File: <dipte1.ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
Enemy Groups > <Citations> |
Immature Stages
of Diptera
Clausen (1940) remarked that a noticeable degree of
specialization has taken place among the immature stages of parasitic groups
of Diptera as compared with the general predators, and no attempt will be
made here to group the latter with respect to egg, larval, and pupal
types. For an extended comparative
study of the mature larvae and pupae of a considerable number of families,
both orthorrhaphous and cyclorrhaphous, an early but excellent reference is
De Meijere (1917). Clausen (1940) discusses the different stages of Diptera as
follows: The Egg.--The egg types are: 1. The muscoidiform is
the most common; it is distinguished by having a thin and delicate chorion,
largely lacking in ornamentation, and ranges in form from elliptical to
elongate cylindrical. In the
Tachinidae and Sarcophagidae, these eggs usually undergo complete or partial
uterine incubation. Relatively few
are deposited internally in the host.
Other parasitic and specialized predaceous groups having membranous
eggs are the Agromyzidae (Cryptochaetum),
Phoridae, Pyrgotidae, Bombyliidae, Cecidomyiidae, and Nemestrinidae. 2. The encrusted egg is
similar in form to the above but has a relatively heavy waxy incrustation,
which may bear various striate or reticulate markings over the surface of the
chorion, giving it a pearly‑white color. This type is found generally in the Syrphidae, Drosophilidae,
and Ochthiphilidae. 3. The pedicellate egg is
ellipsoidal to elongate cylindrical in form, with a thin and transparent
chorion, and bears a stalk at one end by means of which it is attached to the
integument of the host or to an internal organ. In the Tachinidae (genus Carcelia
only), the stalk is at the anterior end and the tip is expanded to form an
adhesive structure, while in the Conopidae it is similarly situated and bears
the micropyle at its tip. The egg of
the parasitic cecidomyiid, Endopsylla
endogena Kieff., has a
minute stalk that is embedded in the wing of the psyllid host. Partial or complete uterine incubation
takes place in eggs of Carcelia. 4. The macrotype egg is
found only in the Tachinidae; it is broadly oval to ellipsoidal in outline,
with a thick, tough chorion on the dorsum and sides, and the ventral surface
is fiat and membranous. This type of
egg is attached externally to the integument of the host by its flat ventral
surface. Strong adhesion is ensured
by a mucilaginous material, which accompanies the egg at deposition. Very few of these eggs show any evidence
of uterine incubation. 5. The microtype egg is,
as its name implies of minute size; it may be ovate or almost circular in
outline, with the ventral surface thin and membranous, for attachment to a
leaf or other surface, and the dorsum and sides heavy, tough, and usually
highly sclerotized, with various surface markings. Many genera and species of Tachinidae deposit this type of
egg. The eggs of the Cyrtidae, which
are of somewhat different form and adhere to the substratum by the posterior
end rather than the ventral side, show no embryonic development at the time
of deposition, have a long period of incubation, and hatch without the
intervention of the host. In the
great majority of tachinid species, uterine incubation is complete, but
hatching takes place only after ingestion of the eggs by the host. This type corresponds to the microtype egg
of the Trigonalidae in the Hymenoptera. First‑instar Larvae.--The first‑instar larvae of the
parasitic and restricted predaceous groups show a degree of specialization
comparable with that of the egg forms.
Only the forms that depart from the normal for the higher groups to
which they belong will be considered here.
