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Immature Stages of Tachinidae


Clausen (1940) discussed the immature stages of Tachinidae as follows:


The Egg.‑‑There are four general types of egg produced by the Tachinidae:


1. Macrotype.‑‑The eggs of this form have a very heavy and opaque dorsal chorion, with the ventral surface flat and the chorion thin and more or less transparent.  They differ from other types principally in size, color, the stage of development of the embryo at the time of deposition, and the manner in which hatching is accomplished.  The general form is oblong, the anterior end being very nearly as wide as the posterior. and in lateral view they are markedly arched, at times approaching the hemispherical with the ventral side flat or at times slightly concave.  A few species of Nemorilla and Gymnosoma bear a distinct marginal flange at the juncture of the flat ventral surface with the lateral areas. In size, the eggs of the different species range from 0.4 to 0.9 mm. in length, with the width varying from one‑third to two‑thirds the length.  The color is usually creamy‑ or glossy‑white at the time of deposition, later changing to a gray or light brown.  The micropylar area is usually dorsal and somewhat pigmented, though in Gymnosoma it is terminal or slightly ventral.  In a few species, the surface of the chorion bears rather minute reticulate markings. Townsend described the unusual egg of Phasiopsis floridana Tns. as asymmetrically long‑ovate, the right side straight on the middle half and the left side evenly curved, and brown in color.  It differs from those of other species, also, in revealing this coloration even before deposition.


The macrotype eggs are divided, on the basis of the manner of hatching, into two distinct groups termed "dehiscent" and "indehiscent" by Pantel.  The latter form has no special provision for hatching, which is accomplished by cutting through the thin ventral shell directly into the host body.  The eggs of Centeter, Meigenia, and Trichopoda are representative of this group.  The dehiscent eggs have a distinct seam, or line of fracture, across the anterior margin, which curves backward and somewhat dorsad; at hatching, this seam is broken, and the lid is forced upward to permit the larva to emerge into the open.  Ptychomyia, Tricholyga, and Winthemia (Fig. 209F) deposit eggs of this form. The macrotype eggs carry a quantity of mucilaginous material at the time of deposition, which fastens them securely to the body of the host.  In some species, this material may be observed in regular loops or folds on the venter of the uterine egg.


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                        Fig. 207


                           Fig. 208

      Fig. 209



2. Microtype.--This type of egg has many characters in common with the macrotype; as the name indicates, it is of minute size in relation to the body of the parent female.  One of the largest recorded is that of Chaetogaedia monticola, which measures 0.44 by 0.25 mm.  Thompson has given the measurements of a large number of eggs of this type, the great majority of which range from 0.02 to 0.2 mm. in length.  Those of Zenillia pullata and Pseudogonia cinarescens Rond. are exceptionally minute, measuring 0.027 by 0.02 mm. and 0.08 by 0.05O mm., respectively.  The majority are approximately two‑thirds as wide as long, ranging to almost circular in Phryno vetula Meig.  Townsend calculated the volume of a considerable number of eggs of this family and reported that the large macrotype egg of Gymnosoma, which is 0.9 mm. long, is approximately two thousand times the volume of the microtype egg of Z. pullata.  In general, microtype eggs are only about one‑fiftieth as large by volume as macrotype eggs deposited by females of the same size.


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                 Fig. 210

                Fig. 211

            Fig. 212


The general form of the egg is ovate, with the anterior end narrower.  In side view, the outline is somewhat semicircular, though often somewhat flattened; but in Racodineura antiqua (Fig. 207C) (Thompson, 1920b, 1928) the dorsum is in the form of an asymmetrical cone, with the summit bearing an irregular group of strongly sclerotized elevations, which are surrounded by a number of small button‑like structures, doubtfully considered to be respiratory papillae (Clausen 1940).  With reference to Otomasicera patella Tns., the egg is described as limpet‑like, with irregular concentric peripheral thickenings.  Those of many genera of Exoristinae and of Epidexia, also, are very elongated, subelliptical, and pointed at both ends; they have submembranous chorion extensions and the dorsum is black, coarsely punctate, with reticulate markings and a median longitudinal suture.


