A comparative study op the labium op COLEOPTEROUS LARVAE. by William Henry Anderson. Thesis submitted to the Faculty of the Graduate School of the University of Maryland in partial fulfillment of the requirements for the degree of Doctor of Philosophy. UMI Number: DP70062 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Dissociation Publish ng UMI DP70062 Published by ProQuest LLC (2015). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 TAELS OF CQlTTEh'TS. Page. Preface - - - - - - - - - - - 1 Introduction - - - - - - - - - - 2 I. The structure of the head capsule of coleopterous larvae - - - - - - 3 The head of Silpha sp. - - - - - - 3 The head of Chauliognathus sp. - - - - 7 The head of Ortho soma sp. - - - - - 11 II. General discussion of the insect labium - - 15 Comparison of various types of labial structure - - - - - - - - - 2 1 III. Descriptions of labia of coleopterous larvae 24 17. The tentorium of coleopterous larvae - - 54 V. Conclusion - - - - - - - - - 5 7 Abbreviations used on the figures - - - - 58 Plates I _ XI - - - - - - - - - “ 61 References - - - - - - - - - - 73 PREFACE. Herewith I wish to express my appreciation to Mr. H. E. Snodgrass of the United States Bureau of Entomology. He has "been an unfailing source of guidance and assistance, and his encouragement has been little short of inspirational. To Dr. A. Gr. Boving of the United States Rational Museum I also express deep gratification. He has helped me not only by making valued suggestions but also by identifying larvae which I collected and by loaning me representatives of families which X could not have studied otherwise. In nearly all cases the drawings were made from material dissected under a binocular. In a few instances mounts were made on microscope slides and studied with the compound microscope* INTRODUCTION. The present problem was undertaken with the idea of comparing the labia of coleopterous larvae and giving the proper connotation to the various parts and plates thereof. The naming of the divisions has been based on a study of muscle insertions and origins. It is hoped that students of systematic entomology may gain some help, either directly or indirectly, from the facts brought out in this study. The mouth parts, or organs of feeding, in some insects are directed downwards, that is the plane in which they move is vertical. Insects which move the gnathal appendages in this manner are spoken of as hypognathous. In other forms however, the head capsule is turned upwards on the neck, through approximately ninety degrees, and the mouth parts are directed forward. In this condition they move in a horizontal plane. An insect in this group is said to have a prognathous head. In order that this forward and upward rotation should not change the plane of the foramen magnum (PI. I, B, Por), modifications in the form of elongation of the posteroventral region of the head was essential. This lengthening took place at the base of the labium or by the addition of a gula to the proximal part of the labium. Thus in coleopterous larvae, which in nearly all cases have the prognathous type of head, the gula (PI. I, B, Gu) is generally well developed. 3 - - Except for the modifications brought out by the above mentioned revolution, the head capsule of coleopterous larvae conforms in general with that of a generalized insect such as the roach. THE STRUCTURE OP THE HEAD CAPSULE OP COLEOPTEROUS LARVAE. The head of Siloha sp. Siloha is an excellent subject for a morphological study of the generalised coleopterous larval head. The larvae are easily obtained in quantity and are sufficiently large to permit of ease of dissection. The head (PI. I) is robust, somewhat wider than long, the greatest width being behind the middle. In dorsal view (A) the coronal suture (cs) and the frontal sutures (fs) are readily visible and unmistakable. The epistomal suture (es), although its central portion has become lost, aids further in the delimitation of the areas of the dorsal surface of the head. In it are found the anterior tentorial pits (at), it serves to divide the area in front of the frontal sutures into the clypeus (Clp) and the frons (Fr). The clypeus and lab ram (Lin) are not united as in some forms but are clearly separated by the clypeolabral suture (els). The antennae (Ant) are comparatively long and consist of three segments. There are, on the dorsal surface of the head, four ocelli (Qc) on each side just behind the bases of the antennae, and on -4— the ventral surface there are two more ocelli (B, Oc) on either lateral margin. The postoccipital strbure (A, pos) is found along the posterior margin of the head capsule and behind it lies the rather narrow postocciput (Poc). The ventral surface of the head (B) shows the maxillae and labium to be retracted, leaving a narrow bridge between the foramen (For) and the posterior articulations of the cardines (a11). In this bridge are the posterior tentorial pits (pt) which lie in the ends of the anteriorly extended postoccipital suture (pos). Behind and between the tentorial pits is the gula (Gu), which although somewhat small, is a true example of this structure. The maxillae and the labium are seen to be united for approximately half their lengths by a large membranous area which, however, allows of separate