The greatest variety in larval forms is found among the Tachinidae,
which contains four of the five types listed below. 1. The muscoidiform larva
is the generalized type of the superfamily and includes the less specialized
Tachinidae and Sarcophagidae, the Pyrgotidae, etc. It is a plain maggot, without adaptive characters. 2. The microtype larva is
that which originates from the microtype egg of many Tachinidae. It is distinguished by its small size,
lack of extensive cuticular armature and the reduction and simplification of
the mouthparts. It hatches from the
microtype egg in the digestive tract of the host. 3. The planidium larva is
found generally among the Cyrtidae, Bombyliidae and Nemestrinidae and
frequently in the Tachinidae and in a few species of Sarcophagidae. A rather elongated form and a heavy
integument, often highly sclerotized, frequently bearing heavy spines, scales
or plates, and long caudal setae, except among the majority of tachinid
species, distinguish it. These
adaptations provide for an active and relatively long free life before the
host is reached. All larvae of this
type are followed by a generalized second instar which lacks the above
adaptations and is capable of very little ordered movement. [For a discussion of the planidium larva
in the different orders, see Clausen (1940), pages 17‑19]. 4. The vesiculate type of
larva is much less common in the parasitic Diptera than in the
Hymenoptera. Among the Tachinidae, it
is found in Plagia trepida Meig., and the vesicle
is in the form of a large plate occupying the main portion of the ventral
face of the last segment. It occurs
also in the Pipunculidae and possibly in the Conopidae, though in the latter
family the first instar has been little studied but the vesicle has thus far
been noted in the following instars. 5. The caudate larva is readily
recognized by its paired caudal appendages, which persist in the following
instars. Among the entomophagous
Diptera, it is found in the agromyzid genus Cryptolaemus that is parasitic internally in monophlebine
Coccidae. This larval form is found in
some aquatic or semiaquatic species that are not entomophagous in habit, such
as the calliphorid, Wilhelmina
nepenthicola Vill., of
Borneo. Mature Larvae.--Although there is a marked convergence in form in
the mature larvae as compared with the specialized first instar, yet many
groups have characters that can be readily recognized. We are particularly concerned with the
families or lower groups having parasitic larvae and with the highly
specialized predators. The general
characters by means of which they may be recognized, or at least narrowed to
certain limits, are as follows: Cecidomyiidae.--The head feebly developed and lacking mandibles;
body color often red, orange, or yellow; 13 body segments with lateral
abdominal spiracles present; of small size. Cyrtidae.--Body much the widest in the abdominal region, tapering
markedly cephalad; a constriction between thorax and abdomen and segmentation
evident only anteriorly; anterior and posterior spiracles present, the latter
simple in form. Bombyliidae.--Body crescentic, tapering at both ends, abdomen
9-segmented, with integument glistening and bare; anterior and posterior
spiracles present, the latter on the penultimate segment and comprising 8-12
openings arranged in a crescent or semicircle around a distinct button; the
anterior pair similar but smaller, or fan-shaped. Phoridae.--Segmentation distinct, though obscured by
supplementary folds, the parasitic species usually lacking the fleshy
integument processes; the buccopharyngeal armature in 3 parts with the
mandibular sclerite unpaired; anterior and posterior spiracles present, slightly elevated, the latter
usually with 4 openings. Pipunculidae.--Segmentation indistinct and mouthparts reduced;
anterior and posterior spiracles present, somewhat elevated, the latter pair
situated at the lateral margins of a single heavily pigmented peristigmatic
plate, and each usually having 3 openings; some species with the posterior
spiracles situated in a pronounced depression. Conopidae.--Body markedly pear‑shaped, with the thoracic
segments much attenuated, and the integument clothed with minute setae or
tubercles; anterior spiracles often lacking, but when present fan‑shaped,
with many openings; posterior spiracles very large, convex to hemispherical
and heavily sclerotized; the minute circular openings arranged in rows or groups, totaling 400 to
700, about a large button; a sclerotized process surmounted by several blunt
spines occurs slightly dorsad of each posterior spiracle; paired anal
vesicles present in some species. Pyrgotidae.--Body pear‑shaped, with the integument bare and
glistening; anterior spiracles stalked and fan‑shaped, whereas the
posterior ones are very large, of 3 main lobes with many small openings,
heavily sclerotized, and usually situated at the dorsal rim of a large median
depression. Agromyzidae (genus Cryptochaetum).--Body
segments distinct, each with a band of minute setae; the caudal segment with
paired tubular tails which may be several times the length of the body; the
anterior spiracles dart‑shaped or palmate and set in pits; the
posterior spiracles in the form of heavily sclerotized, posteriorly directed
hooks, with an opening at the base. Ochthiphilidae.--Abdomen 9‑segmented, segmentation