The surface markings of the eggs of other species range from a very fine punctuation to a deep pitting or reticulate marking. The heavy chorion of the dorsum ranges in color from gray to brown and to the more frequent shining black, though Townsend listed several genera in which they are yellow or even white.  In Pexopsis aprica Meig., there is a densely pigmented hemispherical process of unknown signifi­cance, at the anterior end; the egg of Sisyropa sp., which has the reticulate surface, bears also an irregular, light‑colored fringe around the margin, which is pierced with microscopic holes.  On the ventral side, the chorion of the microtype egg is thin and transparent, though in Gonia capitata (Fig. 207B) the thickening and pigmentation are only reduced ventrally and are entirely lacking only on the median line. The micropyle is clearly recognizable in the eggs of many species and occurs at the nar­rower, anterior end.  The embryo is enveloped by a tough vitelline membrane.


3. Membranous.--This type of egg is distinguished in general by its elongated form and thin transparent chorion.  In size it is minute to large, ranging from 0.2 mm., about half the length of the largest microtype egg, to equal to the macrotype eggs from equal sized females, and the length may be from three to six times the width.  The ventral surface is not flattened and therefore does not permit of close attachment, to the host or to foliage.  Its form may range from long cylindrical, with both ends evenly rounded, to markedly arched or bowed, with the ventral line straight or con­cave and the anterior end appreciably narrowed.  The micropyle is terminal and may be simple, of rosette form, or with various short processes, which are particularly noticeable on the ovarian eggs. The surface reticulations of the chorion, termed the "pneumatic apparatus" by Pantel, are often quite conspicuous, the lines being brownish in color.  These reticulations may be complete, as in Bonnetia comta (Fig. 207D), limited to the middle portion of the egg, or of uneven distribution as in Peleteria prompta Meig.


These thin‑shelled eggs hatch in the uterus of the female or almost immediately after deposition.  The few species that deposit unincubated eggs of this type inject them into the body of the host.


4. Pedicellate.--The egg of Carcelia (Fig. 207E) is placed in this group.  It has a membranous chorion and bears a slender cylindrical pedicel about 1/5th the length of the body, at the posterior end.  This stalk is expanded at its distal end into an adhesive process, by means of which it is fastened to a hair or to the integu­ment of the caterpillar body. 


First‑instar Larvae.--There are three general forms of first‑instar larvae follows:


1. Tachiniform.--The larvae included in this group are those which may bc considered as normal for the family, and they have no marked modifications in form or structure to adapt them to a specialized mode of life. as number of larvae of this type have been described in detail by Thompson (1926).  They include all those hatching from macrotype and pedicellate eggs, those which are injected into the body of the host, and finally, those from the membranous type of egg which, as fully incubated eggs or newly hatched larvae, are deposited upon tho host body or in its immediate vicinity. The latter are presumed to reach the host very quickly and consequently require no modification of the integument to protect them from desic­cation and injury.  The body is usually robust, with the cuticle colorless and trans­parent, and usually bears bands of rather minute spines on each segment, particularly at the margins, these bands being most frequently complete on the thoracic segments and predominantly ventral on the abdomen.  A few species, such as Centeter cinerea (Fig. 208A) appear to lack the spine bands entirely.  A definite adaptation for attachment to internal tissues or organs of the host is found in Anetia, Compsi8lura, Paradexodes, and some other genera.  This consists of a set of three heavily sclerotized spiracular hooks at the caudal end of the body, each of the two dorsal ones being situated immediately above a spiracle and the third on the median line somewhat below them.  The dorsal hook3 are simple and sharply curved, with the points directed cephalad, whereas the median one is double‑ or triple‑pointed and directed ventrad.  These hooks are integumentary in origin and are not a part of the spiracular structure itself, thus differing from the spiracular hooks in later instars of certain other species.  In this group is also included the vesiculate larva of Plagia trepida, which, if the adaptation were more highly developed and of more frequent occurrence, might constitute a separate type, as in the Hymenoptera.


