The Gum Leaf Skeletoniser

.....Uraba lugens

The Gum Leaf Skeletoniser is better known for the damage it does to Eucalyptus leaves than for the moth itself. At this time of year I find hundreds if not thousands of these caterpillars up the back of our place.

The caterpillars are gregarious and feed on the surface of the leaf, leaving behind just the veins or skeleton as can be seen in photo #6 below. Each time they shed their skin the old head capsule is retained like a little party hat until you end up with 3 or 4 stacked up high.

If disturbed they will all jump overboard and hang from a thread. That's what enabled me to get the shot of the underside in photo #3.

(Click on Photos to Enlarge)

#1 - The Gum Leaf Skeletoniser - Uraba lugens

#2 - The Gum Leaf Skeletoniser - Uraba lugens
Carrying two old head capsules which would suggest it is a third instar larva.

#3 - The Gum Leaf Skeletoniser - Uraba lugens

Defense tactic of dropping from a leaf attached by a thread of silk.

#4 - The Gum Leaf Skeletoniser - Uraba lugens
Gregarious in nature

#5 - The Gum Leaf Skeletoniser - Uraba lugens
Various instars

#6 - Leaf damage caused by the The Gum Leaf Skeletoniser - Uraba lugens

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Caterpillars

Below are a few caterpillar photos from today. This is the first time I've found Hakea Moth larvae - Oenochroma vinaria in the backyard although I certainly see the moths often enough at the light trap.

(Click to Enlarge Photos)

#1- Hakea Moth - Oenochroma vinaria - Defensive posture


#2 - Hakea Moth - Oenochroma vinaria feeding on Hakea decurrens
Note only the cuticle is being eaten.

#3 - Crexa Moth - Genduara punctigera feeding on Exocarpos cupressiformis

#4 - Helena Gum Moth - Opodiphthera helena - 1st (left) and 2nd (right) instars

#5 - Helena Gum Moth - Opodiphthera helena - 2nd instar

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Caterpillar - Helena Gum Moth

You may remember the Helena Gum Moth I posted here recently. If not, then you can see the photos of the moth and it's eggs by clicking here. I have had a dozen or so of these moths in the backyard since then but all have been males except that first one. Fortunately I was able to get some eggs from her.

On the nights of the 19th and 20th October she laid 108 eggs. Most of these hatched 14 days later on the 2nd and 3rd of November. I had hoped to get a shot of them hatching but they seemed to do so overnight. Whether this is normal for them or just coincidence I cannot say. Certainly I've had eggs of many other species which have hatched during the day.

I've been feeding them on Eucalyptus pauciflora which is not a local species. At this stage they have shown a strong preference for young leaves.

The last time I tried to rear these I only got them to second instar before they succumbed to a fungal attack. This time I've put them in a larger rearing cage with better ventilation so hopefully I'll be successful this time round.

(Click on Photo to Enlarge)

Helena Gum Moth - Opodiphthera helena - 1st instar larvae

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Not Just a Twig

...but a home for Hemibella heliotricha

More than just a twig, the photos below show the larval case of Hemibella heliotricha, a moth of the very large family Oecophoridae. There are other members of the genus on the mainland. I noticed many of these larvae last August on one particular tree. I've been watching closely for the last few weeks and finally spotted one on the same tree today.

The larvae of the Genus hollow out twigs to make a larval case in which they gain protection. I'm always impressed by the straightness off the cross cut and the neatness of the round hole. They feed on Eucalyptus leaves. You can see the holes in the leaf where it has been feeding. Other parts of the leaf have only had the surface grazed. The caterpillar will use successively larger twigs eventually pupating within.

They can attach the twig to a leaf or branch using silk. Using a twig also offers pretty good camouflage but their habit of attaching themselves at right angles to a surface makes them a little easier to spot once you know what you're looking for.

