On our Plume Moths (Pterophoridae)

ON OUR PLUME MOTHS.

7

ON OUR PLUME MOTHS.

BY THE REVD. DESMOND P .

MURRAY.

THE dependent association between Insect and Plant has been often commented upon. T h e close connection between the two Orders does not just mean that Flowers are fertilised by Insects or, in some instances, are altogether dependent upon them as has been so admirably shown by Darwin, Lubbock, Henslow and others, or other agencies bring about fertilisation : wind and the evolutionary construction of flowers themselves. T h o u g h not, therefore, an altogether new line of investigation, self-fertilisation seems to be one that has been somewhat neglected. But the link between the two Orders is a much closer one than is at first apparent, for Insects themselves are dependent upon Plants for their food and development; sometimes also for their protective resemblance ; and, to an even greater extent, for their distribution.

Just as these two Orders are thus closely associated, so may the twin studies of Entomology and Botany be termed inseparable.

A very striking example of this interdependence in the mutual economy of Insects and Plants has been pointed out by Meyrick in the case of the Pterophoridae, i.e. Plume Moths (Genera Insectorum, fasc. lOOme : Wytsman, Brßssels 1910). T h e theory he puts forward is that this Moth-family originated upon the continent of Asia, because there is found the greatest diversity of its generic forms. He infers that it must have originated, not only late in time but, at a period when Asia was completely isolated from other regions by wide seas : and that its exponents eventually gäined access to other continents, their present wide-spread distribution being explained by firstly their peculiar alar construction and secondly by their choice of food-plants. For the general structure seems especially adapted to secure extreme lightness, which facilitates distribution to be effected by wind without much eifort on the part of the actual insects : they possess very little muscular power, and are qiiite unable to fly against an even moderate breeze.

This negative mode of dissemination has gradually prospered : the diverse species have spread over the whole Earth's surface, including even the principal oceanic islands, and they have been found to exist in most countries wherein they have been sought.

Meyrick enumerates twenty-two genera, containing some 370 species, in the world. T h e high specific development of the two largest genera, i.e. Platyptilia and Pterophorus, would seem to be due to the large variety of situations and the abundance of suitable food-plants, best seen in the American kinds. Where specific pabulum is known, most kinds feed upon Dicotyledonous plants such as the Compositce which are the most highly organised of all phanerogamic plants : in the above two largest genera nine-tenths of the species are found to be attached to Compositce, all similarly

8

ON OUR PLUME MOTHS.

distributed by wind-blown seeds. A majority of the larvae are restricted to Gamopetalous plants, of not remote affinity and high in the scale of construction, such as the Labiatee and Gentianaceoe : this is true of the thirty-four Pterophorid.ce that alone occur in Great Britain and Ireland, where all are found to be associated with the same group of plants. Of all the known kinds, none have been found attached to Monocotyledons, the second great division of plants, though they are, as botanists agree, of earlier origin.

It is true perhaps that the vast majority of Lepidoptera are associated with the higher forms of plants, but such seems to be especially the case among the Plumes. In no other family of Moths, says Meyrick, is the predilection for plants of the highest development so marked and therefore we must regard the family as of comparatively recent origin. The later division of plants is supposed to have emerged in the Cretaceous period, certainly not earlier than the Eocene ; the former, Monocotyledons, is known long before that era. But it is not tili we rise to rocks of the Tertiary age, palseontologists teil us, notably those deposits at Florissant, Colorado and at Oeningen in Baden, that fossil Lepidoptera occur in any great varkty, and these are already referrable to Moth-families yet existent. Thus the supposition of comparatively recent origin seems to be quite justified ; and shows us something, if but a mere side-light, of the great value of those studies upon Pterophorida carried out by Edward Meyrick, authoi of the Handbook (1895) and Revised (1928) Handbook of British Lepidoptera, who died in 1938—cf. Trans, iv, p. lvi—after describing some twenty thousand species of Moths.

There is a group of Lycaenid butterflies, found almost exc usively in South Africa, that is known as P/iasis (Zeritts) ; and not until the last few years have certain of their food-plants been discovered. These are found to be, in some cases, families of Compositoe and Zygophyllacece, which pabulum is very exceptionable among Rhopalocera. It will be interesting to trace their origin, when a greater number of facts about their life-histories have been ascertained. They are highly specialised Insects, whose larvae bear tubercle-processes to ward Ants away from their honey-gland ; whose eggs are covered with scales from the female Butterfly's b ^ d y ; whose pupse undergo their eedyses under ground, &c (cf. Dickson, Annais S. Afr. Mus., 1940, xxxii, pt. 6).

Also in the south Ethiopian region are certain day-flying Moths, associated with particular families of Plants, for whose fertilisation they seen necessary (Murray, Entomologist, 1933, lxvi, p. 104).

Nearly fifty years ago Mr. J. W. T u t t published a small volume on the British Plume-moths, now become a rare book and difficult to obtain* ; but, since then, a great many additional facts have * " T h e M o n o g r a p h of t h e British P t e r o p h o r i n a " of 161 p p . , issued in Parts at sixpence apiece, of w h i c h the last a p p e a r e d in N o v . 1 8 9 5 . — E d .

