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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>.
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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.