A Study of First Instar Larvae of the Saturniidae

JOURNAL OF THE LEPIDOPTERISTS' SOCIETY

Volume 14 1960 Number 2

A STUDY OF FIRST INSTAR LARVft OF THE SATURNIIDft, WITH SPECIAL REFERENCE TO NEARCTIC GENERA

by ROGER W. PEASE, JR.

INTRODUCTION

First instars of many species of Lepidoptera have been described, usually with non-comparative and non-technical descriptions. Occasionally it has been done with an eye toward interpreting structures of the mature larvre and correctly homologizing them with those of other groups. This has been singularly successful, since the first instar represents a link with the past in that primitive characters may occur in this stage which are completely modi fi ed after the first molt. This p

89 90 PEASE: First instar larva: Vo1.14: no .2

fication of larvee, the color figures are, of course, unsurpassed, but they should not be considered structurally complete. FRACKER (1929) constructed a key to the mature Iarvee of North American Saturniid~ using his system of Greek letters to identify setee. Char acters used in his key will sometimes hold for the first instar. Particularly important are the relationships of the most dorsal set~ on segments eight and nine of the abdomen. In the following discussion the setal nomenclature of GERASIMOV (1935) as modified by HINTON (1947) is followed as closely as possible. The almost mathematically precise definitions of groups of setee could be a.pplied to the Satu rniidee even though this family was not included in HINTON'S paper. The notations of FRACKER, FORBES, or HEINRICH are alternate systems. For comparisons and synonymy see HINTON (1947) and PETERSON (1948). Those setee which occur throughout the Lepidoptera in the first instal' are called primary setee. Secondary setee appear in succeeding instal'S but are usually absent in the first. It is an indication of advancement in the Satur niidee that some of them have numerous secondary seta~ in the first instar. HINTON recognized two types of setee: long or tactile setee and microscopic or proprioceptor setee. The former are generally distributed over the body, while the latter are restricted to areas where overlapping of cuticle is likely to occur, such as at the juncture of segments. Most of the microscopic setae on specimens preserved in alcohol were not clearly visible with the resolution and magnification (150X) used. Except for a single series of aberrant H emi feura larvae, the microscopic setee will be omitted from this discussion. Characters such as crochets, head structures, and thoracic legs are prob ably as diagnostic as body setee, but they have not been so widely used and are less easily studied. Some reference will be made to the crochets on the prolegs. All structures except the most prominent may be ruined if specimens preserved in alcohol were ever allowed to dry out. The more conspicuous seteeare usually in satisfactory condition even in some of the most severely shrunken specimens. It is hoped that the key presented here will eventually be extended to include all the prominent structures of first instal' larvae. A few terms need to be redefined for use with the first instar. If a seta is referred to as PRIMITIVE, it consists of a single stiff filament rising di reetly from the body wall. Presumably, this is the ancestral form. Chalazee are extensions of cuticle bearing one to several setee. FRACKER (1929) de fines scolus as a "spinose projection" of the body wall, with reference to the Saturniidee. The scali of later instars, however, ,are homologous to structures in the first instar which are clearly divided into a chalaza and a seta. Here the term CHALAZA will be used for any projection on the body wall bear ing primary setee which are still distinguishable from secondary setee. SCOLDS will be reserved for simil,ar structures in the Saturniinee having secondary setee on the chalazee which cannot be separated from the primary setee. As a general rule, the setee of first instar larvee of Saturniidae never be come fused . It is the chalazae which are fused to a varying degree. For ex- 1960 Journal of the Lepidopterists' Society 91 ample, on the dorsomeson of the ninth abdominal segment, all Hemileucime have a single chalaza. This bears two primary setre, one from each side of the body, whose chalazre are united. Very rarely an individual larva will hav.e 'a seta split or forked, but in two individuals seen (one each of Arsenura and H emileuca), the fork occurred on only one side of the body.

PRIMARY AND SECONDARY SETIE

The :primary setre are divided into several groups defined by their position and recurring on each segment. They are: dorsals (D 1 and D2), subdorsals (SD1 and S02), laterals (Ll and L2), subventrals (SVI and SV2), and ventral (VI). In addition there are two extra setre (XD1 and XD2) on the cervical shield of the prothoracic segment. The homologies of the setre on the tenth abdominal segment are not clear at present. The abbreviations T-l, T-2, T-3, and A-I to A-lO will be used to indicate thoracic and ab dominal segments numbered from anterior to posterior. When fusion of chalazc.e takes place, it occurs first within groups of setre and then between different groups. Only the letters of the setal groups will be used to describe such united structures. For example, D would refer to a structure homo logous to the dorsal setre (D1 and D2) and XD-SD would be a structure made up of the two SD setre combined with the two XD setre of the pro thoracic segment. On the cervical shield of the prothorax (T-1) there are six primary setre. In most Saturniidre four of these are represented by two large bifurcate chalazc.e or scoli on the anterior :part of the shield and two primitive setre on the posterior margin (Fig. 1). In the Saturniinre the bifurcation has disappeared, and the two scoli bear numerous secondary setre. Anthercea and A elias show increasing degrees of fusion of the bases of the two scoli, the top being plainly double in the former and single in the latter (Figs.3 and 4). On the posterior edge of the plate, two single setre rise directly from the shield without chalazre. One is usually mesocaudad of the first chalaza, and the second is about midway between the two chalazre. Dryocampa rubicunda (Fig.2) offers a chance to observe the relationships of the setre when their chalazre are reduced and almost wholly absent. The se-tre of the more dorsal anterior pair are of subequal length, while one seta of the pair below them is longer than the other. In the higher Lepidoptera, XD1 and XD2 are of equal length and are on the anterior 'Part of the cervical shield. The subdorsal group (SD1 and SD2) is below these with SD1 longer than SD2. The dorsal group (D1 and D2) forms the remaining setre, with D1 shorter and more dorsal than D2. Therefore, in the Saturniidre the more dorsal of the two anterior pairs of setre on the cervical shield will be called XD, the more lateral SD, the more dorsal of the single setre D1, and the more lateral single seta D2. D1 and 02 vary in their length relationship. Those on T-l are of nearly equal length in most Saturniidre. In Eacles imperialis D1 is bullet shaped and much shorter than the normally developed D2. 92 PEASE: First instal' Jarvie Vo1.14: no.2

