Are local Eucalypts dying?

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Major defoliation of Eucalypts are linked with the cup moth caterpillar. It's behaviour is described and Dr Paul Horne, a Melbourne Entomologist, explains the "Predator – Prey Cycle" as a natural means of control.

Many Eucalypts in the area appear to be dying.  Young Eucalypts are being destroyed. They are defoliated and looking brown and dead, with even the outer bark being destroyed; mature trees appear to be dying because of their many brown leaves.   Bellbrae properties are suffering and the problem is evident in Eucalypts all along Vickerys Road.  The impact can also be seen along the Great Ocean Road, especially around Anglesea and Aireys Inlet and is likely to be much more widely spread.

Who has some knowledge that can help?
Paul Horne, a Melbourne based Entomologist, known for his work on Integrated Pest Management, was contacted for information and advice.  He responded promptly, identifying the culprits.

What's happening?
Over the past month or so,  there's been an infestation of a caterpillar, about 15mm long, which pupates and becomes what is known as a 'cup moth' (Limacodidae).  There are several species from the genus Doratifera and they're all very colourful. 'The name comes from the hard pupal cacoon, the top of which is sliced off like a boiled egg when the adult moth emerges' (Horne & Crawford 1996, Backyard Insects, Melbourne University Press).

Can I take a closer look?
Do take a look at the caterpillars as the colours are both beautiful and varied but there is a strong defence system, so be wary of the clusters of tiny stinging spines that emerge from the caterpillar - at both ends - when it feels threatened.  The spines appear in pretty yellow rosettes and the sting is painful if the spines are broken and poison released.  The caterpillar has an adaptive defence so you may observe that the spines are retracted when not needed.  You may also notice that viewed from above, you can't see the caterpillars' legs. Their legs are shorter than most caterpillars; and if you look at their underside through a glass jar, you will see their paired legs in action, with the caterpillar appearing to glide along on its yellow underbelly, rather than walk.

Is there a solution for the wider environment?
Amongst the sample of caterpillars collected this month, some were diseased and died soon after collection.  There's also evidence of a parasitic wasp, a natural predator, where the wasp lays her eggs within the body of the caterpillar, killing the caterpillar with the emergence of young wasps.  The bonus is that young wasps emerge, to become parasites of still more caterpillars. What becomes evident here, is what Paul Horne calls, the "Predator – Prey Cycle": 'if conditions favour pests then they will boom, and only subsequent to that will beneficial insects etc respond.  So mature trees should be able to survive the lag-time between the arrival of the pest and the arrival and build-up of the beneficial species. However, young plants may not survive'.

What if the cup moth caterpillar has moved from the Eucalypts to my fruit trees?
If it has moved from the Eucalypts to your fruit trees or exotic plants in your house garden, there is something you can do.  Buy some Dipel from your local nursery.  This will be a powder which you mix with water and spray on the caterpillars: spray after 3pm and when there's no immediate prospect of rain.  Just spraying the plant doesn't work, however, as the caterpillar has to eat the bacteria that's present in the sprayed mixture.  If you do decide  to buy some Dipel, be sure to check the 'use by date' as bacteria won't survive very long.  Paul Horne adds: 'the decision on what product to use on young or older plants is critical.  A cheap broad-spectrum insecticide will kill all beneficials (e.g. the parasitic wasp) while giving a short respite to pest damage (e.g. from the cup moth).  That is why Dipel is a better product to solve the problem if you decide to spray.  It will control the pest but not disrupt beneficial species'.