action. Discussion of these parts is given elsewhere. In order that the relationship between the labial and hypo- pharyngeal muscles may be more readily understood, a lateral view of the labium is shown (C). In addition to the retractors of the prementum (rst) and the ventral adductors of the labium (2adlb), which are described below (Pg. 30) there are present the dorsal adductors of the labium (PI. I, C, ladlb). These arise on the base of the postmental sclerite (Pmt) very close to the ventral adductors, and insert on the base of the first prementum (iFrmt), dorsal to the ventral adductors. The retractors of the hypopharynx (E, rhphy) arise from the tentorial arms (Tent) close to their bases. This set of muscles inserts on the hypopharynx about midway between the anterior margin of the ligula (Lig) 5 - - and the mouth (lith) • The maxilla of Silpha (D) shows only a slight indication of a division "between the lacinia (Lc) and galea (Ga). Tith their rather complete fusion into one part there have "been lost the stipital flexors of these parts. However the cranial flexor of the lacinia (flee) is present. It arises on the postocciput and is a short muscle attached to a long apodeme which inserts on the inner margin of the base of the lacinia, slightly anterior to the insertion of the adductor of the stipes (adst). In the stipes (St) arise two opposing muscles, the depressor (dplp) and levator (lplp) of the palpus. The tentorial muscles of the stipes consist of a large bundle having its origin on the tentorial arm (Tent). This muscle, the adductor of the stipes (adst) inserts just within the stipes, close to its inner margin. Near the origin of the latter muscle there arises from the tentorium a muscle of the cardo, the adductor of the cardo (adcd). It inserts in the cardo on its lateral surface. Also inserting on the cardo, or more properly on an apodeme from the base of the cardo, is a short muscle the promotor of the cardo (pmcd)♦ It originates from the postgena about halfway between the cardo and the posterior angle of the head. As was stated above in the discussion of the external view of the head, the areas are well set off by sutures. The delimitation of these areas is further aided by a study of the muscles of the anterior part of the stomo&eum. The presence of the frontal ganglion -6- (E, ErGng) separates the muscles arising on the clypeus from those arising on the frons. The former insert on the stomodeum anterior to the ganglion, the latter posterior to the ganglion. In gilpha there is only one pair of muscles which arises on the clypeal region. These, the dilators of the buccal cavity (dlbc), insert on the stomodeum just posterior to the true mouth opening (Midi). The function of this pair of muscles is, of course, to enlarge the buccal cavity to admit passage of food. The anterior (idlphy) and posterior (2dlphy) dilators of the pharynx arise on the frons and insert on the dorsolateral surface of the pharynx. The anterior set attaches in very close proximity to the frontal ganglion. The posterior dilators arise somewhat behind the former and insert on the pharynx just before the brain (!Br). Between the origins of these two groups of muscles there arise the retractors of the mouth angles (rao) which insert on the posterior end of the oral branch of the suspensorial sclerite of the hypopharynx (HS). This muscle, as its name implies, serves to retract the margins of the mouth opening* The ventral muscles of the pharynx have their origin on the tentorium, but not on the same part as that from which the retractors of the hypopharynx (rhphy) originate. The ventral dilators 01 the pharynx (vdlphy) arise from a posterior extension of the tentorium, on which are also attached the ventral muscles from the prothorax. A tentorium with this posterior extension seems unique in this larva and it will be discussed in another part of the paper. The posterior labral muscle (ralrp) has been included in this figure (E) to show the relationship of its origin with that of the dorsal pharyngeal muscles. The head of Chauliognathus sp. The head of Chauliognathus viewed dorsally (PI. II, A) has the general form of a rectangle, with the two lateral margins nearly parallel but inclined slightly towards one another on the posterior half of the head. Its length, including the maxillae and palpi, is approximately one and one-half times its grestest width measured immediately behind the ocelli (A, Oc). The head capsule is not set deeply into the prothorax and the cervical membrane (Cvx) attaches close to the post­ erior margin of the head. There are no boundary markers in the form of sutures which would assist in the definite separation of the areas on the dorsal surface of the head. By a study of the pharyngeal muscles (P) however, the general region of the frons (A, Pr) is shown by the origins oi' the dilators of the pharynx (P, dlphy). The clypeus and labrum (A, Cl? + Lm) are completely fused and the clypeal margin of the head is nearly transverse, with a series of five teeth on either side. There is only one pair of ocelli (Oc). They are placed on tne lateral margins of the head capsule, immediately posterior to the bases of the antennae. The antennae (Ant) are three segmented. The second segment is slightly longer than the first. The third has become greatly