indistinct, with integument either bare or having numerous fleshy spines;
anterior and posterior spiracles present, the latter consisting of three
finger‑like structures terminating in simple openings that are borne
upon long, cylindrical, diverging processes or stalks. Sarcophagidae.--Body tapering markedly cephalad, with the
posterior end often bluntly rounded; integument clothed with minute spines;
anterior spiracles fan‑shaped, with 5 to 15 or more openings; posterior
spiracles with peritreme incomplete and the slits almost parallel, lacking
the button, and situated in the upper portion of a pronounced depression,
the rim of which bears fleshy processes of various forms. Tachinidae.--All general characters variable; integument usually
with bands of setae on each segment, which may be complete or broken;
anterior spiracles simple, plate‑like with several openings, or conical
with many minute openings on the distal portion; posterior spiracles usually
circular with peritreme complete, the slits most commonly numbering 3 or 4
and radiating from the spiracular button; the number of slits may range up to
30 and are most frequently straight but may be serpentine, branched or
broken, or occasionally in the form of numerous small openings, irregularly
placed or in rows. The Pupa or Puparium.--There are two distinct methods of pupation
in the Diptera, a fact that serves as the basis for division into two
suborders. In the Orthorrhapha, the
pupa emerges from the larval skin through a T‑ or + -shaped fracture,
whereas in the Cyclorrhapha the larval skin becomes heavily sclerotized and
hardens, forming n puparium enclosing the pupa. The lines of fracture of the puparium occur transversely on the
dorsum and venter of the first abdominal segment; and a horizontal fracture,
dividing the operculum into an upper and a lower half, extends across the
front. The adults of all families of
the suborder, except the Phoridae, Platypezidae, Pipunculidae, and Syrphidae,
are provided with a ptilinum, by means of which the operculum is forced off. Greene (1925b) presented a tentative
arrangement of the muscoid flies based upon the characters of the puparia. The characters of the pupae or puparia by means of which the
principal families may be recognized are as follows: Cyrtidae.--The body robust, the head markedly ventral, with the
thorax greatly arched and longer than the abdomen; prongs, hooks, and spines
lacking. Mydaidae, Asilidae, Nemestrinidae, and Bombyliidae.--The free
pupa somewhat elongated in form with the head bearing several pairs of large
heavily sclerotized prongs; a row of hooks on each abdominal segment, and the
last segment terminating in a pair of prongs. These pupae are capable of considerable movement. Therevidae.--As in the preceding families except that only two
pairs of prongs occur on the head and one prong at the base of each wing pad. Phoridae.--The dorsum of the puparium much less arched than the
venter, with the lateral margins compressed dorsoventrally, giving it
distinct boat‑like appearance; the surface dull owing to minute setae
or to the persistent fleshy spines of the larva; prothoracic cornicles of the
pupa extruded and small to large in size; the operculum, which includes the
cornicles, may consist of a dorsal and a ventral half or of only the single dorsal
plate. Pipunculidae.--Puparium broadly oblong in outline, occasionally
with the caudal spiracular area depressed; the pupal cornicles extruded and
minute to very large and conical in form; the operculum in two parts, the
dorsal part bearing the cornicles, or they may be situated on the line of
fracture. Conopidae.--Somewhat flattened dorsoventrally, the venter
frequently more convex than the dorsum, with the segmentation indistinct and
the surface smooth or wrinkled; pupal prothoracic cornicles not extruded;
posterior spiracles large and elevated. Pyrgotidae.--The venter of the anterior region much more convex
than the dorsum; posterior spiracles very large and, in most species,
situated on the dorsal rim of a pronounced posterior depression; surface bare
and shining; pupal prothoracic cornicles not extruded. Agromyzidae (genus Cryptochaetum).--Pointed
at the anterior end, with the segmentation distinct and the paired caudal
processes of the larva persistent; the anterior dart-like spiracles fully
extended and terminal in position, and the caudal spiracles hooked as in the
mature larva; pupal prothoracic cornicles not extruded. Ochthiphilidae.--Oblong in form, flattened ventrally, with
segmentation indistinct except in anterior region and the surface dull owing
to setae or persistent fleshy spines of larva; stalked posterior spiracles as
in the larva; pupal prothoracic cornicles not extruded. Sarcophagidae.--Oblong to somewhat cylindrical in form, the
segmentation indistinct and distinguished from the following family by the
large posterior depression within which the spiracles are situated and the
margin o# which bears fleshy processes or tubercles; spiracular characters as
in the mature larva; pupal prothoracic cornicles not extruded. Tachinidae.--Puparial characters
variable, as in the mature larva, usually barrel-shaped; pupal prothoracic
cornicles small and extruded in some species. References: Please refer
to <biology.ref.htm>,
[Additional references may be found at: MELVYL
Library ] |