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Psyche 2:137-153, 1877.

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PSYCHE.
ORGAN OF THE CAMBRIDGE ENTOMOLOGICAL CLUB EDITED BY GEORGE DIMMOCK AND B. PICKMAN MANN. Vol. 11.1 Cambridge, Mass., May-August, 1878. [Nos. 49-52. On Larvae of Tineina, especially of Lithocolletis. In PSYCHE, v. 2, p. 81-87, I have alluded to the discovery by Dr. Clemens of two larval forms of Lithocolletis in this country, and have stated that in some species of what Dr. Clemens calls the second or flat group I had observed a modifi- cation which I called the intermediate form, under the impres- sion that it afforded a connecting link between the second group and that which Dr. Clemens considered the first or cylindrical group ; coupled however with the suggestion that this supposed intermediate form might prove to be only a later stage of growth of the flat form. This suggestion proves to be the truth ; the intermediate form is the last larval state of the flat form, and is also a connecting link between the first and second larval groups. As hereinafter stated, however, the larva at this stage undergoes a change of form without moulting, and fig. 3, 11. 83, represents it at one point only of this larval stage. This is, however, not the only connecting link between the two groups, for L. ornatella of itself forms another, group, and at the same time affords another connection between Dr. Clem* ens' first and second groups, as well as connecting both with Dr. Clemens' genus Leucanthiza. But notwithstanding that the larvae of all three groups are thus connected, the groups are distinct and well marked, so that, in a large collection, ninet-y- nine out of every hundred would, without hesitation, be re- ferred to its appropriate group. But while this is trueit is also true that the larva of all the groups resemble each other closely on their emergence from the egg, and are almost indistinguish- able in the latter part of the last larval state, and the pupae are



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entirely so.
Starting from a common point, or nearly so, they diverge from each other to converge and meet again in the lat- ter part of the last larval stage.
(In illustration of these life-
histories it will be necessary to refer again to the figures on page 83. In fig. 2 I have not made the dentation of the man- dibles distinct enough.)
Concealed as these larvae all are within their mines, inside of leaves, and dying as they inevitably do when removed from the mines, it is somewhat difficult to trace accurately all the larval changes ; but by watching them closely, by collecting large numbers of larvae in all stages of growth, and comparing them, and by pursuing the same process with the cast skins in the mines, and counting them, I believe that I have succeeded in tracing the larval histories of many species ; and while the lar- val history of each group is materially different from that of the others, that of the species of either group does not differ in any important respect from that of others of the same group. There are, however, many points common to all the groups, and I give these first, accompanied by some general remarks upon their characters and affinities, and followed by a statement of the points peculiar to each group; giving thus a brief life- history of the genus, and of each of the three groups, rather than life-histories of separate species ; together with notices of such relations of the genus to others as seem to be indicated by the larval characters.
I have never seen the unhatched egg of Lithocolletis ; but upon the spot at which the mine begins, and while the mine is yet scarcely visible to the unaided eye, may be seen, under the lens, a glittering point.
This is the shell, or rather cho-
rim.
It is perfectly flat, and one might almost say that it ,
is imbedded in the
substance of the leaf; its outline is oval, and it does not vary much in size in the different species, being usually about 0.34 mm. long and half as wide. The mine begins under the egg, the larva passing obliquely into the leaf because the structure of the head and trophi is such that it cannot enter the leaf vertically, as do the larvae of some other genera. As shown in figs. 1 and 2, the head of the larvae of the flat group projects straight forward and can neither be elevated nor de-



