8/10/10 - Sudden browning of the foliage on the eucalypts along Taroona's ridgetop, the Southern Outlet and Bonnet Hill was first noticed in mid-August 2010. The TEN network did what it does best - we networked! Within a few days, botanists, ecologists, foresters, entomologists and zoologists were on the job and involved in investigations as to the cause. Initially thought to be suffering from drought, it was soon realised that a billion tiny caterpillars had been munching their way through the canopies.
The caterpillar is the larvae of the native painted cup moth (Doritifera sp.). It occurs naturally right across south-eastern Australia. Here in Taroona, it is feeding on our three dominant eucalypt species - Eucalyptus pulchella, E. viminalis and E. globulus - all of which provide habitat for a great host of birds, mammals, and other invertebrates, but importantly, provide food for two of our threatened species - the swift parrot and the forty spotted pardalote.
Since first noticing them a month ago, the caterpillars have doubled in size and are now about 2 cm in length. With very short legs, they look more like slugs than caterpillars. As they mature, their colour changes. Younger caterpillars are jade green, with black stripes, and pink spines - and two anterior 'horns'. Fully mature caterpillars are paler green and lack the pink colouring. They are armed with tufts of spines on the tops of their bodies, which can sting. Little is known about their predators, but their bright colouring, spines and chemical defences probably ward off many predators. As younger caterpillars they were feeding on the leaves by removing the upper epidermis of the leaf, which caused the 'browning off' of the leaves. Now that they are older, they are consuming the entire leaf.
The defoliation of the trees is noticeable from a great distance, with bare branches emerging amongst the dead foliage. Walking amongst the affected Eucalypts, it's extraordinary to see the change in the appearance of the bushland, with the canopy now being so sparse.
With so much dead material (leaf litter and branches) the increased fire risk this season is a real concern. With the last big bushfire in 1967 - and a smaller one in 1998 - it's not a matter of if there is a bushfire, but when. To this end, the Tas Fire Service and local Taroona Fire Brigade have been alerted.
It is unknown how much longer and wider the infestation will spread. It has also been recorded at Lower Snug, and in Taroona it is continuing to spread downslope onto the Alum Cliffs. It doesn't appear to be spreading toward Mt Nelson at this stage.
Eventually, the caterpillars will cease feeding when they pupate in the next few weeks. Studies have shown that there are usually recurrences of outbreaks in subsequent years, but to a lesser extent than the initial outbreak.
Will the eucalypts recover? Despite there being no known incidence of this degree of infestation having occurred in Tasmania, they are expected to recover. This is based on a similar outbreak in East Gippsland in Victoria of Doratifera in 2003 and 2005 (affecting different eucalypt species). Foliage cover returned to a degree between episodes, and the defoliation was less severe in the second episode. See article in the Australian Forestry Journal (http://www.forestry.org.au/ifa/c/c3-ifa.asp?ID=1802)
What has caused the outbreak? The article states: "The cause of the outbreaks by Doratifera spp. is uncertain because of insufficient knowledge concerning their lifecycle. While climatic factors are likely triggers, other factors such as eucalypt host susceptibility, foliage nutritional status, altitude, forest type, soils and geology may also influence the occurrence of Doratifera spp. outbreaks."
As this article above also points out, it should be remembered that this is a native species, in a native forest and part of the normal forest ecosystem.
Watch this space!
(Please contact TEN if you have any new information - or corrections to this article - and we will update accordingly.)
FIRST OF ITS KIND
12/10/10 - Dick Bashford, Forest Entomologist with Forestry Tasmania informed us that there have been smaller isolated outbreaks of Doratifera pinguis in Hobart area before (Lindisfarne 2008, Gordon/Channel this year). He believes the Taroona species is Doratifera oxleyi, which is not a common species in Tasmania, and the Taroona/Bonnet Hill/Southern Outlet etc outbreak is the first record of this species in outbreak in Tasmania.)
REMARKABLE RECOVERY
28/5/11 - Our hilltop Eucs have made a remarkable recovery following severe defoliation last year due to a population explosion of the larvae of the native cup moth (Doratifera sp). The recovery has been so good that it is difficult to see where the outbreak once existed. It will be interesting to see if there are any subsequent outbreaks over the next few years.