On the meso- and metathorax (T-2 and T-3) the dorsal group is borne on a single chalaza or scolus in all Saturniidre. On the abdominal segments D 1 is antero-mesad of D2 and is usually on a chalaza. D 1 is always present on A-I to A-9 but may be fused on A-8 across the dorsomeson, in which case it is fl.anked on either side laterocaudad by D2 (Fig. IS). D2 is present on A-I to A-9 in the H emileucinre, Citheroniinre, and Rhescyntidinre but is fused on the dorsomeson of A-9 (Fig'!8). The Saturniinre may have D2 COI1- spicuous on all abdominal segments (Saturnia - Fig.22), reduced to a weak bristle (A elias - Fig.23), or missing on A-9 and conspicuous on the other abdominal segments (Hyalophora, Samia - Fig.24). The SD group consists of two setre below the D group. SDI and SD2 ·are both tactile on the thoracic segments and are borne on fused chalazre. On abdominal segments, SD2 is prespiracular and microscopic. It usually looks like a small puncture when visible at all. SD! is borne on a chalaza and is similar to abdominal Dl. The lateral group (L) is subspimcular on the abdomen and prespiracular on the prothorax. It consists of two setre (L 1 and L2) on T -1 and A-I to A-8. Only Ll is present on T-2 and T-3 although it is usually specialized in the same manner as LIon the abdomen. In the Saturniinre, LI is a well de veloped scolus on all segments except A-9, while L2 is of ,primitive form occurring caudad to LIon A-I to A-8 (Fig.! S). On the pro thorax L2 is mixed with the secondary setre of the lateral scolus (LI), but it can often be identified by its thinner more fragile appearance. In subfamilies other than the Saturniinre, LI and L2 may be borne on the same chalaza at equal heights (Eacles imperialis on A-I to A-7 - Fig.7), on different chalazre (R hescyntis meander - Fig.8), or on the same chalaza with L2 proj ecting caudad at halfmast (A utomeris io - Fig.6). L2 is sometimes inserted slightly ventrad of L2 on A-I to A-6 and slightly dorsad of L2 on A-7 and A-8. E. imperialis and N eocarnegia basirei have L2 projecting caudad from the base of L! on T-! and A-8. Also there are one to three secondary setre on L of T-1 in these species. The subventral group (SV) normally consists of two setre on T-! and A-3 to A-6, one seta on T-2 and T-3, one or two setre on A-I, A-2, A-7, A-8, and one seta on A-9. The group is situated just above the true legs on the thoracic segments. If more than the allotted number of setre occur, there is usually a larger number on T-1 than on T-2 and T-3. The Saturniinre have at least two subventral setre on all thoracic segments arranged in a more or less horizontal line (Fig.S). SV is a scolus on T-I in Rothschildia. The Citheroniinre, Rhescyntidinre, and Hemileucinre have two setre on T-1 and only one on T-2 and T-3. On the proleg-bearing abdominal segments, the SV are primitive setre borne on the distal part of the proIeg, one lateral and one anterior. In some Saturniinre one or more setre are arrayed horizon tally between the sclerotized plate bearing the secondary setre on the prolegs of A-3 to A-6 and the body (Fig.36). None of the species which lacked secondary setre had SV1 and SV2 in this position. Therefore, SVI and SV2 are probably mixed with the secondary setre. SATURNIIDlE PLATE 1

2 3 4

Dl ~,/ ){k) SDI I~ ~ 0 lOl ""I(

Ll 2J ILl

t--~SVI SV 2 ,/('flJJ/:'-./..1J, VI ,

5 6 7

SOl

Ll Ll ~\ SVI SVI 1 VI VI 12 S 10 II

First thoracic segment (T-1): fig. 1 - Automeris io; fig. 2 - Dryocampa rubi cunda; fig. 3 - Antheuea polyphemus; fig. 4 - Actias luna. Second thoracic segment (T-2): fig. 5 -- Hyalophora cecropia. Fourth abdominal segment (A-4): fig. 6 - Automeris ;0; fig. 7 - Eades imperialis; fig. 8 - Rhescyntis meander; fig. 9 - Samia cynthia. Eighth abdominal segment (A-8): fig. 10 - Hemileuca maia; fig. 11 - D. rubicunda; fig. 12 - Syssphinx heiligbrodti. 94 PEASE: First instar larv

On abdominal segments A-l, A-2, A-7, and A-S, the number of sub ventr.al setiP is variable. Uusually there are two setiP arranged vertically on the first two abdominal segments. A third seta sometimes appears between the two. Specimens from the same batch of eggs have differed in the number of sctiP which they possess in this group even from one side of the abdomen to the other. Except for SVI on A-I, A-2, A-7, A-S, and A-9, the subventral setiP are primitive. SVI on some or all of these segments may be on a chalaza and follow the modification of other setiP of the species under consideration. I n some H em ileuciniP SVI of A-7 and A-9 are on chalaziP while the chalaziP of A-8 are much reduced or absent. J n general, the instability of the sub ventral setiP on segments without pfolegs impairs their usefulness as taxonomic characters. However, the larger Ilumber of setiP ill this group on the thoracic segments of the Saturniime in comparison with other sub:families is a constant character. There is some question as to whether a lateral or a subventral seta occurs all the ninth abdominal segment (A-9) in the SaturniidiP. The setiP on A-9 are arranged in a more or less vertical array unlike other abdominal segments. The three most dorsal setiP (two in some SaturniiniP) are easily identified as the two (or olle) members of the dorsal group (Dl and D2) and the tactile seta of the subdorsal group (SD1). The seta close to the ventromeson is obviously ,a member of the ventral group (V1). The HemileucilliP (Fig. 16) possess olle other seta situated below the level of the lateral group on other segments. Either the lateral or the subventral group is missing. The seta and chalaza are similar to the subventral group of A-7 in some species, so the seta is probably SVl. The SaturniiniP (Fig.22) have two setiP ill this area, both of primitive form. A specimen of Hyalophora cecropia was found in which both setiP were present on the left side of A-9, but only the outer one occu rred on the right side. This suggests that both setiP are members of the S11 bventral group in the SaturniiniP with the lower seta secondary. The CitheroniiniP and RhescyntidiniP also have two setiP, but their form varies greatly. Syssphinx hciligbrodti (Fig.IS) and Dryocampa rubicunda (Fig. In have both setiP unmodified. However, the outer seta is larger, has a more prominent chalaza, and is level with L of A-8 or above it. In contrast the lower seta of E. imperialis (Fig.20) and Citheronia is more prominent and resembles LI of other abdominal segments. The other seta is always small in comparison. Although the size relationship varies, the position of the two setiP is very nearly the same in Syssphinx, Dryocampa, Eacles, and Citheronia. The higher seta of Rhescyntis meander (Fig.21) has the saw-shaped structure peculim to most setiP on the upper two-thirds of the body in this species, but the lower seta is of primitive form. A probable interpretation is that the lateral group is typically absent on A-9 of the SaturniidiP with the exception of the CitheroniiniP and perhllips the RhescyntidiniP. Since A-9 is smaller than the other abdominal segments, the loss of Ll may have been due to crowding of the setiP and to the increased flexibility of the segment which would result from a more spacious arrange- SATURNIIDJE PLATE 2