2. Microtype larva.--These larvae, which are derived from microtype eggs that hatch within the digestive tract of the host, are of very small size and lack the various adaptations associated with a period of free life or with the necessity of penetrating n heavily chitinized host integument.  The buccopharyngeal armature usually shows a reduction and simplification.  Thompson (l924) has given detailed descrip­tions of the larvae of a large number of species, with keys for distinguishing them.  The skin is thin and colorless and without any evidence of specialization except for the transverse rows of minute spines at both margins of the body segments, those on #he abdomen usually being present only on the venter (Fig. 208E).  In Gonia capitata and various other species, the first segment bears dorsally at its anterior margin a group of I0-12 strong hooks, which are heavily pigmented.  In several species of Gonia described by Tothill, there are transverse rows of four hooks ventrally between the posterior segments, and the outer ones are connected by an internal chitinous rod.  The larvae of Racodineura antiqua, Brachychaeta spinigera Rond. and Pales pavida Meig. lack the caudal spiracles, whereas in Phryno vetula they are present but very small and probably not functional.  The spiracles arc lacking also in Exorista fimbriata Meig., and the felt chamber is short, filiform, and almost invisible.  The frequent absence of an open tracheal system in larvae of this type is correlated with their mode of life in this stage, during which they are usually embedded in some host organ.  Except for its size and its association with the microtype egg, the microtype larva has few characters to distinguish it from the tachiniform larva.


3. Planidium larva.--The essential adaptive characters of the tachinid planidium are for the purpose of protection from injury and desiccation during a more or less pro­tracted period of free life before the host is reached.  They consist of a cuticular armature of closely set polygonal sclerotized plates, or imbricated scales, covering the dorsum and pleural areas, and in some species a large portion of the venter as well, of all body segments except the last, forming a carapace.  Though most planidia have the armature in the form of scales or plates, yet in several species it is in the form of nodules or minute rounded protuberances surmounted by setae.  Rows of spines occur ventrally upon the various segments.  In Fortisia foeda, each body segment except the last bears many small oval plates, each of which terminates in a strongly sclerotized tooth (Thompson, I915c). The extreme development of this type of larva in the family is found in Gymnocheta alcedo Lw. described by Thompson (1923d), in which each segment bears a single dorsal plate and a pair of pleural plates, and in species of Ormia, Ormiophasia, and Euphasiopteryx described by Townsend.  The segments of the planidia of the latter genera are telescopic, and the plates occur in three series, the dorsal one being very wide and the others situated dorsolaterally and ventrolaterally.  The venter is unsclerotized.  Ormiophasia still further approaches the planidium type in that it possesses caudal cerci, a character found in the larvae of many Dexiinae.


The planidia are derived from eggs hatching in the uterus of the female or from membranous eggs deposited on the food plants of the host or in their general vicinity.  They are variously colored, owing to the pigmentation of the plates, and may be gray­ish‑white, brown, bluish‑green, or black.  As growth takes place, the plates become considerably separated, revealing the white body color. There is also an appreciable stretching of the thin intersegmental membranes, resulting in a distinctly banded appearance.  This is noticeable even in the freshly deposited larvae of A analis.  The species that retain the eggshell as an anchor to the substratum, and enveloping the caudal end of the body, have forwardly directed spines on the last one or two segments.  Typical of this group are Archytas analis, Bonnetia comta (Fig. 208C,D), and Ernestia ampelus.


