Descriptions of the Nymphal Stages of Some North American Pentatomidae (Hemiptera-Heteroptera)x RUSSELL M. DKCOURSKY2 AND CHARLKS 0. ESSELBAUGH3 ABSTRACT A study of various instars is presented as an aid to (Say), Trichopcpla scmivittata (Say), Ncoitiglossa sulci- identification. The external morphological characters of jrons Stal, Peribalus limbolarius Stal, Pitcdia pcrsimilis nymphs are discussed, and a detailed description is given Horvath, Thyanta custator (Fabr.), Cosmopcpla bimacu- of each instar (with very few exceptions) of the follow- lata (Thomas), Ocbalus pugnax (Fabr.), Acrostcrnum ing 1(> species: lutschistus variolarius (P. de B.), E. hilarc (Say), Podisus maculivcntris (Say), and Pcrillus i-uschistaides (Voll.), li. tristigmns (Say), Mormidca bioculatus (Fabr.). At least one instar each of 14 of lut/cns (Fahr.), Cociuts dclius (Say), Mcncclcs inscrtus these species is illustrated. Downloaded from https://academic.oup.com/aesa/article/55/3/323/138081 by guest on 27 September 2021 There is an ever increasing' need for life history nymph is usually almost as broad as long, the greatest .studies and descriptions of immature stages in the width being across the abdomen, slightly caudad of various disciplines of Entomology. The taxonomist, the thorax. For a day or more following eclosion the the morphologist, and the economic entomologist have nymph appears truncate posteriorly due to the abdo- found that the study of immature stages often serves men's being slightly drawn up beneath. After about 24 to increase their understanding of current problems. hours the abdomen straightens out, leaving the nymph Exact and adequate descriptions of nymphal instars rather abruptly tapered posteriorly. At this stage the should prove useful in a variety of ways toward fur- nymph is broadly oval or somewhat elliptical in gen- thering our knowledge of this large family, the Pen- eral outline. Since the abdomen becomes more dis- tatomidae. Illustrations are usually a helpful adjunct tended than the other body regions in the feeding to the descriptions and so are included. 'instars, the nymph becomes pyriform in shape dur- At the beginning of the century only a few en- ing the latter part of these instars. It is proportion- tomologists recognized the need for identifying im- ately broader than the adult in the earlier instars but mature stages, Guide (1902), Kuhlgatz (1905). In gradually approaches the final form except that it is recent years, many authors have described or re- much less angular. The head is strongly declivent ferred to nymphal stages of the Hemiptera-Heterop- during the first instar but becomes less so except in tera including the Pentatomidae. Among these are those species in which this is characteristic in the DuPuis (1947), Ksselhaugh (1948), Guide (1934), adult stage. Miller (1956), Puchkova and Puchkov (1958), The pronotum is fairly well developed in the first Southwood and Leston (1959), Tullgren (1918), and instar except for the humeral angles, which are non- Weber (1930). existent. The mesonotum is not greatly differentiated There are, of course, numerous papers referring to since its distinctive characters, the mesonotal wing- nymphs of certain genera of the Pentatomoidea. Many pads and scutellum, develop only gradually during of these articles deal with applied aspects of economic the third, fourth, and fifth instars. In the early in- entomology. stars, before the development of mesonotal wing-pads There have been relatively few keys for the iden- and scutellum, the metanotum is exposed, but in later tification of nymphal stages, however Butler (1923) instars it is largely covered by these structures. In discussed nymphal characteristics of British Hemip- the fifth instar, the visible portions of the metanotum tera-Heteroptera, and Jordan (1951) presented a consist of the medial margins of the wing-pads and key to the nymphs of families based on representatives a median portion just posterior to the developing present in Germany. Leston and Scudder (1956) pub- scutellum. lished a key to the larvae of families of British Hemip- Unlike in the adult, the tergum is completely ex- tera-Heteroptera. Puchkov (1959) discussed the posed except for that portion covered by the wing- larvae and included a key to the families of Penta- pads during the final instar and it therefore furnishes tomoidea. Southwood (1956) formulated a key for a new set of recognition characters. The principal determining an individual instar of heteropterous features here are two series of rather heavily scler- larvae although he stated that it is not entirely re- otized plates, a mediodorsal series and a lateral series liable for pentatomoid larvae. along the lateral margins. Both series usually stand out against their backgrounds by color contrast, be- KXTKRNAL FEATURES ing almost