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pressed; the jaws project in the same way beyond the head, and can neither be elevated above nor depressed below the axis of the body; this is equally true of the larvae of the other groups in their earlier stages. Such a larva placed upon the surface of a leaf could never enter it, but must perish; but, when the egg is so imbedded in the surface of the leaf, and so firmly attached to it, the larva, in passing obliquely out of it, necessarily enters the leaf. This affords a sufficient reason why a larva once removed from its mine always dies, so long as the structure of the head and mouth-parts retains this character (figs. 1 and 2); though no good reason, apart from the crea- ture's instinct, can be given why it might not, after the change occurs, which takes place in all at some period, and after the trophi become like those of ordinary larvae of Lepidoptera, as shown in fig. 4, re-enter the leaf, and form a new mine, as do ' the larvae of many other genera (e. g., some species of Gracil- aria, Ornix and Laverna), or feed externally, like the greater number of lepidopterous larvae. But, as a matter of fact, it never does so.
Dr. Clemens has stated that the larva of L. crataegella, when feeding in leaves of the wild cherry (Prunus serotina), sometimes leaves one mine and makes another. If this is true, its habit is unique in the genus ; but, though I am very familiar with this species, I have not been able to confirm Dr. Clemens' statement, and I have found reason to think that lie was in error. Ornix prunivorella Cham. was unknown to Dr. Clemens. It mines the leaves of Prunus serotina, and its mine cannot be distinguished from that of L. crataegella Clem., and, like other species of Ornix, it does leave one mine and make another. I think it at least probable that Dr. Clem ens mistook the Ornix mine for that of L. crataegella. To return from this digression. After leaving the egg, the mines of all the species of Lithocolletis that are known to me, as well as those of many other genera of Tineina (e. g., Phyl- locnistis), are at first linear and confined to the surface, upper or lower, as may be the habit of the species. Larvae with the trophi as in fig. 2 (e. g., Phyllocnistis, Lithocolletis, and very young Gracilaria) simply separate the epidermis from the pa- renchyma, and do not eat the latter. The linear part of the



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140
mine of Lithocolletis is very similar to a Phyllocnistis mine ; and during the portion of the larval life when this mine is made, and indeed in the flat and ornatella groups throughout the entire larval life, except in its last stage, the mouth parts (fig. 2) are identical with those of Phyllocnistis. So long as this char- acter of the trophi is present in all these groups the body is depressed or flattened, the sides of the segments are mammil- lated, and the legs are but feebly developed. In all of these respects the larvae resemble somewhat those of Phyllocnistis. Prof. Zeller, as quoted by Mr. Stainton in Ins. Brit., v. 3, p. 285 (I have not seen Zeller's paper myself), gives as one of the characters of Phyllocnistis 6b larva apod," and Dr. Clemens, in Tin. N. Amer., p. 83, states that' the "larva is without feet or prolegs." As to the earlier stages of its larval life, this is no doubt true, but as to the later stages,its truth depends on what is meant by being lb without feet or prolegs." Tlie next three segments after the head, the last and the penultimate segments .
are certainly without appendages of any kind; but on each side of each of the other segments, not, it is true, at the point usually occupied by the legs, but projecting obliquely from the edge of each segment, I find, in P. ampelopsiella Cham., a very distinct two-jointed appendage, without either claw or circlet of tentacles, which certainly aids the larva in its slow progress through its long and narrow mine. It is not pretended that these append- ages are hon~ologous with even the feebly developed legs and prolegs of the young Lithocolletis larvae, yet I do not see why they are not as properly called legs as those of a Nepticula. Tlie resemblances of the larvee of Lithocolletis to those of Phyl- locnistis lie in the thin and flattened body, the mammillated sides of the segments, the character of the trophi (fig. 2), and the linear character of the mines. The next three segments after the head are somewhat enlarged in the first stage of Litho- colletis, as in many other genera (e.g., Gracilaria), but this is not like the great lateral enlargement of the same segments in Phyllocnistis. The legs (fourteen in number) are present in all the three groups of Litliocolletis, though they are feebly developed in all stages of the flat group, in the first five stages of the cylindrical group, and in all except the last stage of L.



