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DIPTERA, Conopidae (Stephens
1829) --
<Images> & <Juveniles> Description
& Statistics
Conopidae occur in tropical and temperate regions where more than 500
species are known. Important
morphological characters include a broad head, usually wider than thorax;
eyes large (but not as large as Syrphidae); antennae projecting forward, 3rd
segment with well-developed style (occasionally aristate). The ptilinum is present at eclosion; the body
is usually bare or slightly hairy. The
abdomen is petiolate, producing a "wasp-like" appearance. They bear a superficial resemblance to
Syrphidae. Females of several species
have the caudal segments of the abdomen modified ventrally into a pincerlike
form, which may be an adaptation, similar to the Tachinidae, for grasping the
host during oviposition. Other
species, such as Stylogaster spp.,
have long slender ovipositors (Clausen 1940/62).
These insects are called thick-headed flies, is a family of flies
within the Brachycera suborder of Diptera. Flies of the family Conopidae are
distributed worldwide except for the poles and many of the Pacific islands.
About 800 species in 47 genera are described worldwide, approximately 70 of
which are found in North America. The majority of conopids are black and
yellow, or black and white, and often strikingly resemble wasps, bees, or
flies of the family Syrphidae, themselves notable bee mimics. Conopids are
most frequently found at flowers, feeding on nectar with their proboscis,
which is often long.
The larvae of all conopids are internal parasitoids, most of aculeate
(stinging) Hymenoptera. Adult females aggressively intercept and deposit eggs
on their hosts in-flight, and the female's abdomen is modified to form what
amounts to a "can opener" to pry open the segments of the host's
abdomen as the egg is inserted. The subfamily Stylogastrinae, including the
genus Stylogaster, is somewhat different, in that the egg itself is shaped
somewhat like a harpoon, with a rigid barbed tip, and the egg is forcibly
jabbed into the host. Some species of Stylogaster are obligate
associates of army ants, using the ants' raiding columns to flush out their
prey. More research is needed to determine the life histories of most
Conopids.
Conopids are primary, solitary, endoparasitoids of adult Hymenoptera,
e.g., vespids, bees and sphecids.
They are not important in biological control, and may even be
considered pests because of their attack on pollinating bees. Aldrich (1930) reviewed the observations
that had been made on the genus Stylogaster,
which is associated with ants in the tropics. Some researchers believe that the flies oviposit in the ants
themselves or in other insects driven from their shelters by ants, and that
they are predaceous on the larvae, etc.
Clausen (1940) commented that parasitic development in the adult ants
is improbable because the fly is much larger than the ants. Silvestri (1926) found a larva, believed to
be a conopid, in the head of a Termes
gilvus Hag. worker in the
Philippines. Certain species may be
parasitic in Acrididae.
Because of a comparative scarcity, Conopidae are of little economic
importance except when they attack bumblebees. Severin (1937) noted that heavy losses can occur from Zodion fulvifrons Say as a parasitoid of worker honeybees in South
Dakota. Biology & Behavior
Saunders (1858) produced an early summary of the biology and behavior
of Conopidae). He described and figured
the mature larva and puparium of Physocephala
flavipes L, and called attention to
the conclusions of Robineau-Desvoidy & Dufour early in the 19th century
that these flies oviposit directly into adult Hymenoptera (Clausen
1940). Later researchers believed
that the eggs were deposited externally upon them, no eggs were ever observed
on the body or the eggshells of hosts from which larvae were taken. It had been maintained that the species
attacking Vespa oviposit in the
larvae in the nest and that maturity was reached when the host became an
adult. Pantel (1910) studying the
reproductive system of the females believed that oviposition was internal,
and studies by De Meijere (1904, 1912) on a number of European species of
Conopidae confirmed this conclusion that it occurs in the adult host. Eggs show now embryonic development at the
time they are laid.
During oviposition, the female pounces on the host and lays while the
latter is in flight. However, the
contact is only momentary. If the egg
is laid at this time, the insertion of the ovipositor must be exceedingly
rapid. There is no struggle between
parasitoid and host such as occurs during oviposition by Pyrgotidae. This manner of attack was noted in P. rufipes
F. and P. tibialis Say, which are parasitic on bumblebees in Europe. Female Conops
scutellatus Meig. congregate in numbers about the entrances of Vespa nests, pouncing on the wasps as
they enter. In a number of cases of
species known to parasitize nest-building wasps and bees, the females have
been observed to enter the nests, though it is not known that oviposition
took place therein. Because some
colonies show a high parasitization supports egg laying in the nest. Workers of social wasps are most often
attacked, although males and females are also at times.
The 1st and 2nd instar larvae seem to lie free in the abdominal
cavity, absorbing their food from the blood of the host. More extensive feeding occurs in the 3rd
stage, and all the contents of the abdomen are eaten. Several investigators have noted bees
feeding at blossoms which, on examination, were found to contain 3rd instar
conopid larvae. These larvae do not
enter the thorax, and the absence of injury to the muscles in that region
contributes to the continued activity of the host until the parasitoid larva
is almost mature. The 2nd and 3rd
instar larvae have their posterior spiracles firmly attached to one of the
tracheal air sacs. The host dies only
a short time before it completes larval feeding, and the dead bees or wasps
are usually found in the nest or near its entrance. A swollen abdomen may usually identify these.
Pupation occurs within the dead host's abdomen, the puparium
completely filling it. The position
in which it is found is constant, the body being inverted with respect to the
host and the head end at the base of the abdomen. One exception is Sicus
ferrugineus L., in which the head
is directed toward the caudal end of the host's abdomen, the change in
position having been made by the larva just prior to pupation. Adult flies emerge through a rupture of
the intersegmental membranes on the ventral side of the host, usually between
the 1st and 2nd abdominal segments.
If the disintegration of the host body has progressed too much, the
body may be broken in two at that point.
At emergence the anterior portion of the puparium breaks away in two
parts, one ventral and the other dorsal, and the posterior line of cleavage
of the latter is between the metathoracic and 1st abdominal segments. The majority of species seem to
have a single generation per year, with some possibly requiring two
years. Feeding is probably of short
duration (ca. 2 weeks) and winter is passed within the puparium in the dead
hosts (Clausen 1940/62). For detailed descriptions of immature
stages, please see (Clausen 1940/62) and <Juveniles>. = = = = = = = = = =
= = = = = References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Aldrich, J. M. 1930. proc. U. S. Natl.
Mus. 78: 1-27. Kröber, O.
1939. Beitrage zur Kenntnis der Conopiden. - Annals
and Magazine of the Natural History, Series 11,4: 38 1; London. Camras S. (1962): The Conopidae of
Madagascar (Diptera). - Mémoires de L'institute Scientifique de Madagascar.
Serie
E, 8: 18 1 ; Tananarive. Camras,
S. & P. Hurd. 1957. Calif. Insect Surv. Bull. 6: 19-49. Janssens, E. 1955. Remarques sur le
peuplement de l'ile de Chypre en Diptères Conopinae et description d'une
espèce nouvelle. Bull. Inst. R. Sci. Nat. Belgique 31. No. 87. p. 4. Parsons,
C. T. 1948.
Ann. Ent. Soc. Amer. 41: 223-46. Severin,
H. C. 1937. Ent. News 48: 243-4. Smith,
K. G. V. 1966. The larva of Thecophora
occidensis, with comments upon the biology of Conopidae (Diptera). J.
Zool., Lond. 149, 263-276.Keys larvae and pupae to genus (worldwide).Very
full world bibliography of biology and immature stages. |