Friday 7 November 2014

Two new species of Ironwood infesting Gall Wasps from Micronesia and Australia.

Ironwood Trees of the genus Casuarina are native to Australia, Southeast Asia, South America and the islands of the western Pacific. They are widely grown for their timber, as well as for windbreaks and for their ability to stabilize soils in erosion-prone areas. However in some places where they have been introduced they are considered to be invasive pests, which outcompete native plants and modify their environment in unwanted ways. Thus any pest or pathogen species which affects Ironwoods is of interest, both due to the harm it can cause to a valuable commercial species, and for its potential to act as a biological control on a harmful invasive one.

In a paper published in the journal Zootaxa on 23 April 2014, NicoleFisher of the Australian National Insect Collection at CSIRO Ecosystem Sciences, Aubrey Moore of the Western Pacific Tropical Research Center of the Universityof Guam, Bradley Brown and Matthew Purcell of the Australian BiologicalControl Laboratory at CSIRO Ecosystem Sciences, Gary Taylor of the AustralianCentre for Evolutionary Biology and Biodiversity and School of Earth andEnvironmental Sciences at The University of Adelaide and John La Salle of the Australian National Insect Collection and Atlas of Living Australia at CSIRO Ecosystem Sciences describe two species of Gall Wasps infesting Ironwood Trees from Micronesia and Australia. Both are placed in the genus Selitrichodes.

The first new species is named Selitrichodes casuarinae, which derives from Casuarina. The species was discovered in Guam, where Ironwoods are widely planted as windbreaks, shade trees and erosion controls, but where they have begun to decline and die. Selitrichodes casuarinae has subsequently also been discovered on Rota and Palau, however it is presumed to be native to Australia, as this is the source of the Ironwood trees grown on these islands; the Australian distribution of the Wasp is unknown.

Adult Selitrichodes casuarinaeon Causarina stem. Aubrey Moore in Fisher et al. (2014).

Selitrichodes casuarinae is a small yellow and brown Wasp. The males reach 0.75-1.25 mm in length, the females are slightly smaller, reaching 0.70-1.20 mm. The Wasps cause galls (tumourus growths in which the eggs are laid and where the larval Wasps grow) on the tips of branchlets of Casuarinae quisetifolia. The branchets with galls are notably stunted and have a dry biomass reduced by about 35%.

Stunting caused by Selitrichodes casuarinae. Aubrey Moore in Fisher et al. (2014).

The second new species is named Selitrichodes utilis, meaning useful or beneficial; the species is being investigated for use as a biological control in parts of North America where Ironwoods are considered an invasive pest. It has been found in Queensland and New South Wales, though to date all specimens collected have been females.

Selitrichodes utilis, female specimen in lateral view. Nicole Fisher in Fisher et al. (2014).

Selitrichode sutilis is dark brown or metallic green in colour and reaches 0.85-1.55 mm in length. It forms galls on the stem tips of Casuarina glauca.

Leaf bulbgalls on colony plant, Casuarina glauca. Bradley Brown in Fisher et al. (2014).

See also…

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