ON OUR PLUME MOTHS.

9

accumulated, even though few species have been added to our list. A very helpful and practical note, given by Mr. T. Bainbrigge Fletcher on the food-plants of Plume-moth larvse, will be useful regardingour native kinds (Ent. Record, 1939, Ii, p.76). Though the life-histories of most of our species of these delicate and beautiful Moths are now described, few have hitherto been figured in their early stages, as far as I can ascertain.

The following account and illustration, in all its states, of one of the more common species Platyptilia gonodactyla, SchfL, will therefore be welcome to many Lepidopterists. It is hoped that other Members will work out their local species and make figures of the early stages as opportunity arises : they are too small to photograph.

O V U M (Fig. 1, magnified 2 5 times).—The eggs are deposited singly, at the end of May or beginning of June, on the woolly underside of the leaf of the food-plant, and never more than one egg on a single leaf. At first the egg is creamy-white in colour, and half buried in a cushj#n of wool; the surface is shining, with no tracery pattern. Later it turns slightly greenish and, at füll development, pale yellow when the larva is about to emerge after a week or ten days.

LARVA (Fig. 2 , in first skin, x 5 0 ; fig. 3 , fully grown, X 6 ; and 7th segment of same larva, greatly magnified).—The larva is a tiny object of about \ mm. in length ; yellowish-white, with head black. It burrows into the soft tissue of the leaf-surface, continuing to feed through June and July, and Coming to füll growth during August, when it is pale green and about 9 mm. in length. There is a second brood in autumn, of which the nearly fully grown larva hibernates from October to April, and comes to maturity early in May. PUPA (Fig. 4 , magnified thrice).

The pupa is attached at the tail extremity, by (Fig. 4, X 12) cremastral processes, to the stem or sometimes amongst the fluffy seed-heads of the food-plant, and very closely resembles a bract of that plant. Hibernating larva, that pupated on 2 May, emerged as imago on 31 May ; but, in the summer brood, the pupal duration decreases as temperature rises.

IMAGO (Fig. 6/3, x 5, and single scent-scales).—Measurement 20 mm. The front wings are ochreous or of a greyish tint, strongly marked with a dark triangular blotch on the costa and with some silvery scales. The divided hind wings are dull brown, the dorsal cilia or lower surface holding spine-like black scales which Meyrick found present in every species he examined through out this family and uses as an absolute character to distinguish its species. In the absence of other explanation and the habitual association of black pigment with sense perception, it is conjectured that these scale-tufts are some kind of sense organ. The resting

10

A N OLD SUFFOLK

NATURALIST.

attitude (Fig. 6a) is peculiar : the hind legs are held straightly under the abdomen, and the Moth has the habit of rolling its wings round into a tiny cylinder which is held out at right angles to the body, as if it were pointing with a finger in two opposite directions: hence the significance of another kind's name, monodactylus i.e. one-fingered. The males (Fig. 8, genitalia X 50, after Pierce), seem to be much more numerous than the females : out of twelve imagines, taken in flight on two successive nights, all were males. The venation (Fig. 7, X 10) is of special interest for, in spite of the deep fissures in the hind wings, the nervures (numbered) retain their noimal form.

F O O D - P L A N T (Fig. 5 , nat. size, showing bracts) is exclusively Coltsfoot Tussilagofarfam, Linn., a widely spread plant and a weed ditficult to eradicate.

AN OLD

SUFFOLK BY

HIS

NATURALIST.

SON.

M R . G A R R E T T G A R R E T T was born in Ipswich during 1808, son of Jacob Garrett (1774-1833) of St. Margarets Green there. He was educated at Ipswich Grammar School in Foundation-street, under Dr. Riguad. And to him his father bequeathed the iron-works occupying no. 14-16 Cobbold-street in St. Margarets; he is described as iron merchant, though living in Victoria-terrace there in 1846 PO. Directory, but the firm is named as Elizabeth Garrett and Son, St. Margarets-green, in White's Directory of 1844, so presumably his mother died in 1845. His two sisters shared the partnership with him, who carried on the business of iron ' gate, palisade, &c, manufacturers ' at their desire though his heart was in scientific pursuits. ' If my father had been really interested in his trade, he could have been very successful, as his was the only such works in Ipswich when he took it Over : no Ransomes, no Turners or Masons at that time. But he left the business to the mismanagement of a manager who, I fear, looked after himself and caused my father's failure : a case of the Square man in round hole,' his son considers in lit. White shows that by 1874 he had been replaced as owner by John Cooper and Co., ironfounders of the same address in St. Margarets, who in 1885 were still at no. 14 though now termed wheelwrights ; when ' Mr. Garrett Garrett of 30 Palmerston-road ' is among Ipswich's principal inhabitants.

That year there were in the town also Mr. John Garrett of Newtonroad and Abiather Garrett, corn-merchant's manager, of 45 Tanners-lane ; Jarrold's Direct. Ipswich 1890 shows Herman of