reviewed recently by Protasov et al. (2007a), and partial sequences of the cytochrome oxidase I mtDNA, 28S D2 rDNA, and 18S rDNA of Italian specimens were obtained as part of a review of the higher systematics of Eulophidae (Burks et al. 2011). Other species of leaf-gall inducing Eulophidae are known from California (Schauff & Garrison 2000; La Salle et al. 2009), all from the diverse and widespread subfamily Tetrastichinae. While subjectively similar to these species morphologically, O. maskelli (Fig. 2) is only distantly related to them, in the entirely gall-associated subfamily Opheliminae native to Australia, New Guinea, and New Zealand (Bouček, 1988). Morphological features distinguishing O. maskelli from gall-inducing Tetrastichinae include shape of the marginal vein and parastigma of its fore wing, the lack of submedian grooves on its mesoscutellum, and the presence of 4 anelli followed by a larger preclaval flagellomere in its antenna. It differs from most other species of Ophelimus Haliday in having only a single seta on its submarginal vein (Protasov et al. 2007a). Ophelimus maskelli was first recorded as an exotic pest in 1999 in Italy, where it was misidentified as Ophelimus eucalypti (Gahan) (Arzone & Alma 2000). It has since been found in several other regions where Eucalyptus is grown, including the Mediterranean Basin, but also Indonesia, South Africa, and Vietnam (Mendel et al. 2004, 2005; EPPO 2006; Lawson et al. 2012). Although not reported previously from the Western Hemisphere, the constant spread of many other pests of Eucalyptus to California indicated that it might soon be found there (Paine et al. 2011). Uncontrolled populations of O. maskelli rapidly reached high densities in Israel (Mendel et al. 2007). They caused severe leaf damage and early leaf drop that resulted in almost complete defoliation of mature trees in some cases, and populations reached high enough densities to disrupt everyday human activities, even disrupting the harvest of other crops. Eucalyptus camaldulensis Dehnhardt and Eucalyptus tereticornis Smith are economically important species that are particularly susceptible to attack by O. maskelli, but other economically important species of Eucalyptus are susceptible to a lesser extent (Protasov et al. 2007a). Galls produced by O. maskelli are blister-like galls that can cover nearly all of a leaf’s surface (Fig. 1). The Australian uniparental parasitoid Closterocerus chamaeleon (Girault) (Eulophidae) has been used to effectively control O. maskelli in the Mediterranean Basin (Laudonia et al. 2006; Rizzo et al. 2006; Mendel et al. 2007; Protasov et al. 2007b; Caleca et al. 2011). Control programs in Israel included release of Stethynium ophelimi Huber (Mymaridae), another Australian parasitoid reared together with C. chamaeleon, but which was not recovered in large numbers in subsequent surveys (Mendel et al. 2007). Closterocerus chamaeleon has since exhibited strong potential for independent expansion to populations of O. maskelli in distant areas (Caleca 2010; Caleca et al. 2011). The known host range of C. chamaeleon is limited to O. maskelli, but it is possible that other leaf-gall inducers on Eucalyptus may serve as hosts as well (Protasov et al. 2007b).