Recent studies on the biology and taxonomy of Ophelimus maskelli
In recent years, several serious pests have invaded eucalyptus forests in the Mediterranean region and Southern Europe, such as Phoracantha semipunctata, Ctenarytaina eucalypti, Gonipterus scutellatus (EPPO A2 List) and Phoracantha recurva. The latest to appear were two species of gall-inducing wasps: Leptocybe invasa (EPPO Alert List) and Ophelimus maskelli (Hymenoptera: Eulophidae). Currently, both species are causing severe damage to eucalyptus, in particular to Eucalyptus camaldulensis which is the most important species planted in the Mediterranean region and the Middle East. Studies were recently done in Israel on the taxonomy and biology of both L. invasa and O. maskelli. Although the taxonomy of Ophelimus is poorly known, it is now considered that the species which has been introduced into the Euro-Mediterranean region is Ophelimus maskelli and not O. eucalypti (which is also an invasive species in New Zealand after a probable introduction from Australia). Similarly, earlier records of gall-inducing wasps on eucalyptus identified as Aprostocetus sp. are now attributed to Leptocybe invasa.
Leptocybe invasa
L. invasa was first observed in the Middle East in 2000 and later described as a new genus and species. In Israel, L. invasa has 2 to 3 overlapping generations and reproduces by thelytokous parthenogenesis. At Bet Dagan, development time from oviposition to emergence was approximately 4.5 months. They form typical bump-shaped galls on the leaf midribs, petioles and stems of new growth of several eucalyptus species. In Bet Shan Valley where L. invasa has reached epidemic levels, juvenile shoots were often killed due to egg overloading. In Jordan valley, galls could be found on almost all leaves within trees. It is also stated that planting of E. camaldulensis was stopped because of extensive attacks by this insect.
Ophelimus maskelli
O. maskelli has 3 generations per year. Peaks of flight occur in spring when many young leaves are available. O. maskelli prefers to oviposit in developed, immature leaves, on the leaf blade near the petiole (whereas L. invasa prefers the mid-rib, petioles and newly developed twigs). Females lay an average of 109 eggs. The gall diameter ranged from 0.9 to 1.2 mm and gall density from 11.5 to 36 galls per cm². The typical colour of the galls (greenish-yellow or light to dark purple) appeared as soon as the third instar larva develops. In these studies, among the 84 eucalyptus species tested, 14 were found to be suitable hosts (including species which are widely used in the Mediterranean region such as: Eucalyptus camaldulensis, E. globulus, E. grandis, and E. tereticornis). Heavy leaf galling by O. maskelli results in premature shedding of the leaves soon after adult emergence. In Israel, high populations of O. maskelli have been observed in the coastal plain and the Judean foothills, where 80-year-old trees had almost completely lost their foliage. In addition, during peak emergence periods O. maskelli can be a nuisance to humans by forming ‘clouds’ of wasps.
In Israel, both O. maskelli and L. invasa occur at epidemic levels and galls of the two species are often found on the same leaves. Observations tend to suggest that O. maskelli is a better competitor which could displace L. invasa. Research continues on the identification and use of parasitoids to control these eucalyptus gall wasps.
Sources
Mendel Z, Protasov A, Fisher N, La Salle J (2004) The taxonomy and natural history of Leptocybe invasa (Hymenoptera: Eulophidae) gen. ; sp.nov., an invasive gall inducer on Eucalyptus. Australian Journal of Entomology 43, 101-113.
Protasov A, La Salle J, Blumberg D, Brand D, Saphir N, Assael F, Fisher N, Mendel Z (2007) Biology, revised taxonomy and impact on host plants of Ophelimus maskelli, an invasive gall inducer on Eucalyptus spp. in the Mediterranean area. Phytoparasitica 35(1), 50-76.