Australian insects

These insects are often called Physapoda in allusion to their bladder-shaped feet; but though some are wingless, the name Thysanoptera seems much more suitable, for all the typical forms have both pairs of wings beautifully fringed with hair-like filaments, hence the name “fringe-wings.”

Thrips have few affinities with any of the other orders, and their exact position in any system of classification has puzzled most entomologists. The remarkable structure of the mouth, which has been studied by Messrs. Jordan and Garman, appears to consist of a compound of biting jaws and a sucking style. Uzel has figured it in his “Monographie der Ordnung Thysanoptera” 1905, but the exact manner in which they take their food is not yet clearly understood. The integument is very thick and opaque, and the head comes to a cone-shaped point at the mouth adjacent, to the ventral surface of the sternum, so that the complicated structure of the mouth is difficult to study. The eggs are laid upon the food plant, and the young undergoing a series of moults resemble the adult in general form, and the distinction between the larval and pupal forms, though noticeable, is very slight.

The members of this Order sometimes appear in immense swarms and do a great amount of damage to cultivated plants and field crops. They are widely distributed over the world, and many species are cosmopolitan, having been spread with the introduction of their food plants. The group is well represented in Australia by many remarkable and striking species, some of which form distinct galls. This Order contains the single family Thripidae.

Family 1. Thrips.
THRIPIDAE.

These are elongate, black, or brown, with 6 to 9 jointed antennae standing out in front of the head; large eyes; with ocelli (usually absent in the wingless forms). The elongate head comes to a cone-shaped point at the extremity; the mouth consists of a pair of jaws with a pointed style between them. The thorax, as broad or slightly broader than the body, is elongate, and furnished in the typical forms with two pairs of delicate oar-shaped wings with a simple medium parallel vein in the centre of each fore wing, and both pairs fringed with delicate feather-like filaments; both pairs are attached at the base to the dorsal surface of the thorax, and when at rest are folded down the centre of the back. The legs are short and simple, but sometimes the thighs of the front pair are thickened; the tarsi consist of two short simple joints, the last bladder-shaped. The abdomen is slender and is rounded at the extremity, and in one division ends in a slender tubular process. Most of them are minute creatures; the giant among them comes from Australia, but this only measures ½ an inch in length. Though most species are vegetarian in their habits, feeding upon the surface of plants or the pollen of flowers, a few are said to devour mites and other tiny creatures.

Plate XXXVII.—THYSANOPTERA.

Family Thripidae.

In Uzel’s Monograph only 135 species are catalogued, half of which are European. Haliday (Entomological Magazine 1836) divided all the known species into two groups or sub-families, viz.: Terebrantia, in which the females have an external toothed ovipositor (including all the typical European forms); and the Tubulifera, in which the ovipositor is hidden and the tip of the abdomen is produced into an elongated tubular process (most of our indigenous species fall into this latter group).

Heliothrips haemorrphoidalis, an introduced species, is our commonest thrips, and is world-wide in its range. It measures about ¹⁄₁₆ of an inch in length, is stout in proportion; has the head and thorax rugose, and is of a uniform black tint with very light-coloured wings. It not only infests and damages a great number of garden plants, but is spreading to our native bushes, for I have taken them on young eucalypts far away from any gardens. The Giant Thrips, Idolothrips spectrum, was described by Haliday from specimens collected by Charles Darwin in 1836; he described the sexes as different species; and a smaller dark variety was given a third specific name. It is a very common insect in Eastern N.S.W., hiding among the foliage of dead eucalypts; when disturbed it runs about with its wings and elongated body turned upward in the manner of a small “rove beetle.” It has an extended range from Tasmania to Southern Queensland. I recorded its life-history (Pro. Linn. Soc. N.S.W. 1904), where the different stages of development are figured. Its large size, long antennae, elongated neck-like prothorax, and red spined abdominal segments and tubular appendage are very distinctive characters.

The most remarkable Thripidae however are those that infest many of our forest shrubs, such as Acacia, Hakea, Callistemon, and other scrub trees in Central Australia. These live in galls which they produce by puncturing the edges of the young leaves and causing them to curl over; or by attacking the leaf buds and aborting the tips of the twigs into irregular masses of thin woody galls; or again, the leaf is pierced from the under side by the female thrips, causing the leaf to blister on the upper surface, which gradually expands into an oval or rounded gall as large as a small marble, and into which most of the leaf is often absorbed, leaving only the leaf stalk and the tip, which forms a short tail curving up from the basal scar. Many of these galls are closely packed with small semitransparent larvae and pupae in all stages of development, the offspring of the single female thrips that first caused the gall. Noting this remarkable habit of Australian thrips, so different from that of all other known species, I forwarded specimens and galls to Dr. Sharp, who notes the fact in the Cambridge Nat. Hist.: Insects. It seems apparently to be a case of the survival of the fittest, for in the dry intense summer heat of the interior these delicate insects could not live on the outer surface of the foliage, while, enclosed in these galls, they can survive the hottest and driest season. Species of gall-making thrips have been recorded recently from Java. Uzel described one of these gall-making species, Phloeothrips tepperi (Acta Societatis Entomologicae Bohemiae 1905) from specimens obtained in S. Australia by Tepper, and which form oval galls upon the “Mulga,” Acacia aneura. This species is also common in the western parts of N.S. Wales upon the same tree, which also bears two other distinct thrips galls.

I have figured a remarkable rugose gall, obtained near Tamworth, N.S. Wales, upon a short-leaved acacia (Agricultural Gazette N.S.W. 1906); the maker of this gall will not fit into any known genus, and therefore I propose for it the name of Kladothrips rugosus. It has an elongate rounded head, with the thighs of the fore-legs greatly thickened and the apex of the tibia produced into two blunt claws.