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ornatella, so that they are unfit for crawling, when the larva is removed from the mine, in all except the last stage of A. orna- tella, which voluntarily leaves the mine and crawls away to pupate. No good reason can be given why the cylindrical larvae, after their fifth stage, when the feet are apparently large and strong enough for use, seem unable to crawl when removed from the mine. When out of the mine they apply the spinneret to the surface on which they rest, and spin a thread fit to afford a secure foothold, as do most crawling larvae, but they are unable to crawl, and yet if, while tumbling helplessly about, the true feet happen to touch a part of a mine from which the upper cuticle has been removed, the larva at once drags itself upon the mined portion, and then crawls actively enough, without attempting to spin a thread for a foothold. From each side of each segment project three hairs, just above which are two other shorter ones. These hairs are found in all the groups, and persist throughout the larval life. I have mentioned above the Phyllocnistis-like character of the trophi and of the mine in the earliest stages of Lithocolletis. Indeed, while this character of the trophi is retained, this char- acter of the mine results as a necessary consequence. The larva can only feed straight on or turn to one side or the other, merely separating the cuticle from the parenchyma, and cannot deflect the head so as to eat out the latter, as a mining larva with the head deflexed and the trophi as in fig. 4 would do. The form of trophi in fig. 2 is found in the earlier stages of some other genera besides Phyllocnistis and Lithocolletis, and in such cases the mine is usually linear and is always a mere sep- aration of the cuticle from the parenchyma. It need not be linear. Indeed, in Phyllocnistis ampelopsiella, though the mine is, strictly speaking, linear, yet it winds about from the midrib to the margin and back, between the veins of the leaf, until the entire cuticle in the mined portion is separated, and the mine becomes a blotch. In Lithocolletis and many other genera, the mine always becomes blotch-like. Frequently, as in 5. orna- tella, the blotch obliterates the linear part of the mine, but in other cases, as in L. celtisellh, the linear part is long, and the blotch is at one end of it, like the mines of some Nepticulas.



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The period during which this form of trophi (fig. 2) lasts varies in different genera and in different species of the same genus. Thus, in Phyllocnistis, it lasts until the last larval stage, when the form in fig. 4 is assumed, and the larva immediately spins its cocoon. This is also the case in the flat and ornatella groups of Lithocolletis ; but in the cylindrical group the change takes place at the fifth stage, as it does also in Gracilaria (Parectopa) dniella Clem., and probably in other species of the Euspilap- teryx group of Gracilaria, while in such species as G. rhoisella and G. blandella, which I call true Gracilaria, it takes place at the second stage.
But while larvaa having trophi as in fig. 2 must make linear or flat mines, the converse does not hold good. Many larvee,
like those of Nepticula, Bedellia, Aspidisca and Antispila, make linear mines, at least in their earliest stage, but the trophi of these are of the ordinary type of lepidopterous larvas (fig. 4), and the head is deflexed, the mouth not being fixed in the axis of the body. But in such cases the mine is not a mere separa- tion of the cuticle from the parenchyma ; the latter itself is eaten out. Gracilaria robiniella and G. salicifoliella, after the moult at which they assume the trophi as at fig. 4, also continue making flat blotch mines, but the parenchyma is eaten out. In these two species of Gracilaria and in others having similar habits, the body never becomes cylindrical, but is always some- what depressed, and the head is very flat and thin, even after assuming the form of trophi, as in fig. 4. This form of trophi is assumed sooner or later by all lepidopterous larvas; in some, as above shown, not until a late stage of larval life, in others earlier. In the great majority of species it is assumed before the larva leaves the egg; if this is taken to indicate a high rank, then Nepticula, instead of taking the lowest place among Tine- ina, as in Ins. Brit., v. 3, should out-rank Lithocolletis and even Gracilaria; and Tischeria also would out-rank Gracilaria because the larvas of Tischeria assume the form given at fig. 4, either before leaving the egg or at the first moult thereafter. In describing mines, they are frequently mentioned as being either tentiform or flat. But from what is written above it will be seen that this is not the true distinction. It is rather between those in which the parenchyma is eaten out, and those in which



