Adult
Related invasive species
- Leptocybe invasa
Related Farm Practice
- Development
Leptocybe invasa is believed to be native to Australia or to the native range of its host plants Eucalyptus - Australia, New Guinea, Indonesia and Philippines -, although it has only been detected in Australia in Queensland and New South Wales. During the last two decades, L. invasa has spread worldwide, invading all the continents where Eucalyptus has been imported to (Asia, Africa, Europe, South and North America). The invasive potential of L. invasa is very high. Its broad host range, polyvoltinism, overlapping generations, concealed life style (galls) and reproductive modalities allow the pest to quickly spread and exponentially grow from few individuals. L. invasa is considered thelytokous because sex ratio of the most widespread lineage is female biased, but a biparental lineage also exists.
L. invasa females usually prefer newly developed leaves, where they lay their eggs in the midribs, petioles and parenchyma tissue of twigs. Usually eggs are laid in a lined group at a distance of 0.3-0.5 mm of each other (Mendel et al., 2004;Shylesha, 2008). After hatching, the larva remains in a tissue cavity and its growth and gall development take place simultaneously. Gall development consists of five stages, described in Mendel et al. (2004):
- First stage: at the deposition site, a little spot of dead cells (epidermic and sub-epidermic), similar to a cork tissue, becomes evident, without any initial gall-shaped formation (Jacob and Ramesh, 2009;Kumar et al., 2015). A change in colour from green to pink or reddish usually occurs to the cells of midribs containing the eggs, and the spherical shape of the gall starts to be visible at the end of the stage, usually 1-2 weeks after deposition (Mendel et al., 2004;Jacob and Ramesh, 2009).
- Second stage: in the following days galls reach their maximum size and attain the typical green bump-shape (Jacob and Ramesh, 2009;Kavitha Kumari et al., 2010;Eyidozehi et al., 2014).
- Third stage: galls start to lose their green colour, turning into a glossy reddish colour (ICFR, 2011).
- Fourth stage: galls lose their glossiness, turning into dull pink/dark red (Kavitha Kumari et al., 2010).
- Fifth stage: corresponds to adult emergence, with exit holes visible on the galls surface. Gall colours turn to light brown on the leaf or red-brown on the stems.
Gall formation on leaf petioles, midribs and young twigs usually results in leaf shape deformation. Heavy infestations can firstly cause leaf deformation, due to curling of the midribs, premature aging and leaf fall (Nugnes et al., 2015), and eventually stunted growth of the tree (Mendel et al., 2004;Eyidozehi et al., 2014). Heavy infestation can seriously damage young plantations and nursery seedlings, although tree mortality has not been observed to date (EPPO, 2006).
The majority of Eucalyptus species have been confirmed to be susceptible to L. invasa (Jorge et al., 2016). Among these, E. camaldulensis (var. camaldulensis and obtusa), E. grandis, E. robusta and E. tereticornis showed remarkably high susceptibility to the blue gum chalcid (Mendel et al., 2004;Thu et al., 2009;Nyeko et al., 2010). Studies carried out on several clonal hybrids or clones of these species showed that the incidence of L. invasa infestation could affect them differently (Nyeko et al., 2010;ICFR, 2011). E. gomphocephala and E. occidentalis did not show susceptibility to L. invasa, while E. erythrocorys exhibited “cork tissue” symptoms some days after deposition, but no further gall formation was observed (Mendel et al., 2004).
To date, the only susceptible species not belonging to the Eucalyptus genus is Corymbia polycarpa (Thu et al., 2009), with other species of this genus (C. citriodora, C. maculata, C. torelliana) apparently being tolerant (Mendel et al., 2004).