The first‑instar larvae of Ophirionopsis and Ophirion are markedly different from other representatives of this group.  They are described by Townsend (193fi) as being somewhat caterpillar‑like and very active; the former is stated to have eight pairs of "pseudolegs," which are half as long as the thickness of the body, and it has, in addition, three anal pseudopods.  In Ophirion, the pseudolegs occur on the 4th to the 10th and on the 12th and 13th segments.


The occurrence of light‑colored planidia is exceptional and a number described as such are believed to represent larvae deposited prematurely or dissected from the uterus and mistakenly believed to be mature.  All larvae of this type have open caudal spiracles. 


The three first‑instar larval forms described above are separated on the basis of adaptive characters, which are of independ­ent development in widely separated genera and higher groups.  The morphological char­acters of value in classification require too detailed treatment to be adequately sum­marized here, but in general they relate to various details of the head structure, the buccopharyngeal apparatus, the arrangement and form of the integumentary spines, the sensory organs, the caudal spiracles, etc.  Principal studies upon the classification of these larvae have been by Thompson (1922; 1923b,c; 1924), who concluded that they present adequate characters for specific determination, though the groups set up on this basis are not always in accord with those based upon the taxonomy of the adults.  He pointed out further that it is often difficult or impossible to distinguish between larvae of species which are quite distinct in the adult stage and, conversely, that it is at times possible to distinguish definitely between larvae of forms which, in the adult stage, are apparently identical morphologically (varieties of Lydella stabulans Meig.).


In practically all first‑instar larvae, the number of abdominal segments recorded has been eight.  There is a considerable range of variation in certain of the morphological characters that are not associated with a particular type of larva but that are used in the classification of the smaller groups. Some of these are discussed briefly herewith.


The buccopharyngeal apparatus consists, with very few exceptions, of a simple, unjointed structure, of which the three principal parts are the median tooth and the intermediate and basal regions, the latter of which may be only lightly sclerotized.  ­The relative lengths of these three parts vary greatly.  The outer, or dorsal, margin of the tooth may be smooth or bear a number of teeth.  The lower wings of the basal region are deflected somewhat ventrally, whereas the upper ones are usually consider­ably arched. There are frequently small lateral plates at the sides of the median tooth, and the small salivary-gland plate, often delicate and inconspicuous, lies beneath the intermediate region.  The anterior lateral plates at each side of the median tooth can frequently be recognized, though they may be very lightly sclerotized. A distinctive form of the buccopharyngeal structure is found in Bigonichaeta setipennis in which the intermediate region is in the form of a straight elongated rod, quadrangular in cross section eight times longer than wide.  The basal region is short and feebly developed.


The sensory organs of the head are usually not greatly developed and are most conspicuous in Bigonichaeta.  In addition to the usual maxillary sensoria, there is a pair of prominent clavate sensoria dorsally just in front of the antennae.  The antennae are themselves remarkably developed, being cylindrical and about six times as long as wide, tapering abruptly to a point, and terminating in a hair‑like distal portion about 4X as long as the basal part.  In addition to the sensory setae of the body segments, there are circular sensory organs on the venter of the various

segments.  In some species, such as Argentoepalpus signifer Wlk. and others described and figured by Thompson, there are rod‑ or club‑shaped sensoria an the thoracic and last abdominal segments. In many species, the antennae are small and somewhat conical in form, without a terminal hair.


The tracheal system of the first‑instar larva, which is present in the very great majority of species, consists of two main longitudinal trunks, with relatively few branches; they are connected by a posterior commissure.  The posterior spiracles usually consist of two papillae, each spiracle consequently being kidney‑shaped in outline, though a few species have simple circular spiracles with only a single opening.  In Dexia ventralis (Fig. 209E) and Theresia claripalpis, the spiracles are borne upon short cylindrical stalks; in Billaea pectinata Meig. (Tolg, 1910), the stalks equal one body segment in length, and they also bear three long setae at the distal end.  The atrium, spiracular, or "felt" chamber may be only as long as wide (Leschenaultia exul) or range to 15 to 20 times the width (Bigonichaeta setipennis).  It has been mentioned that spiracles are lacking in a number of species of microtype larvae, and they are likewise missing in Actia diffidens and Sturmia pelmatoprocta B. & B.  Anterior spiracles are quite uniformly absent in the first instar, though Landis states that they are present in Paradexodes epilachnae.


