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Volume 21, 1888
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Art. XXX.—On some Gall-producing Insects in New Zealand.

[Read before the Wellington Philosophical Society, 17th November, 1888.]

Plates XI. and XII.

A Common plant in gardens in this country is a native shrub—Olearia furfuracea—usually known to settlers by the name of aké-aké, though the true Maori name is aké-piro. It is a somewhat straggling bush with light-green leaves, the under sides of which are whitish; the leaves much “crimped.” The flowers are small, yellowish, appearing in autumn, and have a faint scent resembling that of the lilac. The plant has no particular pretensions to beauty, but it grows fast to some ten or twelve feet in height, and is useful enough as shelter in a garden.

This Olearia is much subject to the attacks of a couple of minute insects, which, though they belong to two quite

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different families of the class Insecta, the Hymenoptera, and the Diptera, seem to have made common cause against the plant, and live in close alliance at its expense. A good deal of the straggling nature and ungraceful appearance of the shrub is due to their attacks, and doubtless if one could insure freedom from them the Olearia, might be made much more ornamental than it is. Of these two insects, one, the hymenopter, preys apparently only on the buds and young shoots; the other infests both buds and leaves.

The “galls” produced on the plant are of two kinds. The one affecting the young shoots and buds has the appearance of large excrescences formed round the axils of the twigs, as if in those spots an abnormally large number of shoots had begun to grow out, and, having their growth suddenly arrested, had coalesced in an irregular mass, their stunted leaves crushed up and crowded together. Examples of these are shown in Plate XI., fig. 1, and Plate XII., fig. 1. It will be observed that there is a slight difference between these two, the leaflets in one being much smaller and more crowded than in the other. My experience has been that in the larger one (Plate XII.) only the dipterous insect lives; in the smaller one (Plate XI.) mostly the hymenopterous, but frequently, together with it, the dipteron also. A section of either of these galls will show (as in Plate XI., fig.2) a colony of insects, in the pupa or in the larva stages, living in cells within it. The differences between the two insects may be easily seen by the larger size of the dipteron and therefore of its cell, independently of the differences of colour given below.

The other kind of gall is exclusively the work of the dipteron, and takes the form of blisters on the leaves, as shown in Plate XII., fig. 1, and in section, fig. 1a. When the perfect insect is ready to emerge it breaks a hole through the leaf, and the pupa thrusts itself out for about half its length before the fly emerges, as shown in the figure.

Of these two galls the last, on the leaves, would not probably be hurtful; the other, which arrests and deforms the growth of the young shoots, must exercise a baneful effect upon the vigour of the plant.

The two insects appear to go through their transformations and perform their work at the same periods of the year. The eggs are laid about October, and the larvæ emerge from them in a week or ten days. The larvæ seem to change to pupæ at different intervals—sometimes in early summer, sometimes not until the following spring. The perfect flies emerge about October, and probably, on any particular shrub, all about the same time. Procreation takes place immediately. I have seen a male and a female emerge from a gall almost at the same moment, and five minutes afterwards copulate.

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The following descriptions of these insects are offered:—

Order. Hymenoptera.
Sub-order. Terebrantia.
Family. Chalcididæ
Genus Eurytoma.

Eurytoma oleariæ (Gall-fly of Ake-piro). Plate XI., figs. 116.

Insects inhabiting in the larval and pupal states, in colonies, excrescences and abnormal growths (galls) (figs. 1, 2) on the twigs of Olearia furfuracea. The galls are probably not produced by themselves, but by a dipterous insect. (See below.)

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Larva (fig. 3) about 1/18in. in length, grub-like, fleshy, yellowish; no true legs, but a number of very obscure tubercles; the head (fig. 4) exhibits a convoluted ring with two conical processes within it. On each joint of the body there are two minute circular spiracles (fig. 4).

Pupa (fig. 5) black, exhibiting the immature organs of the imago. The pupa is enclosed in a hard, grey case (fig. 5a), which has all the appearance of the dried larval skin. As coarctate pupæ are not, seemingly, found amongst the Hymenoptera, this case must be taken as an exceedingly closely-woven hard cocoon.

