A review on invasive gall-forming wasps that threaten non-native Eucalyptusplantations by researchers in the Tree Protection Co-operative Programme in FABI appears in Agricultural and Forest Entomology. The researchers profile several species of likely Australian origin that have established on non-native Eucalyptusplantations globally and discuss various challenges to their management.
The review by Dr Gudrun Dittrich-Schröder and others highlights the small number of described and known phytophagous Hymenoptera associated with Eucalyptus recorded in the Australian Plant Pest Database. According to the authors, thousands of hymenopteran species remain undescribed and therefore have the potential to invade other parts of the world.
“Given the importance of gall-forming hymenopterans as current and future pests of Eucalyptus, knowledge on the distribution and diversity of current invasive gall wasps as well as an understanding of the challenges associated with new introductions will be of value to inform responses to these threats,” motivate the authors.
Though they are successful invaders outside their native range, gall-formers are not significant pests in Australia. The researchers list the gall-formers’ ability to circumvent host defences, concealment from detection, the absence of their natural enemies and parthogenetic reproduction as some of the attributes that have made them such successful invaders.
“Species are often described for the first time once they become invasive and are of economic concern as is evident by the invasive gall-formers associated with Eucalyptus,” the authors argue. They point to a “paucity of records” in their native range, where the existence of some species was unknown before they were introduced outside of Australia.
“Such a paucity of records reflects the lack of economic importance of this group in Australia and that knowledge on the identity, diversity and biology of the endemic Eucalyptusgall-forming Hymenoptera is sparse.”
Several of these species lack taxonomic descriptions, contributing to challenges in their identification and classification. These challenges have resulted in “numerous instances of misidentification, misunderstanding of trophic levels and re-classification,” warn the authors.
“Sixteen Hymenoptera species have been recorded as invasive alien Eucalyptus gall?formers of likely Australian origin,” write the authors. Thirteen of these have established in more than 40 countries. Nearly 80 percent of these “became invasive in the last two decades, none of which were unknown in their native range before they were encountered as alien invasive.” The greatest diversity is found in Europe, North America and Africa.
The invasive gall-former species profiled by the researchers are:
- Of the eight Aprostocetus species associated with galls on Eucalyptus,Aprostocetus nigrithorax wasconfirmed as a gall-former;
- Epichrysocharis burwell was reported for the first time in Portugal but has not been found in Australia;
- Leprosa milgawas first reported galling seed capsules of Eucalyptus in South Africa and has since established in Italy. The authors state that it has an “ambiguous relationship” to Quadrastichodella nova and Moona spermophaga;
- Alhough absent from New Zealand, Leptocybe invasa has been reported in all the continents where Eucalyptus is planted;
- There is no “clear evidence” that Megastigmus eucalypti is either a primary galler or an invasive species;
- Megastigmus zebrinushas been recorded as an ectoparasitoid in Leptocybe galls in South Africa;
- Moona spermophaga was reported in 2000 in Argentina;
- Nambouria xanthops was discovered in New Zealand in 1999;
- Ophelimus migdanorum was detected in Chile in 2003;
- Ophelimus mediterraneus was observed in France in 2010 and since has been reported in Italy and Portugal;
- Two cryptic invasive lineages of Ophelimus eucalypti were recorded in New Zealand;
- With an adventive range spanning 25 countries, Ophelimus maskelli is the second-most widely distributed species;
- Quadrastichodella nova was described in Australia 22 years before it became invasive out of that country with nine of ten species native to Australia
- Selitrichodes globulus has not been recorded in Australia but was first discovered in California in the US in 2008.
The authors suggest that applying molecular techniques can complement taxonomic data and accelerate species identification, which will contribute to the successful implementation of biological control and phytosanitary regulations.
“Molecular data can be combined effectively with traditional taxonomic data by the establishment of databases or ‘reference sequence libraries’ which contain sequences of specimens that have been identified based on morphology,” write the authors.
They cite the Forest Insect Mitochondrial Database developed in the Forestry and Agricultural Biotechnology Institute as a tool where the identity of specimens can be established or linked to sequences within the database of identified species.