D1 ,~/

fit· (ri"ght)~ ! Ol

''''''SOl ~l SOl W

I ~ L1 ~, SV ,~ Ll

sv VI .- VI Al' 14 13

Ol ""~

SOl I ", ·t~ ~

L? "'--- SV Vl hl 19 19

SV ,J 23 VI 24

Eighth abdominal segment (cont.): fig. 13 - Eades imperialis; fig. 14 - .I1n therd!a polyphemus; fig. 15 - .11 etias luna. Ninth abdominal segment (A-9): fig. 16 Hemileuca maia; fig. 17 - Dryocampa rubieunda; fig. 18 _. SYSJphinx heiligbrodti; fig. 19 - Citheronia regalis; fig. 20 - E. imperialis; fig. 21 - Rheseyntis meander; fig. 22 - Saturnia pa'lJonia; fig. 23 -.11 etias luna; fig. 24 -- Hyalophora cecropia. 96 PEASE: First instar larva! Vo1.14: no.2 ment. Development .of a subventral chalaza as in Eades, Citheronia, and A utomeris with a corresponding loss of the lateral seta would serve to protect the larva's flank and to eliminate crowding. Numerous secondary setre on nearby chalazre and on the anal prolegs in the Satumiinre may be sufficient protection without modification of the subventral setre. The ventral seta VI is posterior to the thoracic legs on T-I to T-3. It is usually difficult to detect. On A-I and A-2 VI is mesad of the subventral setre. I t is on the inner side of the prolegs of A-3 to A-6 and near the meson on A-7 to A-9. On A-8 it is often nearer the meson than on A-7 and A-9. The tenth abdominal segment in its probable primitive form (Hemi leucinre) bears five setre on the suranal plate, five on the lateral sclerite of the .proleg, one seta on the anterior of the proleg, and three stubby setre on the mesal side of the anal pro leg (Fig.25). There is a tendency towards fusion of the three most anterior setre on the suranal plate. All setre on this plate are separate in Rhescyntis meander (Rhescyntidinre) and in Dryocampa and A nisola (Citheroniinre). Progressive fusion is clearly indicated by comparison of Syssphinx heiligbrodti (Fig.28), Cilheronia regalis (Fig.29), and Eacles imperialis (Fig.30). In the first of these, the three setre are fused only at the base, in C. regalis they are borne well up on the chalaza, and in E. im perialis a secondary seta or two are present. Saturniinre have a scolus on the suranaI plate with two or three setre inserted behind it (Fig.33). Secondary setre, when present, are usually limited to the lateral plates of the prolegs and to the chalazre of the primary setre. All Satumiinre have sec ondary setre on the more prominent chalazre. New World genera may have thorny cuticular eruptions of the cuticle of the chal,azre but usually have no secondary setre on them. Earles has extra setre on the chalaza L of T-I and the fused chalazre of the suranal plate. Comparison of H emileuca, A utomeris, and H yalophora cecropia might suggest that the secondary setre of the Satur niinre, which are mixed with and inseparable from the primary setre, have de veloped directly from the cuticular processes of the Hemileucinre. These range from the tiny bristles of H emileuca to the conspicuous spines in A utomeris. That this is not the case is indicated by the fact that some genera of the Sa turniinre (Saturnia and Calomturnia) lack fusion of Dl on A8, and all have D2 of A-9 unfused. These setre are almost always fused on the dorsomeson in New World species (exceptions are Dryocampa and A nisola which have only D2 of A-9 fused). In A glia tau D 1 is fused on A-8, but because of the size of the chalazre on A-9 it is not certain whether they were once fused or whether they merely cover more surface of the dorsum and hence appear to approach fusion. A series of specimens of H emileuca maia from Long Island may shed a little light on the method of development of secondary setre. In these, extra tactile setre occur on the dorsum of the mesothoracic to eighth abdominal seg ments and tend to displace the microscopic seta MXDI which is lateroanterior to Dl (Fig.48). Three times an extra seta was also found near D2. In one larva, both MXDl and the tactile seta are present anterior to Dl (Fig.51). SATURNIIDJE PLATE 3

26 27

Last abdominal segment: fig. 25 - Automeris io - dorsal plate, lateral aspect of proleg and ventral view (half only); fig. 26 - Eacles imperialis - lateral plate of proleg; fig. 27 - N eocarnegia basirei - lateral plate of pro leg. Dorsal plate: fig. 28 - Syssphinx heiligbrodti; fig. 29 - Citheronia regalis; fig. 30 - E. imperialis; fig. 31 - N. basirei; fig. 32 - Rhescyntis meander; fig. 33 - Samia cynthia; fig. 34 - A glia tau. PLATE 4 SATURNIIDlE

35 36

39 38

:'-bdominal prolegs (A-3)· r . C.eropza; h. fig. 37 _ Auacus att· as; 19fIg.. 35 38- ActzasH selene·., fig. 36 - H ya l ophora ce- 4;( eronza re!5.ati.s with crochet remna~ts. fi . cecropia - .anal proleg; fig. 39 - _ Rothschtldla orizaba crochets . ,g. 40 - Rhescyntzs meander crochets·' fi g. 1960 Journal of the Lepidopterists' Society 99