Second‑instar Larvae.‑‑The larvae of this instar show a much greater uniformity than do those of the preceding instar, as is expected in view of the occurrence of all species in the same environment, that is, within the body of the host.  The factors of locomotion, desiccation, penetration, and mechanical injury are all absent; and consequently adaptations to meet these conditions are lacking.  In all species, the integument is thin and transparent, the most conspicuous change in this respect being among the planidium‑type larvae, which discard the heavy integumentary armature of plates, scales, etc., at the first molt.


Generally, the cuticular armature of this instar consists of bands of setae, usually rather delicate, about the thoracic segments, on the venter of the abdominal segments, and in the form of a large patch on the last segment, often accompanied by a rather heavy band on the penultimate segment.  These setae are often arranged in irregular and broken rows.  In some species, the spines are much more numerous than in the preceding instar; in others, they are much less conspicuous.  Several species having heavily spined planidium‑type larvae are, in this instar, virtually devoid of spines.  In several species, rather conspicuous departures from the normal spine arrangement are known.  The larva of Gonia capitata has patches of minute black spines on the dorsum of the first thoracic segment and on the venter of the second, which are so dense as to give the appearance of black plates.  The spine patches on the venter of the last abdominal segment reach a maximum development in Anetia hyphantriae and are said to invaginate to serve as false feet, though the locomotory requirements of this instar are quite limited.  The spines of the last two segments of the great majority of species are usually directed cephalad, and they serve to hold the larva more firmly in position in the respiratory funnel.


The larva of Centeter cinerea is distinguished from others of this instar by the possession of a pair of conspicuous anal lobes which may be homologous with those of the same instar of certain Conopidae.


The buccopharyngeal apparatus is more robust and highly developed in the second than in the first instar, and there is, of course, much variation in the form, relative size, and sclerotization of the different parts.  In all species, the paired mandibular hooks are present, in contrast to the single median tooth of the first instar. A few species, such as Zenillia libatrix, Bigonichaeta setipennis, and G. capitata, have no articulations, the entire structure apparently being fused into a single piece.  The majority, however, have one articulation, which is usually between the anterior and intermediate regions, though in some it is between the intermediate and basal regions.  Archytas analis, Bonnetia comta, and Siphona geniculata have two articulations, separating the three principal parts of the structure.


The respiratory system of the second‑instar larva is also much more highly developed than in the first instar, because of the greater need for oxygen.  The two longitudinal trunks are heavier, with a considerable number of branches, and both posterior and anterior commissures are present.  In about half the species that have been studied, the anterior spiracles are said to be lacking, but in many instances they have probably been overlooked; for they are often very minute and situated intersegmentally in the pleural area between the first and second thoracic segments, and, in this position, any shrinkage or contraction of the body would tend to obscure them.  Each anterior spiracle usually has two or three papillae, the number being increased to 3-5 in Bigonichaeta setipennis, 5-6 in S. geniculata, and 6-9 in Lydella stabulans.  In Ernestia ampelus, however, they appear as simple circular openings, and those of Billaea pectinata are mere slits in the integument, and are recognizable only in prepared sections.