(Click photos for larger versions)

Larval case of Hemibella heliotricha - 17mm long

Larval case of Hemibella heliotricha - Showing the hole at one end.
The twig is 2.2mm in diameter

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Caterpillar - White Tussock Moth

Oh ... and you all thought I would do another bird post :-)

I noticed a couple of these caterpillars in the garden today. They are the larvae of the White Tussock moth Acyphas semiochrea. They were well exposed on the outer leaves of a Black Wattle - Acacia decurrens. This wattle is not native to Tasmania and the local foodplant would normally be the Silver Wattle - A. mearnsii. This moth species is not confined to Tasmania. It is found in many areas of Australia and feeds on various Acacia species. The hairs on the caterpillar are also known to cause skin irritations.

The caterpillars feed at night and rest on the foodplant during the day. The two I seen today were so well exposed that I would imagine they stand a good chance of being killed by birds or parasites. If not, then in time they will make a white papery cocoon in which to pupate and will be on the wing from spring through to autumn. You can see the imago by clicking here.

Note: I will probably be out of action for little while. Will be back to blogging soon enough :-)

Acyphas semiochrea
Notice the two forward pointing tufts of hair at the head.

Acyphas semiochrea

Acyphas semiochrea

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A Closer Look at the Caterpillar

After my Fungivorous Caterpillar post yesterday, Tim Eisele asked a very good question as to whether I had seen prolegs. The lack of prolegs may have suggested a beetle larva. My initial ID yesterday was based only on the shape of the head capsule and the large amount of silk webbing. There are some Coleoptera with silk glands although I'm not aware of any which make such a large amount of webbing over there food source. If anyone is aware of such a beastie please let me know. In any case I needed to get a closer view.

The following shots were taken with my macro lens under better lighting than yesterdays. The first image shows a series of prolegs. There are at least 6 pairs visible plus the anal claspers which makes 7. There may also be another pair just out of view one segment closer to the head. The prolegs are not well developed.

Caterpillars generally have 5 pairs of prolegs although some have less and some, such as those of the family Micropterigidae, can have 8 pairs of prolegs. The presence of prolegs does not in itself prove that the larva is Lepidopteran. The larvae of some other orders can also have prolegs. The one sure way to identify it as a caterpillar is to look for crochets - hook-like spines that form a ring around the prolegs. For this I dragged out my el cheapo microscope. The problem with the microscope is that it lacks depth of field. I really need to get myself a proper binocular, disecting microscope. I did eventually manage to focus on a single proleg and found it did indeed have crochets. So I can now say for sure that this is a caterpillar. I would love to have photographed this but the microscope camera did not come with a driver for Linux.

I could not find any true legs. There are some caterpillars which have reduced or absent true legs. The second photo does show what may be one leg making an appearance. You can be the judge of that.

Not the best photo but you can make out the reduced prolegs

Is that a "true leg" sticking out from below the thorax?

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Fungivorous Caterpillar

I photographed some fungi in the backyard today. It's one of the more common species on our hill.

Laccaria sp. (as idntified by Sarah in the comments below)

Having read Denis Wilson's blog entry where he found a small fungivorous creature living between the fungal gills, I thought I had better have a closer look. Sure enough there were signs of something living there. Some parts of the fungus had been eaten and there was a network of fine webbing over the gills.

Fine webbing between the gills

Closer examination found the culprit - a small caterpillar which I measured at just 3mm in length. I have tried to get a better shot but the caterpillar has since crawled off and hidden somewhere within the fungus. I will attempt rearing it but I'm not too sure on my chance of success. If I manage a better photo at some stage I'll update this entry.

White hairless caterpillar with dark head capsule

An update to this post can be found here.

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Parasites of Caterpillars

Population Control

Given that some moths can lay many thousands of eggs, we can be glad that there are many ways by which the lepidopteran population is regulated. Predation by birds and small carnivorous mammals have a major impact on numbers.

In a healthy eucalypt woodland, birds can take about half of the insects produced (some 30 kilograms per hectare per year) and small mammals (bats, sugar gliders, and so on), predatory insects and spiders take a substantial proportion of the rest.

