Part 64

In connection with this subject, it is noteworthy that the flattened extremities of the elytra of the beetle, Ectopsis ferrugalis, closely resemble in both shape and colour the remarkable anterior segments of the larva of D. atronivea. As both insects feed on the same plant, and thus exist under very similar conditions, it is highly probable that the peculiarities have been independently acquired in each species for similar purposes.

The pupa is enclosed in a light cocoon amongst dead leaves, &c, on the surface of the ground.

{96}The perfect insect appears in February and March, and may sometimes be taken at blossoms in the evening. It is also attracted by light, and has been found occasionally, in the daytime, resting on tree-trunks. It hibernates during the winter, coming abroad again the following spring to lay its eggs. I have observed that a good many pupæ from the autumnal brood do not emerge until September or October, so that the insect evidently spends the winter both as a pupa and as an imago.

DECLANA EGREGIA, Feld.

(Chlenias egregia, Feld. cxxxi. 24; Fereday, Trans. N. Z. Inst. xii. 268, pl. ix. 2. Detunda egregia, Meyr., ib. xvi. 101.)

(Plate X., fig. 35.)

This very handsome insect has occurred in the South Island at Nelson, Christchurch, Akaroa and the Otira Gorge.

The expansion of the wings is about 1¾ inches. The fore-wings are creamy-white; there is a small dark brown mark at the base, a broad transverse wavy brown band before the middle, a very large four-cornered irregular brown mark beyond the middle, one of its corners touching the apex and the other the tornus; the termen is shaded with pale grey, and there is a series of faint brown marks on the costa and dorsum. The hind-wings are dull white, darker towards the termen; there are two very faint transverse lines.

The perfect insect appears from November till February. It is a very rare species.

Described and figured from a specimen in Mr. Fereday's collection.

DECLANA FLOCCOSA, Walk.

(Declana floccosa, Walk. xv. 1649. Argua scabra, Walk, xxviii. 448. Declana feredayi, Butl., Proc. Zool. Soc. Lond. 1877, 398, pl. xliii. 5. Declana nigrosparsa, Butl., Cist. Ent. ii. 500. Declana floccosa, Meyr., Trans. N. Z. Inst. xvi. 102.)

(Plate X., figs. 39 to 43 varieties, 44 to 47 ditto.)

This species has occurred very commonly at Wellington, Christchurch and Dunedin. It is probably generally distributed throughout the country.

The expansion of the wings is about 1-3/8 inches. The fore-wings are pale greyish-white with numerous small brownish-black streaks, exhibiting a slight concentration near the apex. The hind-wings are dull white, clouded with greyish towards the termen.

This insect is so extremely variable that I have given descriptions of a few of the principal varieties below; all these forms may, however, be connected by specimens exhibiting every intermediate gradation both in colour and in markings.

1. Fore-wings with several large brown spots near the middle.

2. Fore-wings covered with numerous black spots (formerly known as Declana nigrosparsa) (fig. 47).

3. Fore-wings with two more or less conspicuous curved black or brown lines from costa to dorsum (figs. 41, 42, and 44).

4. Fore-wings with these transverse lines joined by two others running parallel to dorsum and costa.

5. Fore-wings with transverse lines and black spots (fig. 43).

6. Fore-wings diffused with dark greyish-black, except two broad bands of the original light colour extending from costa to dorsum; hind-wings darker than usual (fig. 45).

7. Fore-wings with a dark brown central band; hind-wings clouded with dark brown towards termen, with a faint curved transverse line near the middle (figs. 39 and 40).

All these varieties occasionally have tufts of orange-yellow scales on both the wings and on the body, and they also vary in other minor particulars (fig. 46).

The egg of this insect when first laid is oval in shape and light green in colour, becoming bronzy a few days before the emergence of the larva. The young larva is very attenuated, with only ten legs. {97}Its colour is pale yellow striped with brownish-pink near the segmental divisions. It is very active, and does not devour the egg-shell after emergence.

The full-grown larva has the body much flattened underneath. In colour it is pale brownish-pink, with numerous irregular darker markings, which in some specimens almost form two broad subdorsal lines. The under surface of the larva is pale green. There is a series of fleshy filaments of a pinkish-brown colour along each side of the insect, and an extra pair of prolegs on the ninth segment.

This caterpillar is, however, very variable, its colouring appearing to depend largely on its surroundings. The favourite food-plants are Leptospermum ericoides and Aristotelia racemosa. The larvæ found on the former plant are usually pale yellowish-brown, whilst those from the latter are much darker brown, often mottled with grey like the stems of the Aristotelia. A specimen I once found on a mountain beech (Fagus cliffortioides), the gnarled stem and branches of which were covered with grey lichens and mosses, was mottled with the most beautiful shades of greenish-grey. These larval varieties are very interesting, and in order to test the direct influence of food on the colouring of the larvæ, I once divided a batch of eggs deposited by a single female into two equal parts, and fed one half on Aristotelia, and the other half on Leptospermum. The differences in colouring between the two lots of larvæ thus treated were, however, of the most trivial description. This somewhat surprised me at first, as I had previously observed quite distinct varieties on each plant, when found in a state of nature. Hence I am now disposed to think that these differences have been brought about gradually, by natural selection acting on larvæ feeding on the same plant for a large number of generations. By this means a sufficient amount of variation might be accumulated, to cause the closest possible approximation in colouring to the stems of the several food-plants. It is also noteworthy that many of these food-plants grow in widely dissimilar localities, so that the free inter-breeding of insects dependent on them would not be likely to occur, and thus the peculiarities of colouring adapted to the stems of each food-plant would not be disturbed by the effects of inter-breeding.

In connection with the foregoing experiment it is also interesting to observe, that the specimens fed on Aristotelia matured much more rapidly than those on Leptospermum; the former plant evidently being the more nourishing food for the larvæ. Also that out of the batch fed on Aristotelia 28 became moths, of which 12 were males and 16 females; whilst out of those fed on Leptospermum only 24 became moths, of which 15 were males and 9 females. In all other respects, excepting food-plant, the two lots of larvæ were subjected to identical treatment.