The posterior spiracles of the majority of species are widely spaced and have two papillae, lobes, or spiracular slits, though Actia diffidens has only one and Leschenaultia exul and Siphona geniculata have three.  An exceptional modification is present in the posterior spiracles of Centeter spp. (Fig. 210C) in the form of a large, ventrally directed, conical process immediately beneath the openings, which is believed to aid in perforating and maintaining connection with an air sac of the host.  This process in Hamaxia incongrua (Fig. 210D) is more sharply pointed and directed dorsad.  In Anetia and related forms, the stigmatic hooks, described for the first instar, persist in somewhat modified form. That they are functionless is improbable, in view of the development of a respiratory funnel during this stage.  The spiracular chamber in most species is very short, often being broader than long.  The only instance of complete lack of spiracles in the second‑instar larva is that of Fortisia foeda cited by Thompson, though the internal tracheal system is present and the trunks are filled with air.


Third‑instar Larvae.‑‑The mature larva is usually somewhat crescentic in lateral view, with the venter concave and the abdominal region broadest.  In some species, as Chaetogaedia analis v.d.W., the caudal segment is approximately the same width as those preceding it, whereas in others there is an appreciable tapering caudad.  The segmentation is distinct, though frequently obscured by segmental folds.  The larvae of Zenillia roseanae and Actia diffidens have distinct median pseudopodia ventrally between the abdominal segments.  The anal opening occurs at a variable distance beneath the posterior spiracles, often near the anterior ventral margin of the last segment.  The integumentary armature, consisting of spines and hairs, may be somewhat more extensive than on the preceding instar.  The larvae of Bonnetia comta, Bonichaeta setipennis, Racodineura antiqua, Dexia ventralis, and Prosena sibirita are almost bare, whereas that of Sturmia inconspicua is almost completely covered with setae.  More frequently, however, the thoracic segments and the last one or two abdominal segments bear complete bands of setae, whereas on the intervening segments they are largely ventral.  The setae of the anterior segments are directed caudad and on the posterior segments usually cephalad.  In Centeter cinerea, the central area of the last segment is covered with a patch of heavy black spines.  The so‑called spiracular hooks of Zenillia spp. persist in the form of clusters of three or four black spines, the bases of which are fused.  These are apparently homologous with similar groups found in the same position on certain conopid larvae.  The sensory organs are often reduced in size and number as compared with those of the preceding instars. The four pairs of finger‑like organs on the last segment persist in Zenillia libatrix.


The buccopharyngeal apparatus is more robust and highly developed than in the preceding instars.  The majority of species now have distinct articulations separating the three principal regions.  A considerable number of species, however, have only one articulation, which in some cases occurs between the anterior and intermediate regions and in others between the latter and the basal region.  Bigonichaeta is dis­tinctive in having the entire structure in one solid piece.  It is thus seen that the third‑instar larvae of the family normally have two articulations, but frequently only one and rarely none; the second‑instar larvae most frequently have one, but occasionally two or none; and the first‑instar larvae usually have none, but very infrequently one or two.  In no instance is a smaller number of articulations present than in the preceding instar of the same species.  B. setipennis and a species given by Nielsen as Ernestia connivens Zett., but later stated to be Plagia trepida instead, have no articulations in any instar; Zenillia spp. have none in the first and second and one in the third instar;  Lydella stabulans has none in the first and one in the following two instars; and Leschenaultia has none in the first two and two in the third instar.  Several species have none in the first and two in the last two instars.  The greater number of species have none in the first, one in the second, and two in the third instar.


The anterior region is quite generally in the form of paired mandibles which are distinctly hooked.  The hypopharyngeal and epipharyngeal sclerites are situated immediately beneath the juncture of the anterior and intermediate regions.  Each of these bears clear areas which are believed to represent sensory organs. Those of the epipharyngeal sclerite particularly are variable in number and form and are considered to be of value in making specific determinations.


The respiratory system reaches its greatest development in the third‑instar larva, as is to be expected from its greater size and the probable complete cessation of cutaneous respiration.  It consists of a pair of heavy longitudinal trunks, anterior and posterior commissures, and anterior (occasionally absent) and posterior spiracles.  In Bonnetia comta, each trunk is reported to have a diameter equal to one‑fourth that of the body.  According to Rennie & Sutherland (1920), Siphona geniculata lacks the anterior commissure.