Salt, Lindenmayer, & Hobbs - (2004)

Aside from predators, there are also things like fungal and bacterial attack to contend with. One well known bacterium, Bacillus thuringiensis, marketed under names like Dipel, is regularly used by gardeners to control caterpillars.

Anyone who has had a go at rearing caterpillars, will also be well aware of the many parasites of caterpillars such as mites, wasps, and flies. While it can be disappointing for a rearing project to have been parisitised, it is also quite fascinating to get a close up view of these natural population controls in action. Below is a brief look at a few of the parasites I've come across.

Mites

Erythraeid mites are the most common ectoparasites of moths and their larvae. (Ectoparasites are those which feed externally on there host.) These do not kill their host. The six legged mite larvae gorge themselves on the blood of their host. When finished feeding they drop off in order to complete their development into the eight legged adult stage.

The photos below shows red Erythraeid mites on Uraba lugens (Gum leaf skeletoniser).

While your there, have a look at the little hats the Gum leaf skeletoniser wears. Each time they shed their skin, a bit of the dried skin and the old head capsules do not detach and so they pile up like little hats.


Parasitoids

Unlike ordinary parasites, Parasitoids eventually kill their host. They feed on the less vital organs at first. Common parasitoids of Lepidoptera include Ichneumon wasps, Braconid wasps and Tachinid flies.


Ichneumon Wasps

Ichneumonidae is a very large family of parasitic wasps with around 2000 species in Australia and about 120 of these found in Tasmania. They attack not only several insect orders but also spiders.

Pupation can take place either within the host or it may exit the host first and make it's own cocoon on vegetation or among the leaf litter. The next shot shows an exit hole where dozens of small Ichneumon wasps have emerged from the pupa of Pieris brassicae (Large White Butterfly) These ones have emerged as adults having pupated within the butterfly pupa. (Note: The 4 photos relating to Ichneuman wasps were taken in Scotland)

With larger species of wasp there may be just one egg laid in each caterpillar. For example, here is an arctiid pupa which had a single large Ichneumon wasp emerge from it.

Braconid Wasps

Another major family of parasitic wasps are the Braconidae. They belong to the same superfamily, Ichneumonoidea, as the Ichneumonidae. Australian has about 800 species of Braconid wasp and at least 52 of these are found in Tasmania.

Braconids parisitise insects from many different orders including the Lepidoptera. The female generally lays eggs in the host larvae although sometime they are laid in the host insects eggs. In rare case adult hosts are attacked. Braconids are usually internal parasitoids (Endoparasitic) although some feed externally (Ectoparasitic).

Some Braconids will pupate within their host although more generally the larval grubs will exit their host first. Below is a photo of some Braconid wasp pupae. They had eaten there way out of the caterpillar and immediately made their silk cocoons.

Braconid pupae shortly after exiting an Arctiid caterpillar

Tachinid Flies

There are over 540 species of Tachinid fly in Australia with around 125 of these found in Tasmania. The larvae of these flies are parasitoids of other insects from several insect orders including Odonata, Hemiptera, Coleoptera and especially the Lepidoptera.

The flies generally lay there eggs on, and sometimes in their host. Others will lay the eggs on plants where the will either be ingested by the host or else hatch first and then find their way onto their host. The photos below show two, of three flies along with an empty puparium. These came from an Arctiid caterpillar. In this case the fly larvae, each only 4mm in length, exited the caterpillar prior to pupating leaving behind the shriveled body of the caterpillar.

An Arctiid caterpillar after being parisitised by Tachinid flies

The Tachinid flies and a pupal case

References:

Common I.F.B - (1990) - Moths of Australia - Melbourne University Press

CSIRO - (1991) The Insects of Australia - A Textbook for Students and Research Workers; Volume 1 & 2; Melbourne University Press; Carlton; Australia

Salt, Lindenmayer, & Hobbs - (2004) - Trees and Biodiversity - A Guide For Australian Forestry

Semmens, McQuillan, Hayhurst - (1992) - Catalogue of the Insects of Tasmania -

Zborowski & Storey - (2003) - A Field Guid to the Insects of Australia

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