Xyloryctine Moths of Australia
Genera and Species
An unidentified Xyloryctine larval habitus on Acacia aulacocarpa. The larva tunnel goes down the branch, below the opening which is sealed with silk to which frass, feculae and Acacia phyllodes are attached. The larva feeds on the phyllodes, which it gathers by night, as they dry out.
The Xyloryctinae are a subfamily of Gelechioid moths which were first identified by the habits of some of their larvae, which make residential tunnels in wood, collecting leaves by night which they secure with silk to the entrance of the burrow, feeding on them as they dry out. Although most feed on leaves collected in this way, some feed on bark, cambium, or lichens. Internationally, Xyloryctines are pests of commercial tree-grown crops, including tea, coffee, cocoa, coconut, and macadamia. One Australian species, Maroga melanostigma, has crossed over from its nativeAcacia host and has become a pest of stone fruits.
These moths are morphologically distinguished by their tergal abdominal spines, and the lateral fusion of their uncus and gnathos in the male genitalia. Like other Gelechioids they have a scaled haustellum, and they share the lack of an antennal pecten with some Oecophorid species. A rule of thumb current among collectors is that the hindwings of some species, especially the smaller ones, are trapezoidal in shape,and have a defined anal angle between the termen and the hindmargin. Many genera and species are endemic to Australia, where they attain relatively gigantic size compared to their tiny micromoth relatives.
Many Xyloryctines readily come to ultraviolet and other forms of artificial light; those that do not have to be discovered as larvae or pupae and raised in their burrows. As many larvae inhabit high treetop branches, collecting them is not always easy. In the following transcript, the Queensland naturalist Rowland Illidge describes his method of rearing them from larvae or pupae.
XYLORYCTS , OR TIMBER MOTHS.
(Read on 15th December, 1892).
The moths of the family Xyloryctidae were known to me many years ago , and the curious habits of the larvae formed the subject of frequent investigations, but not until the present year did I prosecute any active search for them. This season I have been eminently successful, as the exhibit illustrating these remarks will prove. Many of you I have no doubt have noticed those strange webs mixed with dejectamenta, little bits of bark, and woody matter, which serve to hide the entrance to their burrows or tunnels in the stems and branches of young trees. The caterpillars form these tunnels and so cover them, I believe, to protect themselves from external foes, such as birds (they are certainly not protection against the ichneumonidae, for these insects destroy them wholesale), for being fat, naked grubs with only a few slight hairs, they no doubt would form a delicious morsel. In support of this latter opinion we have the fact that the aboriginals in former days sought out these larvae, cut them out of their holes, and ate them on the spot, as we would an oyster.
These caterpillars are all nocturnal in their habits, and, as far as my researches show, only leave their chamber in the stem during the nighttime, when they hurriedly bite off a leaf and retire bearing it off with them. It is fit curious sight to watch them dragging off the leaf and entering the hole backwards (which they do with considerable celerity if at all disturbed), raising at the same time the covering which conceals the entrance to their burrow with their hinder extremity, and pulling the leaf after them. The leaf is now secured with a few silken threads, and the insect feeds on it at its leisure without fear of being snapped up by some outside enemy.
Some of the species, however, do not appear to feed on the leaves, but devour the soft bark round the entrances to their burrows, spinning the web-covering for some distance, and indeed extending it as they exhaust the food supply in the immediate neighhourhood of the hole. There is one species at present known which makes no burrow or tunnel, but simply spins its covering on the tree stem and feeds on the soft bark underneath, and when changing to the pupa state forms a cocoon of silk and bits of bark and excrementitious matter mixed. Others again spin long silken galleries amongst the leaves and twigs whilst many tunnel into the cones and seed-heads of plants and trees. Mr. Meyrick states that T. laetiorella resides in a barricaded tunnel in stems of eucalyptus, etc.; whereas I find it to be a bark-feeder and that it spins a cocoon. I have reared many and have never found them as stated by him, though it is not unlikely that his statement is correct, for I know Xylorycta luteotactella occasionally to reside in a tunnel in stems of Banksia integrifolia, though usually spinning galleries amongst twigs and leaves, and finally forming a cocoon.
The larger and more characteristic species of the family are all, however, tunnel-makers. As the larvae grow bigger they extend the tunnel in size, and this seems to form the chief impediment to rearing them from a young state, as the wood dries up when cut off and becomes too hard for their mandibles, hence they either die in the tunnel or leave it. I have several times succeeded in getting them to form a silken chamber along the interior angle of the box in which they have been placed and so reared them without affecting the normal size of the imago. It is therefore necessary for success in securing the perfect insects to obtain their caterpillars when full-fed or nearly so or else when they have already passed to the chrysalis state.
They seal themselves in the burrow when about to change, and some of them do this very artfully. One or two species spin out a spout-like web of silk and bits of bark mixed, which looks like a little piece of dead or decaying stick; another species spins a web flush with the bark and so exactly like it that it is almost impossible for it to be distinguished. Others again simply spin a strong web inside and across the opening of the tunnel, whilst some content themselves with only partially closing the hole with a curved piece of brown horn-like substance, the nature of which is unknown to me, and occasionally the opening is quite unprotected. Just before pupation takes place the external covering is usually torn away, and a very careful search is then necessary to secure examples. They remain in the pupa state for a very variable period, some emerging in a fortnight or three weeks and others after as many months. As a rule the trees are not seriously damaged by their burrows, though odd branches become sickly and die. The large Maroga unipunctana, however, is an exception, for it feeds on the bark and frequently eats completely round the stem, thus ringbarking the tree. Dogwood and wattle trees may often be found quite dead above from this cause. On the moth emerging the hole soon commences to close up and no external trace of it is left after a little time, except perhaps a slight scar which also in course of time disappears. The abovementioned M. unipunctana is said to be very destructive in Victoria to fruit trees, but I have not noticed its appearance here in such trees, possibly because my experience is limited to my own garden. I have, however, noted a large species amongst leguminous trees in the Botanic Gardens, one of which, in front of the curator's house, has been utterly destroyed by them. The pupae of the species of Xyloryctidae are usually cylindrical, conical at the hinder extremity and rather flattened towards the head, with one notable exception. In the insect affording it the chrysalis has a strange bifurcated projection in front, which appears to be for the purpose of cutting, auger-like, a way through the very thick and strong web the larva spins in front of its tunnel before changing to the chrysalis. Though many of the insects are quite common in the larval state, yet the moths are of great rarity and are seldom seen even by experienced entomologists. Securely as they appear to be hidden in these tunnels, yet they have enemies in various ichneumons with long ovipositors, which find them out and deposit their eggs in their bodies thus fortunately preventing them from becoming too plentiful. The larva of a beetle belonging to the Cleridae, Natalis sp., also preys upon them, and finally changes to the perfect state in the gallery lately occupied by the caterpillar of the Xyloryct moth.
Protective resemblance has evidently much to do with the explanation of the different colours and patterns displayed by many of the moths. For example the close similarity in colour between Uzucha humeralis and the bark of the spotted gum and between Cryptophaga nubila and that of the teatree is very obvious, and becomes significant when we remember that the trees mentioned are the food plants of these moths. At the same time other Xyloryctidae, e.g., C. epadelpha, seem to be coloured In a manner specially suitable for rendering them conspicuous.
R. Illidge, 1895: Xylorycts, or timber moths. Queensland Nat. Hist. Soc. Trans., 1, 29-34.