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The perfect fly (fig. 6) is about 1/14in. long; colour black, covered with short, fine, grey hairs; antennæ black; legs yellow; wings dark-grey. The head is transverse; eyes large; palpi short; thorax thick; mesothorax large and somewhat elevated; scutellum small. Abdomen (fig. 13) apparently composed of three parts—a short peduncle, a median cylindrical portion, and an oval hinder region with six or seven segments. The ovipositor of the female and the penis of the male are not usually exserted. Antennæ of both sexes (fig. 7, female; fig. 8, male) with twelve joints, of which the first two are very short, the third much the longest, the remaining nine sub-equal, each slightly dilated at the tip; all the joints except the two first hairy. The antennæ of both sexes are very similar: that of the female may be distinguished, perhaps, by being proportionately shorter than that of the male, and the joints after the third rounder. Feet (fig. 9) slender; the femur only moderately thick; the tibia dilated at the tip and bearing a spur; tarsus of five joints. The spur of the tibia on the two front legs (fig. 10) is peculiarly large, apparently cleft in the middle, with serrated edges; and the first joint of the tarsus has a distinct comb of stiff bristles on its inner side. The spur on the tibiæ of the other pairs of legs is a simple spine (fig. 11), and the tarsus bears no comb. Forewings (fig. 12) hairy, with very few veins; the sub-costal and anal

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diverge almost at once, and extend a little within the margins for about half the length of the wing; at rather more than half their own length a conspicuous cross-vein unites them, and forms thus a triangular basal cell. The hind-wing has only one vein on the surface, the sub-costal extending for half its length and terminating at the two hooks on the edge. Both wings have faint patches of dark-grey on the surface. The exserted female ovipositor (fig. 14) has a somewhat thick cylindrical base, with a long, slender, curved tube, ending in a slightly-dilated bulb with three or four spines. The penis of the male (fig. 15) is long, cylindrical, with an oval terminal bulb, at the base of which is a ring of spines. The spermatozoa, (fig. 16) are about 1/6000in. long; they are wonderfully agile in their motions, and in the specimens observed retained their vitality for more than half an hour after extraction from the male insect.

This insect has been placed here in the genus Eurytoma of the family Chalcididæ, as it seems to agree better with that than any other, although not entirely satisfying the conditions. The veining of the wings appears to be more like that of some Cynipidæ, especially in the triangular basal cell; but the simple form of the abdomen removes it from that family, and the presence of the distinct segment between the peduncle and the true abdominal region approaches somewhat to the Ichneumonidæ. Eurytama and its allied genera seem, indeed, to hold an intermediate position between the two families, and on this account the present insect has been assigned to that genus.

A point of importance remains to be considered. The Chalcididæ are not usually phytophagous, gall-producing insects, but parasitic on other flies; and it has always been a matter of doubt whether any of them depart from the rule. A species of Eurytoma is found to do much damage to wheat in America, producing on the stems galls which weaken and destroy the plant; yet it is not certain whether this fly (Eurytoma hordei) may perhaps not be only parasitic on a larva of Cecidomyia, and that this last larva may not be the real gall-producer. In the present case the galls of Olearia contain, as above stated, dipterous flies (described below), and these are Cecidomyia. Our Eurytoma may thus be merely a “messmate,” to use Van Beneden's term, the dipteron being the real plant-enemy. That it is not a true “parasite” seems certain, as, although its larvæ and pupæ are found mixed indiscriminately with those of the Cecidomyia, they are in separate cells, and the Diptera in the leaf-blisters are never infested by them. On the whole, I incline to the belief that the Cecidomyia produces the galls on the twigs, and the Eurytoma takes advantage of them as a residence.

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Order. Diptera.
Sub-Order. Ovipara.
Family. Cecidomyidæ
Genus Cecidomyia.

Cecidomyia olearæ (Blister-fly of Ake-piro). Plate XII., figs. 113.

Insects inhabiting, in colonies, excrescences produced by the larvæ on the young shoots of Olearia furfuracea; or, singly, blisters produced by the larvæ in the leaves of the same plant (figs. 1, 1a, 1b).

The eggs (figs. 2, 3) are elongated, pointed, red in colour, laid in bundles on the young shoots, usually in or near an axil.