The anterior spiracles are situated dorsolaterally at the posterior margin of the prothorax and may be in the form of a single circular opening as in Winthemia quadripustulata; a circular plate bearing radiating slits as in Centeter (Fig. 210E), Hamaxia, and Bonnetia; or, more commonly, a conical process bearing a number of papillae.  These papillae may range in number from two to three in Zenillia spp to 30-35 in Billaea pectinata.  Occasionally, as in Siphona and Racodineura, the spiracle is fan‑shaped, with the papillae in a rows at the outer margin.  In Archytas analis and G. capitata, the spiracular chamber itself is bifurcate, with an opening at the end of each short branch.  In the former, the openings are elongate and curved.  The spiracular chamber is usually two or three times longer than wide.  The anterior spiracles are not believed recognizable if present in Sturmia inconspicua (Webber 1932) and are lacking in Leschenaultia exul, though the stubs of the tracheal branches are present.


The posterior spiracles are usually large, somewhat circular in outline, with the inner margins more or less flattened, occasionally almost straight, and encircled by highly sclerotized, usually black, peritremes.  In some instances, these spiracles are semicircular or even triangular in outline.  The peritremes may be shallow, or they may exceed the width of the spiracle, forming conical or subcylindrical bases.  Occasionally, as in Siphona and Ernestia rudis, they are incomplete, being broken on the inner margin.  In the great majority of species, the spiracles are situated above the transverse axis and occasionally are distinctly dorsal.  Very seldom are they separated by a distance greater than the width of one spiracle, and frequently they are almost contiguous.  The spiracular slits are usually straight or slightly curved and radiate outward from the spiracular scar, which itself is situated at or below the median transverse line and somewhat toward the inner margin.  The number of these radiating slits is variable, most frequently being 3 or 4 but ranging up to 6 in Eubiomyia calosomae and about 10, variable and often branched, in Bigonichaeta. In Racodineura, there are 30 short slits arranged side by side in the peripheral part of the respiratory area. Several species, such as Gonia capitata, show the smaller number of slits following the periphery rather than radiating from the vicinity of the scar.  An occasional species has exceedingly long, serpentine slits, which at times are extensively branched.  The three elongated slits of G. capitata and Sturmia inconspicua occur at the crests of pronounced ridges.


An unusual modification in form of the posterior spiracle is found in H. incongrua in which the face of the spiracle (Fig. 210G) is rounded and highly sclerotized, forming, with the peritreme, a broadly rounded cone surmounted at one side by three hook‑like spines, which are directed laterad.  In Carcelia gnava, the respiratory area is in three parts, with the openings small, irregular in form, without apparent order, and number­ing about 30. The spiracle of Steiniella callida Meig. has 80-100 minute openings (Nielsen, 1909), and that of Oedematocera dampfi Ald. is rosette‑shaped with the pores arranged in rows radiating from the center (Greene, 1927).  The spiracles of Fortisia foeda are very large and bulbous and surmount short, broad stalks.  The openings are small, irregularly placed, and very numerous.  A remarkable form is figured by Lloyd for Ginglymyia acirostris, in which the large spiracular stalks, which are oval in cross section, arise from a common base, definitely dorsal in position, and each one terminates in an elongate‑oval spiracle with a single elongated, curved opening at the center (Fig. 205D).  At the outer margin of the spiracle are 30 leaf‑like processes, of unknown function.  These spiracles represent a wide departure from the normal tachinid form.  In a number of species, several minute openings have been noted on the surface of the spiracle, which are stated to be those of the perispiracular glands.  The spiracular chamber is relatively short in most species, seldom being longer than wide.


Puparia.‑‑There is an exceedingly wide range of variation in form and general characters among the puparia of the Tachinidae. Those of a considerable number of species have been described in connection with biological studies of particular species, but the most detailed account yet available is that by Greene (1922), in which the puparia of 100 species, of muscoid flies, a large portion of which are of this family, are described and figured.  The author concluded that the puparial characters are adequate for specific determination.