In all other individuals, when a t,actile seta occurs anterior to Dl, its position is close to where lVIXD 1 would normally be, and lVIXD 1 is not visible. In view of the presence and proximity of both l\1XD 1 and the tactile seta on one specimen, it is not certain that this tactile seta represents a mutation of the microscopic seta. The occurrence of the extra tactile seta was not con stant from segment to segment nor even symmetrical from left to right. On the same specimens, there is a tendency for the chalazGe D2 of A-9, which are fuseo on the dorsomeson, to separate and fuse with Dl. The tactile seta in some instances even migrated part way up the chalaza of D1 so that the structure began to resemble the fused D group of the thoracic segments (Fig. 50). J t is interesting to note that Pseudohazis has three setGe rising from chalazGe XD, SD on T-1, and SD on T-2 and T-3. This seems to be con stant. PACKARD (1914) figures first instar larvGe of Pseudohazis with three forked chalazGe. Related species have only two setre on these chalazGe. The source of the third seta is not clear. The secondary tactile setre of the Saturniinre may have appeared by a process of random mutation, with selection collecting the setre on the chalazGe. It may be s;gnificant that the setGe sometimes migr,ated up the stem of the chalaza in some of the Hernileuca rnaia. [See the chat,rt below for a com plete list of these setGe. J Another explanation would be that the secondary setGe of the SaturniinGe arose by a lengthening of cuticular processes similar to the development of the processes indioated by comparison of H ernileuca and A utorneris. As ment;oned above, the Satu rniinGe could not arise from the H emileucinre di rectIy.

Hemileuw maia - distribution of aberrant MXD1 setre on 5 specimens from West Hampton, Long Island, New York, ova collected by S. A. HESSEL.

TYPE OF SETA ON SUCCESSIVE SEGMENTS 1 SPECIMEN IT-2 T-3 A-l A-2 A~3 A-4 A-5 A-6 A-7 A-8 A-9 - - - - - #1 LEFT M M M M M M M M T M? T3 RIGHT M M M T M T M T T T M #2 LEFT M? M M? M T T2 M M2 T M? T RIGHT M? M M M M2 T2 T M M2 M? TfD #3 LEFT M M M M M M M M M M M RIGHT M M M M M M M M M M M #4 LEFT M? M T M M T M M T T M RIGHT M? M TfD TfD M M TfD T T M M +M #5 LEFT M TfD T T T T T T T T TfD RIGHT M T TfD T TfD T T T TfD T TfD

1 Symbols: M = microscopic; TfD = tactile seta fused to D1; T = tactile. 2 Dz double. II # 1 has no fusion of D2 on dorsomeson of A-9. PLATE SATURNIIDlE

44 45

~HEAD ) ",IL

Dl ,,' r I MWFLJ~", L_8 J 48 49 50 51

Dorsal set", (D) of second thoracic segment (T-2): fig. 42 - Hemileuca maia; fig. 43 - A lltomeris io; fig. 44 - Citheronia regalis; fig. 45 - Syssphinx heilig brodti; fig. 46 - A. io showing position of eversible gland on first abdominal segment (A-1). Aberrant set::e of Hemilellca maia : fig. 48 - normal left side A-2 of specimen #1; fig. 49 - MXD1 abnormal right side A-2 specimen #1; fig. 50 - extra set::e associated with D1 and MXDl apparently missing on right side A-1 specimen #5; fig. 51 - extra seta associated with Dl and MXDl present on right side A-2 specimen #4. 1960 Journal of the Lepidopterists' Society 101

A glia is unique among the species examined in that it possesses a lengthy XD group on T-1 and D group on T-3, while T-2 has a much smaller D-chalaza bearing two long and two shorter setre. Several setre are behind this chal,aza on the segment. It is probable that the two long setre represent Dl and D2, which are fused on T-1 and T-3. There are a few secondary setre scattered over the body, and eruptions of cuticle on the long chalazre of T-1, T-2, and A-8 bear single secondary setre. Aglia also has a remarkable chalaza projecting caudally on the dorsomeson of the tenth abdominal seg ment (Fig.34).

CROCHETS

The most general arrangement of crochets seems to be a single series of crochets of similar size on the inner side of the distal part of each proleg. The embedded ends are distinctly bent or hooked as well as the free ends of the crochets except in the Saturniinre, which have the embedded ends blunt. When the crochets are deeply set in the fleshy pad (spatula) on the proleg, the connections between the ends are obscured and there is an appearance of two rows of crochets where only one occurs, as in Rheseyntis meander (Fig.40). Crochet remnants, from what may once have been an outer row, are found in some specimens of Citheronia regalis and Eacles imperialis (Fig.39). N at all specimens have them. In the Saturniinre and in Citheronia, Eacles, and Syssphinx of the Citheroniinre, the crochets in the middle of the series are shortened forming a more or less C-shaped pattern (Fig.41). The number of crochets seems to be distinctive, as the following counts for Saturniinre show:

A nthercea, A etias, Calosaturnia 18 or more Saturnia 15 - 18 Hyalophora, Samia 13 -16 Rothsehildia 10 -12

Counts apply to prolegs on the third to sixth abdominal segments. A larger number of crochets always appears to the anal prolegs. The number of crochets may be related to the size of the larva, at least in some of the New WorId forms. Citheronia, EacleJ, and Rheseyntis me ander are large and have at least 20 on each segment, while the small Dryo campa rubicunda has 7 to 9 crochets, and the Hemileucinre have 6 to 9. A ttacus atlas, however, has only 13 to 16 crochets, as do H yalophora and Samia.