Larva (fig. 4) white, becoming yellow before transformation; elongated, sluglike, footless; the head (fig. 5) has a simple flattish front with two curved claw-like processes, and two others, conical (perhaps rudimentary antennæ). There are only two spiracles, simple orifices, placed on the last segment of the body.

Pupa (fig. 6) naked; head-region black, abdomen red with blackish bands; immature wings and feet noticeable. On the head are four or five shortish bristles.

The perfect fly (fig. 7) is elongated and slender; head and thorax dark-red with large black patches; abdomen dark-red with black spots; legs dark-brown. The whole body and legs are covered with short hairs and with a number of black scales (fig. 13), pedunculate, something like those of Lepidoptera; these scales give the appearance of black bands to the abdomen—they are exceedingly-loose, and apt to fall off at the least touch. The head is transverse; eyes conspicuous, almost covering the head; palpi long, four- (or five-?) jointed. Antennæ (fig. 11) in both sexes of fourteen joints, of which the first two are very short, the rest ovate and sub-equal, with hairs on each; in the female the last twelve joints are separated by short peduncles, which are not apparent in the male. Legs very long and slender (figs. 7, .12); the tarsi, five-jointed, the first joint being very small. Wings (fig. 10) grey, with many short hairs on the surface and a fringe of long hairs on the edge; veins few and not anastomosed; the costal vein extends to the tip and meets the second longitudinal, the subcostal extending to about two-thirds of the length of the wing; the third longitudinal reaches the posterior margin at about half its length, and sends off a branch which extends nearly to the margin between it and the second longitudinal, Haltere (fig. 10) conspicuously long, with a large head. Abdomen of female ending in several short lobes, slightly turned

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upwards (fig. 7); at rest, these are folded together (fig. 8); when opened (fig. 8a) two are long, cornute with sharp ends, and four others, shorter and tubercular, enclose a short cylindrical ovipositor. Abdomen of male ending (fig. 9) in two lobes; when exserted (fig. 9a) the penis is thick, cylindrical, somewhat dilated at the tip.

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Length of the body about 1/9in.; length of legs about ⅕in.

In the venation of the wings this insect belongs to the true genus Cecidomyia, as defined by Osten-Sacken. In the genus Diplosis, which is near it, the second longitudinal vein curves downwards and reaches the margin of the wing below the tip. As regards specific distinctions, I have not sufficient material for complete comparison: possibly the presence of the curious and very loosely-attached black scales on the body may be a differentiating character.

Index to Plates XI. and XII.
Plate XI.—Eurytoma oleariæ.
Fig. 1. Gall on twig of Olearia furfuracea Reduced
Fig. 2. Section of ditto, showing enclosed insects.
Fig. 3. Larva × 12
Fig. 4. Head of ditto × 40
Fig. 5. Pupa extracted from case × 10
Fig. 5a. Pupa-case.
Fig. 6. Perfect fly × 10
Fig. 7. Antenna of male × 40
Fig. 8. Antenna of female × 40
Fig. 9. Foot × 40
Fig. 10. Spur on tibia and first joint of tarsus of front legs × 40
Fig. 11. Spur of tibia and first joint of tarsus of hind legs × 40
Fig. 12. Wings × 15
Fig. 13. Abdomen × 15
Fig. 14. Ovipositor of female × 30
Fig. 15. Penis of male × 30
Fig. 16. Spermatozoa of male × 1,000
Plate XII.—Cecidomyia oleariæ.
Fig. 1. Gall on twig and blisters on leaf Natural size
Fig. 1a. Section of leaf-blister.
Fig. 1b Section of gall.
Fig. 2. Bundle of eggs on young shoot Slightly enlarged
Fig. 3. Eggs × 10
Fig. 4. Larva × 10
Fig. 5. Head of larva × 40
Fig. 6. Pupa × 10
Fig. 7. Perfect fly, female × 10
Fig. 8. End of abdomen of female, at rest × 20
Fig. 8a. Ditto, open × 20
Fig. 9. End of abdomen of male, at rest × 20
Fig. 9a. Ditto, penis exserted × 20
Fig. 10. Wing and haltere × 10
Fig. 11. Antenna of female × 25
Fig. 12. Foot × 10
Fig. 13. Scales × 350
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Eurytoma Oleariæ.

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Cecidomyia Oleariæ.