invariably darker or at least with dark Pentatomid nymphs vary somewhat in outline but margins. Hart (1919) named these the median and usually are not much elongated. The newly hatched lateral plates, respectively, and there seems no reason to change the nomenclature. The number of units in 1 Accepted for publication August 14, 1961. - Department of Zoology and Entomology, University of the median series varies somewhat, due to the pres- Connecticut, Storrs. ence or absence of small vestigial ones. There are :l This paper was in preparation by the late Charles O. Essel- baugh just prior to his death, and the descriptions and illustrations three principal plates in the median series and these are in large part his work. The manuscript has been edited and revised by the senior author. are the ones usually referred to. These differ from 323 324 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA [Vol. 55 the others not only in size but they have a more def- frequently a week or 10 days between the molting of inite margin and contain also the paired openings of the first and last individuals and there may be a dif- the dorsal scent glands. The pleural ostioles of the ference of nearly 3 weeks between the minimum and adult are absent in the nymph. maximum for these instars of a given species. The first of these plates, located between the third In a very general way it can be said that the first and fourth abdominal segments, is not so well de- instar lasts about 3 or 4 days, the next three about veloped, in our species at least, as are the other two. a week each and the last about 12 days, making The other two median plates are larger, the transverse about 5 weeks in the nymphal stage. dimensions usually being about the same as those of Molting.—In common with all creatures which the first plate but the longitudinal one being greater. must undergo this ordeal, the freshly emerged in- All three contain a transverse slit or suture with an dividuals are incapable of much muscular movement. Downloaded from https://academic.oup.com/aesa/article/55/3/323/138081 by guest on 27 September 2021 opening at either end. In the case of the first plate Lacking means of protection, they are then prey to this opening consists of a simple loop, but in the many forms which might not molest them at other others the distal portion of the loop appears to have times. A given individual is often subject to attack been squeezed practically together, forming a sort not only from those which have molted and hardened of loose fold and the latter then bent cephalad to first, but also from individuals of other instars. The form a rather open hook. The last two glandular only means of protection open to the individual is to plates lie between the fourth and fifth and the fifth retire to some more or less secluded spot before and sixth tergites. molting. The lateral plates consist of eight pairs of what Another cause of mortality at this time is the mere appear to be patches lapped over the edge of the inability of the individual to completely divest itself abdomen, a pair to each of the first eight segments. of the old skin before the new one hardens. Some The name usually refers specifically to the portion die outright and others are left so crippled as to inter- on the dorsum, which is usually more or less semi- fere with feeding or other body functions. Atmos- circular but is oblong in some species. The proximity pheric humidity is very important at this time. Too of the plates to each other is determined chiefly by rapid evaporation does not give the molting nymph the extent of distention of the abdomen. sufficient time to free itself and excessive humidity The genitalia have no sex differentiation but, ac- may be conducive to attack by fungi. cording to Hart (1919), in the male the penultimate A freshly molted nymph or adult is decidedly lack- sternite is swollen and often longer at the middle than ing in pigment and is very pale, except the eyes at the ends and sometimes there is a triangular de- which are usually red. Like the nymph which has pression on the hind margin of this segment, notch- just hatched from the egg, the freshly molted one ing the swollen portion. In preserved specimens this begins darkening within a few minutes, the head, does not seem to show distinctly enough to be re- thorax, and median and lateral plates showing the liable. most pronounced change. During all the nymphal instars the number of an- A day or so before molting the nymph becomes in- tennal segments is four, or one less than in the adult. active to a considerable extent and stops feeding. At At this time the second segment is disproportionately this time it isolates itself if opportunity offers. Be- long, becoming increasingly so with each succeeding fore molting actually begins, the tarsal claws are instar.