EVOLUTION AND TAXONOMIC VALUE OF LARVLE

Characters in the immature stages of Lepidoptera have long been used for aid in defining taxonomic groups. First instar larva.:, in particular, show less variation within taxa than adults. Species within genera may be almost identicaL 102 PEASE: First instal' larvre Vo1.14: no.2

Because of the almost cataclysmic changes which take place during meta morphosis, speculation is justified as to whether larva':, including the first instal', could diverge faster than their imagines in the course of evolution. This would seem possible, since in Lepidoptera most external structures of the imago do not develop from external larval structures but instead arise at the end of the larval period from small, previously quiescent groups of cells, the "imaginal discs." Larval-specific selective factors could not affect them nearly as much as the larval structures. Predators and parasites are examples of SLlch selective factors. Many are particular as to the stage (egg, larval instar, pupa, or adult) which they attack but not as particuIar about the species (HOWARD and WILLISTON in SCUDDER, 1889). Since immature and mature stages need not occur at the same season, the effects of climate may differ. The very great mortHlity which occu 1'5 between oviposition and pupal eclosion and the relatively long duration of this period in most species of Lepidoptera, indicates that the brunt of natural selection (aside from cou rtship recognition factors) is borne by the immatu re stages. For example, in a quantitative study of natuml populations of Phlegethontius sextus (lohan.) and P. quinquemaculatus (Haw.) (Sphingida,) LAWSON (1959) found 98 per cent mortality in larval stages alone. Yet, species differences are usually assumed to be greater in adults than larva'. A model which might result in larval divergence follows. Suppose that some selective factor was focused on larva' of several species but affected the imagines not at all. Random variation could remain the same for individuals in all stages, but since selection was concentrated on larva', net evolution would be greater in larval characters than in those of the adult. It is hardly to be expected that all species would adapt in the same way. Some would become more unlike as a result of selection. Meanwhile, no adaptation to tllis factor has been required of the adult. Thus, it seems possible that larval dif ferences could accumulate faster than those in adult structures. Species could not evolve solely by larval ad,aptation since the sexually mature stages must be reproductively isolated. Thus, for pc>pulations of the same species which were geographically isolated and had evolved different larval characters, the removal of spatial barriers would at first permit interbreeding with resulting larval polymorphism. A behavioral difference in the imago, however, might serve to isolate re united forms although they retained similar imaginal morphology. To a tax onomist looking at museum specimens, the adults would appear similar but the larv~ different. Eventually, the imagines would probably become more unlike as selective factors acted upon them more strongly than on the larva', their evolutionary divergence overtaking that of the immatures. The following examples may make this more convincing. A favorite be havioral mechanism for isolating species in the Saturniida' is the time of day or night during which a female will release the scent which attracts males. The time is characteristically different for each species. Fortunately for tax onomists, adults of these moths usually have conspicuous differences. But, in the Notodontid~, the adults of the genus Datana are difficult to separate al- 1960 Journal of the Lepidopterists' Society 103

though mature larv::e can be identified at a glance. Sibling species such as Erynnis {ucilius Scud. & Burg., E. persius Scud., and E. baptisice Forbes (Hes periid::e) have different food-plants, but adults are difficult or impossible to determine in unlabelled dried specimens even from genitalia. A conspicuous color difference makes separation of the first instar larva' of two of the species a simple matter. First instar larv::e of E. baptisice are orange while those of E. lucilius are pale greenish white. First instar larva' should be particularly helpful in taxonomic studies either (1) when morphology of the imagines differs greatly but the larva' retain similar characters, or (2) when larva' have changed and the mature stages have not diverged greatly. Each requires evolutionary conservatism in one stage and divergence in another. The majority of cases fall into the first category. However, a classic example of dissimilar larva' but superficially similar adults is that of A utomeris (Hemileucina') and the Saturniina'. Until MOSHER (1914) classed A utomeris with the Hemileucina' on the basis of pupal characters and FRACKER (1929) reached the same conclusion on larval characters, the genus was often placed in the Saturniina'. Characters have since been found in the adult for placing the genus correctly. In passing, it should be noted that the seta' are quite homogeneous in the Hemileucina' but that there is a diversity of types in the Citheroniina' and Rhescyntidina'. Tn the first group the larva' have stinging seta', and larval evolution may have proceeded along physiological lines. In the latter groups the product of evolution is more readily seen as the result of set,al modification.

KEY TO FIRST INSTAR LARVAE OF SATURNIIDlE The key was constructed from the following species, from North America unless a locality is noted. All specimens are in the larval collection at Yale University. HEMILEUCIN1E: Automeris coresus Bdv. (Argentina), A. io Fabr., A . pam ina Neum., Coloradia pandora Blake, Dirphia baroma Schaus (Brasil), D. curitiba Draudt (Brasil), D. epiolina Felder (Brasil), H emi leuca maia Drury, H. neumoegeni Hy. Edw., H. nevadensis Stretch, Hylesia nigricans Berg(Argent;na), Pseudohazis spp; CITHERONTTN1E: Syssphinx (Bouvierina) heiligbrodti Harvey, A deloneivaia apicalis Bouvier (Brasil), A nisota oslari Roths., Dryocampa rubicunda Fabr., Cit heron;a brisottii Bdv. (Argentina). C. regalis Fabr., Eaeles imperialis Drury, N eocarnegia basirei Schaus; RHESCYNTIDIN1E: Rhescyntis (Arsenura) meander Walker (Brasil) ; SATURNIIN1E: Actias luna L., A. selene Hiibner (India), An thercea polyphemus Cramer, A ttaws atlas L. (Borneo), Calosaturnia waltero rUm Hogue & Johnson, Dictyoploca japonica Moore (Japan), H yalophora (H.) cecropia L., H. (H.) euryalus Bdv., H. (Callosamia) anguli/era Walk er, H. (C.) carolina Jones, H. (C.) promethea Drury, Rothschildia orizaba West., Rhodinia /ugax Butler (] apan) , Saturnia (S.) pavonia L. (Germany), Samia cynthia L.; AGLIIN1E: Aglia tau L. (Germany). The Brasilian larva' were preserved by F. PLAUMANN, those from Argentina by]. FORSTER, those from Germany by]. REICHEL, and those from India, Japan, Borneo by C. L. REMINGTON. The nomenclature largely follows MICHENER (1952). 104 PEASE: First instar larvx Vo1.14: no.2

Notes:

1. Descriptions are for one half of the body, i.e. reference to two setre would mean the larva actually possessed four, with two arranged symmetric ally on each side. 2. Whenever the word "fused" is used, it applies to the chalazre of the setre, i.e. aDl fused on dorsomeson" means that the chalazre of the first dor sal seta from each side of the body are united so that the two set~ now arise from a common base. 3. Segments are numbered posteriorly T-l , T -2, T-3 for the three thoracic segments and A-I to A-tO for the abdominal segments.