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it is simply ~eparat~ed from the cuticle ; whether it is the one or the other is a necessary consequence of the structure of the head and trophi. At whatever period of larval life the moult takes place, at which the form in fig. 4 is assumed, the character of the mine is changed at once ; and thereupon the larva, as in the cylindrical group of Lithocolletis and in Gracilaria, proceeds to eat out the parenchyma, or leaves the mine ; or, as in the flat and ornatella groups of Lithocolletis, and in Phyllocnistis, at once ceases to feed and spins its cocoon, to do which L. ornatella leaves the mine. In the cylindrical group and in Gracilaria, the larva, after that change, finds itself unable, from the position of the head and the structure of the trophi, to continue to separate the cuticle from the parenchyma, and must feed upon the latter; and the body having assumed a more cylindrical form, the cut$icle presses uncomfortably on it ; this leads the larva if it continues to mine, as in Lithocolletis, to meet its changed condition by making its mine into a tentiform one, or, as in most Gracilaria, to leave the mine and feed externally. Some of the latter also, as (7. erigeronella, make the mine tentiform ; others, with more flattened bodies, as G. robhiella, make sufficient room by eating out the parenchyma. Previous to this change there is no indi- cation of any instinct to spin a web, probably because there is no organ to elaborate the silk, or to spin it. It is at this change '
that the silk glands and the spinneret first appear, just in time to meet the wants of the larva, which could neither give its mine the tentiform character, nor subsist externally, without the ability to spin. The tentiform character of the mine is caused, in part at least, by the shrinkage of the silken web; and to secure its hold on the leaf, as an external feeder, the larva must spin a few threads upon the surface. Large larvae no doubt aid in curling the leaf to make the mine, or to feed externally, by drawing the silken threads; but in small larvae this is accom- plished mainly by the contraction of the silk itself. In the Nat. Hist. Tin., v. 2, Mr. Stainton enumerates seventy-six species of Litliocolletis as known in 1857, and many others have been discovered in Europe since that date. In my Index in the Bull. Geol. Geog. Surv., v. 3, seventy American species are enumerated. The total number now known is



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probably near two hundred.
There is no published account of
the occurence of the flat larva in Europe, and it is not probable that it would
have remained unnoted had it been found there. In this country the flat group is represented by only fourteen species, and L. ornafeZ7a is the only species of its group as yet made known. All the other species belong to the cylindrical group. Though the species of the flat group are comparatively so much less numerous, the individuals are as numerous as those of the cylindrical group. So far as the mines are concerned, this might be explained by the fact that the mines of the flat group are always on the upper surface and are large, conspicuous blotches, while those of the cylindrical group are smaller, and with the exception of L. tiliaeella Cham. and L. robimella Clem. in this country, are always on the under side ; but this will not explain the greater abundance of the moths of the flat group. This is owing, as I believe, simply to the fact that they are more prolific. The larvse of this group are gregarious, while it is a comparatively rare thing to find more than one larva in a mine of the cylindrical group.
The larval life of a Lithocolletis lasts, in Kentucky, in mid- summer, about three weeks. Many species, however, pass the winter in the larval state, though their development may be hurried by keeping them in a warm room ; then the moths make their appearance irregularly, according to temperature, all through the winter. It is probable that the larval life can not be shortened to a less time than three weeks. Since the larvas cannot be removed from one mine to another, and it is difficult to keep the leaves green and fresh fur so long a time, the only way to determine the length of the larval life is by observing a multitude of mines in various stages. From such observations, repeatedly made, I find the length of larval life to be about three weeks. In this period the larvae moult eight times, at the eighth moult passing into the pupa state. This seems to be a large number for so short a life-time, but I am convinced that it is correct. I have already alluded to the difficulty of cletermin- ing this matter accurately as to larvse which are concealed in their mines, but I have observed hundreds of the larvae in various stages of growth, and I find always seven distinct sizes in each



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species, and I find an eighth form different structurally from all the others, but no larger, or rather no longer than the seventh ; and although 1 have not seen the unhatched egg, I have removed larvae from mines which had not extended to the length of the egg from it, so that I am certain of having seen the first stage. At each moult except the seventh, the length of the larva in its first stage is added to that of the moulting larva. Thus L. coryliella Cham. and L. guttifinitella Clem. are each in their first stage 0.56 mm. long. In the second stage they are 1.13 mm., and in their seventh stage 3.95 mm., and in several complete series of specimens now before me 0.56 mm. have been added at each moult. L. ornatella Cham. is at first 0.52 mnl. long, and in its seventh stage it is 3.63 mm. long. In L. rubiniella and in L. crataegella a somewhat different rule prevails. L. robiniella is at first 0.63 mm. long, at its second stage it is 1.26 mm., and so on to the fifth stage, when it is 3.15 mrn. long. At its fifth moult there is no increase in size, but its form is changed from moniliform depressed, to a nearly cylindri- cal larva, the trophi have changed from the form given in fig. 2 to that given in fig. 4, and the legs are much better developed. In other words, in the cylindrical group a change takes place at the fifth moult, which is equivalent to that which takes place at the seventh moult in the flat and ornatella groups, and which takes place in Phyllocnistis at its last moult before becoming a . pupa, which is.probably also its seventh. At their sixth moult, however, L. robimella and similar species add their original length again, and continue to do so at each subsequent moult, including the seventh, at which they pass into the last larval or the prepupal state, thus differing from the larvae of the flat and ornatella groups, which at this moult do not increase in size, but simply change their forms and structures. In these latter groups the first seven stages are stages of nutrition andgrowth, not apparently of development; but the seventh moult and eighth stage are stages of development, and not of growth. In the cylindrical group all the stages are stages of growth and nutrition, except at the fifth moult. The changes which take place at the seventh moult in the flat and ornatella groups, and which continue to progress gradually through the eighth stage