The general form of the puparium is subelliptical and slightly widest in the mid­abdominal area, with both ends smoothly rounded. In a few species, such as Hamaxia incongrua, Cryptomeigenia aurifacies Walt., and Viviania georgiae B. & B., the abdominal region is much larger than the anterior, though occasionally it is somewhat narrower.  The posterior end is at times markedly truncate, as in Sturmia cubaecola and Chaetogaedia analis v.d.W., while in others the caudal segments may he progressively narrower, giving a distinctly pointed appearance.  Usually, the longi­tudinal axis is straight, though in Eutrixa exile Coq. there is a marked upward curve of the anterior region.  The segmentation is usually indistinct and is indicated by faint lines or by a variation in the pubescence; yet in Exorista confinis Fall. the intersegmental constrictions are very distinct on the entire periphery, and in several species they are pronounced on the dorsum.  In Pyraustomyia penitalis Coq. and others, the last abdominal segment is much reduced, forming a tubercle surmounted by the spiracles.  The anal opening is represented by a distinct groove at a varying distance below the spiracles, frequently occurring almost at the anterior ventral margin of the last segment.


The color of the puparia of any given species is quite variable and usually deepens appreciably with age.  In general, it ranges from the darker shades of red and brown to black and may be dull or have a silken luster.  The puparia of a considerable number of species are yellowish‑red, and that of Alophora pulverea pale‑yellow.  The outersurface of the puparium bears the armature of the third‑instar larva and may consequently be hairy, bare and smooth, or roughened by striations or rugosities.


The anterior and posterior spiracles are, of course, those of the third‑instar larva; and although they are still recognizable as such, yet they show appreciable changes.  ­The posterior ones are generally situated slightly above the transverse axis of the body; but they are definitely dorsal in Latreillimyia bifasciarta (Fig. 211A), though they are below the axis in a considerable number of species and conspicuously so in Tachinophyta floridensis Tns.  They may be only slightly raised above the surface of the puparium or borne upon pronounced tubercles, as in Anachaetopsis tortricis Coq. The spiracular slits correspond in form to those of the mature larva.  The outstanding variation in spiracle form and position is found in Ginglymyia acrirostris, which bears them on large and heavy individual stalks markedly dorsad in position.  The puparium of Thrixion halidayanum is distinguished by the occurrence of the  spiracles upon a common stalk, which is large and cylindrical and projects from the rounded posterior end.


The external prothoracic cornicles are lacking in the majority of species, but in those which bear them they appear as conical or subcylindrical projections through the puparial wall dorsolaterally near the posterior margin of the fourth segment.  The papillae usually number 6-20, though in Leschenaultia exul they exceed 100, distributed irregularly over the distal half of the cornicle.  In Actia diffidens there is only a single terminal opening.  In Siphona geniculata, the perforations through the puparial wall may be detected, though the cornicles do not protrude.


The internal prothoracic spiracles of the pupa (Fig. 210H), situated at the base of the prothoracic cornicles and beneath the puparial wall, are present in all species.  They are circular in outline and nearly flat and usually bear the minute papillae in double rows radiating from the center.  These rows are irregular and sometimes branching and number 5-6 in Zenillia libatrix.  The total number of papillae in the great majority of species is 200.


There are two lines of cleavage which separate the two halves of the puparial cap from each other and from the remainder of the puparial wall, and both these halves are broken away at the time of emergence of the adult fly.  The horizontal line of cleavage, separating the two halves, extends across the front and posteriorly at each side to a point in the anterior portion of the fourth segment.  The vertical line of cleavage passes completely around the puparium and through these points and is in front of the prothoracic cornicles of the pupa, if they are present.


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Additional references may be found at:  MELVYL Library]