THE KEY

1. Pro- and metathorax (T-1 and T-3) with dorsal chalazre much longer than those of mesothorax (T-2); dorsal setre of T-2 short, bearing 4 branches with 2 of these longer than the others; chalaza of dorsal seta D1 of abdominal segment eight (A-8) fused on dorsomeson; no fusion on A-9; last abdominal segment (A- 10) with a conspicuous posteriorly projecting chalaza on dorsomeson (Fig. 34); elongated chalazre have numerous thorny projections of cuticle usually bearing a secondary seta; some secondary setre on body, lateral plates of prolegs, and anal proleg ...... Subfamily AGLIINlE (Aglia tau) Chalazx of T-1 and T-3 never prolonged without similar extension of chalazx of T-2; A-10 never with posteriorly projecting chalaza on dorsomeson; if cuticle of chalazx is erupted w,ith thorny projections, secondary setre a re usually absent from their tips; secondary setre, if present, usually confined to the lateral plates of the prolegs (short hairlike setre on the elongated chalazre in SYSJ'phinx) ...... 2

2. Scoli (usually XD, SD, L, D) on thoracic and abdominal segments bear 5-12 setre of subequal length usually attached near the top (Fig. 5); dorsal scali on A-9 never fused on dorsomeson; second dorsal seta (D2) of A-9 often absent; scoli suhequal in height or at least none several times as long as others; anal prolegs with as many as 18 setre on lateral sclerotized plate; second lateral seta (L2) on prothorax (T-1) often not distinguishable from secondary setre of scolus Ll; on A-1 to A-8 second lateral seta (L2) is of primitive form and separated from secondary setre of scolus L1 (Fig.9). (Subfamily SATURNIINlE) ...... 6 Chalazre usually bearing only one or two primary setre at the top; some times 4-6 shorter processes around the setre; second dorsal seta (D2) always present on A-9, fused on dorsomeson and borne on a chalaza (Fig. 16) ; some chalazre may he much longer than homologous chalazre on different segments, particularly those on the thorax and A-8 and A-9; anal prolegs with three setre mesad, one anterior, and five on lateral sci erotized plate (Fig. 25); primitive lateral seta (L2) on T-1 present and projecting caudad from the base or near the base of Ll; L2 may rise from chalaza of L1 on A-1 to A-8 ...... 3

3. T-2 with chalaza of dorsal seta (D) several times as long as other thoracic chalazre; no fusion on dorsomeson of A-8 (Fig.ll). (Some CITHERONIINJE) ...... Anisota, Dryocampa. D on T-2 not the only prolonged thoracic chalaza; D1 fused on dorsomeson of A-8 _...... _...... 4 1960 Journal of the Lepidopterists' Society 105

4. Chalazre of dorsal (D) and subdorsal (SD) setre of T-2 and T-3 and first dorsal seta (Dl) of A-s at least twice as long as chalazre on A-I to A-7, A-9 and A-tO; chalazre may have thorny cuticular projections; some seta; of suranal plate on A-I0 usually borne on prominent chalazre (Figs. 2S to 31); primitive setre on posterior edge of cervical shield (Dl, D2) on T-1 shorter than chalazre of D on T-2; no eversible glands on A-I and A-7 ______.. ______.. ______5 Chalazre of thoracic setre subequal to those of abdomen; all chalazre without cuticular eruptions except at the top surrounding the primary selre; chalaza; of setre on suranal plate inconspicuous; primitive setre on posterior edge of cervical shield (Dl, D2) usually as long as chalazre of D on T-2; eversi.hle g lands often visible behind spiracle on A-I and A-7 (Fig. 46) ______14

5. Chalazre granulated without prominent cuticular thorns; many setre barbed and flattened giving appearance of a doubl e -~dged saw; subventral (SVI and SV2) and ventral (VI) setre of A-3 to A-6 without this modification; only one seta on the lateral plate on A-I0 has this shape; double-hooked crochets on prolegs deeply embedded in spatula giving the illusion of two rows; lateral setre (Ll and L2) rising from separate chalazre on A-I to A-S. ______Subfamily RHESCYNTIDINA~ (Rhescyntis meander) Chalazre with cuticular thorns; setre relatively smooth; crochets shallowly embedded in spatula and obviously composed of a single row with occasional remnants (3- 4) of an outer row; usually three or more setre of the sur anal plate borne on one chalaza (Figs. 2S and 29) ; Ll and L2 with chalazre at least partly fused on A-I to A-S. (Suhfamily CITHERONIINlE) ___ . __ __ . ______20

6. Only primary setre (SVl, SV2, VI) present on prolegs of A-3 to A-6; secondary setre occur on the anal prolegs; D-2 usually present on A-9 (Figs. 22, 35) ______7 All prolegs have secondary setre on the lateral sclerotized plates (making a total of 9-12 setre on prolegs of A -3 to A-6) ; D2 never present on A-9 (Figs. 24, 36) ____ 10

7. Chalazre of DIan A-S entirely separate; D2 a conspicuous seta on all abdominal segments ______.. ______.. _____ S

Chalazre of Dl on A-S partially or wholly fused on dorsomeson; D2 may be missing on A-9 ______.. __ .. ______.. __ .... ______.. ____ .. __ .. ______.. _____ 9

8_ Height of SD and D scali less than twice width; XD-SD of T-l present on anterior edge of cervical shield as a continuous band of setre ____ Saturnia, Dictyoploca Height of SD and D scali greater than twice width; XD-SD of T-l are two separate groups of setre with prominent chalaza; ___ __ ...... ______Calosaturnia, Caligula

9. Secondary setre of D and T-2, T-3 and abdominal segments recurved with tips pointing caudad; width of L scolus on T-l less than half the width of the segment; XD and SD on T -1 separate ______.. ______.______Rhodinia fugax Secondary seta; of D and SD straight, pointing in various directions; width of L scolus on T-1 more than half the width of the segment ; XD and SD on T-1 partly or entirely fused; Dl on A-8 fused on dorsomeson (Fig. 4) ______./1 ctias