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in the flat group, are necessary to bring these larvae up to the level of the cylindrical group in its sixth and subsequent stages ; except that the legs of the flat group are never so well developed as they are in the cylindrical group after the fifth, and in L. ornatella after the seventh moult. With this exception, the larvas of all the three groups have reached the same level at the end of the eighth stage.
I am not positive as to the length of any one stage of larval life except the last (eighth), and of that only in the flat and ornatella groups. In these it lasts between two and three days in the summer, but the fall broods pass the winter in this stage. The moult by which the larva passes into the pupa state is dif- ferent from the previous larval moults. The cast skins of the very young larvae are usually lost in the frass in the mine ; this sometimes happens with the older skins, and I have opened mines of larvae in their penultimate stages, when only a single skin could be found. Usually, however, three or four may be found. In moulting, the head is first loosened cornpletely~ and retracted out of its skin, the suture between the head and next segment opens on the under side, and the opening extends back along the sides of the next two segments, upon the upper surface of which the head is thrown back ; the larva in its new skin wriggles out at the opening, and very frequently the head is entirely torn off. The skin thus cast is thick and hard, and that cast at the seventh moult frequently remains almost entire. But the skin cast at the eighth moult is thin and delicate, and is usually torn into shreds, which are pushed off to one side in tlie cocoon, forming a little heap. As this moult takes place in the cocoon, it of course can only be observed by opening the latter, which usually injures the pupa or stops the moulting process. In a specimen of L, ornatella thus opened, I found some shreds of the skin pushed back to the apex of the abdomen, others adhering to parts of the body, and the skin entirely or partly removed from some of the feet, and uninjured on' others. It had the appearance of a pupa which was freeing itself from its larval skin by wriggling about against the sides of its cocoon. In the latter part of its last stage tlie cylindrical larva becomes white, having previously passed from the white of its earliest



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stages to pale greenish.
The larvae of the flat group, yellowish
or whitish in their earlier stages, usually become more or less tinged with a smoky or fuscous hue, sometimes almost blue- black, but at their seventh moult they again become white. The larva of L. ornatella, at first whitish, gradually becomes tinged with green, which deepens in its last and penultimate stages to a peculiar bluish green not found in any other larva of the genus. This hue persists in the earlier part of the pupa state.
The pupa has the head pointed in front, with a serrated edge running back on each side, which is no doubt useful in cutting through the cocoon, while it pushes itself out by the contortions of its body, aided by the microscopic bristles which arm the upper surface of the abdominal segments. The pupa does not entirely free itself from the larval skin for nearly two days after the cocoon is made, and the pupa state lasts about eight days A
after that, at midsummer, and the moth emerges through a rup- ture of the pupa skin across the back of the head and down the sides of the wing-cases.
In this latitude these insects may be found in all their stages from May to the fall of the leaves. I have plucked from the same plant of Bus toxieodendron, at the same time, leaves containing larvae of L. guttifinitella in all their stages, as well as pupae, and pupa-skins from which the imago had emerged. It is therefore manifestly impossible to say how many broods may succeed each other in a season. That depends on the tem- perature and length of the season. In Kentucky I have found Gradlaria robiniella mining locust leaves from the first of July to the fall of the leaves in October; while I have found it doing the same thing in New Orleans in December, when the leaves were falling. Larvae which are in their last stage, having finished feeding, may winter in that stage, and this is the condition in which they are usually found in the winter, the temperature preventing them from passing into the pupa state till the return of warm weather. Larvae which have not finished feeding when the leaves fall must of course perish, but no good reason can be given why pupae might not winter. Nevertheless, I have never met with a Lithocolletis pupa in the winter or spring.