10. Secondary seta; on prolegs of A-3 to A-6 arranged on both proximal and distal

parts of scI erotized plate (Fig. 37) ______.. ______00 ______Attacus atlas Secondary setre on prolegs of A-3 to A-6 arranged on distal part of sclerotized p I ate on Iy (Fig. 36) ______.. ______11 106 PEASE: First instar larva: Vo1.14: no.2

11. Scali XD, SD of T-1 ~nd D1 of A-8 fused at base only (Fig.3) ____ .. __ .. __ AnlherO!a Scali XD, SD of T-1 separate; D1 on A-8 completely fused on dorsomeson ______12

12. SV group on T-1 is a scolus with more than 3 seta:; on head capsule a light colored area appears on each side of the epicranium; 10-12 crochets on A-3 to A-6 ______Rothschildia

SV group on T-1 with at most 3 set:e; no light colored area on epicranium of head capsule (may be light colored elsewhere) ; 13-19 crochets on A-3 to A-6 ______13

13. Body appears checkered due to dark areas between pairs of adjacent scoli (Fig. 9) ______Samia

Body with transverse bands of color or unicolorous but not checkered ____ Hyalophora a. Head and body unicolorous ______Subgenus Hyalophora

b. Head capsule bicolored; body with transverse dorsal stripes ______Sub gen us Call osam ia

14. Chalaz:e with tiny processes (4-6) at tip which are less than one-tenth the length of primary set:e on the chalaz:e (Fig. 42) ______15

Chalaz:e with longer processes (4-6) at tip which are one-half to one fifth as long as the primary set:e (Fig. 43) ______19

15. Scali on anterior edge of cervical shield (SD and XD) of T-1 and subdorsal scali (SD) of T-2 and T-3 three-pronged at top with a seta on each prong ______Pseudohazis

SD, XD of T-1 and SD of T-2 and T-3 two-pronged bearing two seta: __ _ 16

16. SV chalaz:e on A-7, A-8, and A-9 subequal in height ______17 SV chalaza: on A-7, A-8, and A-9 not all subequal in height ______18

17. Eversible glands behind spiracle on A-1 and A-7 conspicuous ______Dirphia curitiba Eversible glands behind spiracle inconspicuous ______D. baroma, D. epiolina

18. Four longitudinal series of light colored dashes running from T-2 to A-9 and situated between rows of homologous groups of set:e; the dorsal and subdorsal series more conspicuous than the others; SV seta on A-7 with large chalaza while SV chalaz:e on A-8 and A-9 are reduced or wanting ______Coloradia Body without longitudinal light colored stripes; SV chalaz:e on A-7 and A-9 of subequal height; A-8 with SV chalaza reduced or wanting (Fig.10) __ Hemileuca

19. Chalaz:e about onc half the dorsoventral diameter of the body; fused chalaz:e with only a slight fork below the insertion of the primary set:e; eversible glands in- can s p icuous ______H yl esia

Chalaz:e equal to or greater in length than the dorsoventral diameter of the body; tused chalaz:e with conspicuous fork below the insertion of primary set:e; ever- SIble glands prominent behind spiracle on A-l and A-7 ______Automeris 1960 Journal of the Lepidopteri5t5' Society 107

20. Elongate chalaza: not swollen at top; DIan T-l and D2 on A-I to A-8 short, thickened and bullet shaped; primitive lateral seta (L2) on T-l and A-8 usually projects caudad from base of L chalaza (Fig. 13 ) ; lateral scolus (L) on T-l with 1 to 3 secondary seta:; SV chalaza on A-9 prominent (Fig.20) ...... 21 E longate chalaza: swollen at apex; D1 on T-1 and D2 on A-1 to A-8 longer and bristle-shaped; L2 on T-1 and A-8 usually at top of L chalaza (Fig.12); L on T-1 with no secondary seta:; SV on A-9 relatively inconspicuous (Figs.18 and 19) ...... 22

21. One or two secondary seta: on prolegs of A-3 to A-6; some fusion on lateral plate of proleg on A-10 (Fig. 31) ...... Neorarnegia ba5irei No secondary seta: on prolegs of A-3 to A-6; chalaza: separate on lateral plate of anal proleg (Fig. 30) ...... Eades i11lperiali5

22. XD at least as large as the most prominent structures on T-2 and T-3 and moved lateral to a level between D and SD on '1'-2; SD on '1'.·1 less than one-tenth as large as XD and severely crowded ...... /J delonei'Vaia apicali5 XD not as large as the structures on T-2 and at nearly the same level as D on T-2; XD on T-1 may be subequal or several times as long as SD ...... 23

23. Hairlike seta: along the entire length of elongated chalaza: (D, SD on T-2 and T-3, D1 on A-8) ; prima ry seta: on fused chalaza: parallel to each other; XD and SD on cervical plate subequal and reduced; thorny processes on D1, SD, and L of A-1 to A-7 only at base of chalaza: (Figs. 12, 18, 45) ...... SYHphinx Ha,irlike seta: lacking on all chalaza: ; primary seta: on fused chalaza: wi'dely diver gent forming acute or obtuse angle; XD several times as long as SD on T-1; thorns on D1, SD, L of A-1 to A-7 along the whole length of chalaza: (Figs. 19, 44) ...... Citheronia

RECAPITULATION OF SIMILARITIES AND DIFFERENCES

There are two clearly separated groups in the family Saturniid::e. One includes the primarily Old World subfamily Saturniid::e. The first instal' larv::e of this group have numerous secondary set::e on wartlike processes (scoli). Each scolus with its secondary set::e is homologous to one, two, or four primary set::e. Secondary set::e also occur on some or all of the prolegs. There are tendencies toward fusion of scali in the middle of the dorsum of the eighth abdominal segment but never on the ninth abdominal segment where the second dorsal seta (not a scolus) tends to be lost. The other group includes the New World subfamilies Citheroniin::e, He mileucin::e, and Rhescyntidin::e. Scoli ,and secondary set::e rarely occur. Set::e and the chalaz::e supporting them on the thoracic segments and abdominal segments eight and nine are often quite different in size and form from those on other segments. The first set of dorsal set::e on the eighth abdominal seg ment and the second set of dorsal set::e on the ninth abdominal segment are usually fused in the middle of the dorsum on both segments. The Agliin::e have numerous secondary set::e, but many of the !primary set::e can be distinguished from the secondary set::e. The first dorsal set::e are 108 PEASE: Fi rst instar 1a rv

The order of branching in MICHENER'S phylogentic tree is, from bottom to top, Eaeles and Citheronia, Syssp'hinx, A deloneivaia, Dryocampa and A ni sota, and N eocarnegia. Based on larval setre, Dryocampa ,and A nisota are separate from the rest, but whether they represent the loss of many special ized characters or a really primitive type is not certain. At the very least, the larvre suggest that these two genera belong either at the top or bottom of the Citheroniinre if not in their own subfamily. Eaeles and Neocarnegia have important similarities in the manner of branching and the shape of setre. The two genera seem at least as close as Citheronia and Eaeles. Syssphinx is distinct in having hairy chalazre. A deloneivaia has unique widely spread prothoracic chalazre. The clue to the position of A deloneivaia and Syssphinx probably lies in other species of these or ·allied genera. 110 PEASE: First instar larvre Vo1.14: no.2

There is a general trend toward fusion of setee on the last abdominal segment - Dryoeampa and A nisota with none, to A deloneivaia, Syssphinx, Citheronia, Eaeles, and N eoearnegia. A complete study of the first instar larvee of the Saturniidre may settle phylogenetic relationshi,ps precisely. It is usually no more difficult to collect first instal' larvee than it is to collect adult female moths, since oviposition readily takes place in almost any container. Preservation in alcohol or fixative is somewhat simpler than preparing adults, and a complete collection of first instar larvee of all the Saturniidee would occupy the space of only three or four museum drawers. In fact, living material of species whose larvae have never been adequately described can be purchased from commercial breeders. The inescapable conclusion is that a taxonomic collection should and easily can include samples of first instal' larvre.

SUMMARY

1. First instar larvee of the Le,pidoptera have certain primary setee which are found throughout the order. Other setee which appear in later instars or only in more specialized forms are called secondary setee. The variation of the setee and their supporting structures is useful taxonomically and phylogenetically. 2. There is a general tendency toward fusion of the supporting struc tures (chalazee) of certain groups of setee followed by fusion of whole groups particuarly on the dorsum of the thorax and eighth, ninth, and tenth ab dominal segments. As a rule, only the supporting structures fuse; the 'Primary setee remain separate although it is useful to say, for example, "the first dorsal setee are fused on the dorsomeson." 3. The evolutionarv significance of first instar larvee and the relative effects of selection on adults ,and larvee are discussed. A model is given whereby larvee might diverge faster than adults. Several examples are men tioned where larval recognition characters are better than those of adults. 4. A series of aberrant H emileuca is discussed in relation to the evolu tion of secondary setee. 5. A key to the first instar larvee is presented. 6. The Old World subfamily Saturniinee and the New World sub families Citheroniinee, Hemileucinee, Rhescyntidinee are clearly separated by larval differences. The Agliinee may be a specialized offshoot of the New World group. 7. Within the Satu rniinee, the genera A etias, Caligula, Calosaturnia, Dictyoploca, Rhodinia, and Salumia are separated from the more specialized genera Attacus, Anthercea, Hyalophora, Rothschildia, and Samia. 8. The Hemileucinee seem rather homogeneous. 1960 Journal of the Lepidopterists' Society 111

9. Within the Citheroniime, Citheronia, Eacles, and N eocarnegia are related while A deloneivaia and Syssphinx are distinct. Dryocampa and A ni sota are very similar. However, the differences which separate these two genera from the rest of the Citheroniime seem greater than those which sepa rate the Citheroniime from the other New World subfamilies.

ACKNOWLEDGEMENTS

The author is particularly grateful to Dr. C. L. REMINGTON for advice and encouragement while preparing the paper and to Dr. P. F. BELLINGER for reading and criticizing the manuscript. Many of the specimens were sup plied by F. PLAUMANN in Brasil, J. REICHEL in Germany, and F. P. SALA in California.

References

Fracker, Stanley B., 1929. The classification of lepidopterous larvx. revised. Illinois Bioi. Monographs, vo!.2, no.l : 161 pp .• 10 pis. Gerasimov. A. M .. 1935. Zur Frage der Homodynamie der Borsten von Schmetter lingsraupen. Zool. Anz. 112: 177-194. 8 figs. Hinton. H. E .• 1946. On the homology and nomenclature of the setx of lepidopterons larv:e. with some notes on the phylogeny of Lepidoptera. Trans, Royal enl. Soc. Loudon 97: 1-37. Lawson. F. R.. 1959. The natural enemies of the Hornworms on tobacco (Lepidoptera: Sphingidx). Ann. ent. Soc. Amer. 52: 741-755. Michener. Charles D .• 1952. The Satnrniid:e (Lepidoptera) of the Western Hemis phere. Bull. Amer. Mus. nat. Hist. 98: 341-400. figs.1-420. Mosher. Edna. 1914. A classification of the pupx of the Ceratocampidx and Hemi leucidx. Auu. eut. Soc. Amer. 7: 277-300. Packard, A. S., 1905. Monograph of the bombycine moths of North America, Part II. Mem. nat. Acad. Sci. (Washington) 9: 1-151. 61 pIs ...... 1914. Monograph of the bombycine moths of North America. Part III. Mem. nat. Acad. Sci. 12: pp.ix + 1-276, 503-516, pI5.1-113. Peterson. Alvah. 1948. LarVa! 0/ insects. Part I. Lepidoptera and Hymenoptera. 315 pp .• 70 pIs. Scudder. S. H., 1889. Butterflies 0/ the Eastern U. S. and Canada, vo!. 3: pp. 1869- 1924. pis. 88. 89. Schiissler, H .• 1933-1936. Lepidopterorum Catalogus, vol.l0 (partes 55, 56. 58, 65. 70, 75. 76): Saturniid:e 769 pp.; Syssphingid:e 230 pp.

Dept. of Zoology. Yale University, New Haven, Conn .• U. S. A.