Description & Statistics
Megaselia fasciata Fall is a well known parasitic species of Phoridae. it is gregarious and internally parasitic of the pupae of many coccinellid genera in Europe (Lichtenstein 1920, Menozzi 1927). The number of individuals developing in each host is dependent on the size, but 8-14 reach maturity in each pupa of Coccinella. The parasitoid may sometimes act as an important natural control of the increase of these beneficial beetles, as shown by the fact that a parasitization of 48% has been noted on Adalia. During oviposition the female stands transversely on the thorax of the freshly formed pupa and curves the ovipositor beneath it, and the eggs are laid externally in small clusters between the legs. Sometimes eggs are also laid on the bodies of larvae that are approaching the time for pupation. Embryonic development is well advanced at the time of oviposition, and hatching may occur within 3 hrs. However, Lichtenstein (1920) noted that external incubation took 1.5 to 2.6 days. The eggshells fall from the host soon after hatching, and thus there is no external evidence of attack. The newly hatched larvae immediately penetrate the body at the base of one of the legs, and their ensuing development is very rapid. Feeding is completed in 2-5 days, after which the larvae emerge through an opening between the head and thorax to enter the soil to pupate. Parasitized pupae retain their normal form, although in death they assume an erect position which contrasts to the horizontal position of healthy pupae. Female flies feed on body fluids exuding from punctures made with the ovipositor, a habit that seems closely associated with oviposition (Clausen 1940/62).
Balduf (1928) found that oviposition of M. aletiae Comst. on Achatodes zeae Harr. usually occurs only when the larvae are sick or feeble, and the species is thus more a scavenger than a parasitoid. Such larvae enter the body through the anal opening rather than by penetrating the integument. The mass of larvae that develop causes the posterior 1/3rd of the host body to be much distended. They enter the body cavity, and the store of adipose tissue is the principal food source. The larval stage is completed in 11-15 days, and pupation occurs in the host tunnel. With M. giraudii Egger, a parasitoid of the grasshopper Phasgoneura viridissima L. in Europe, an adult host, fully active at the time of capture, later yielded 12 mature maggots of Megaselia. These emerged from a large opening in the integument at the side of the mesothorax. Dissection of the host remains revealed that the muscular tissue of the thorax had been completely consumed (Timon-David 1938).
Some species of Megaselia are parasitic on myriapods. Megaselia juli Brues was the first species noted to have this habit. Several instances of groups of females persistently attacking live individuals were observed by Myers (1934), this continuing in each case for several hours. Hosts make strong but unsuccessful efforts to ward off attacks. The phorids always approach with the ovipositors extended, centering their attention to the head region. Larval development is complete in ca. 3 days, and the body contents of the host are completely consumed by the maggots. Megaselia cuspidata Schmitz, in attacking a European myriopod, Iulus sabulosus L., oviposits in minute wounds in the integument (Picard 1930). However, the species is a true parasite because these wounds by themselves would not result in death. Berland (1933) believed that the larvae of Phoridae attacking ants and myriapods, are able to gain entry to the body cavity of the host only through wounds. Hypocera incrassata Meig., is a solitary internal parasitoid of the larva of the bibionid fly, Bibio marci L. in England (Morris 1922), solitariness being rare in the family. The mature larva emerges from the dead host and pupates in the soil.
Serious losses are inflicted in apiaries in Brazil through the attack of Melaloncha ronnai Borgm. on adult bees (Ronna 1936, 1937). Mortality of up to 50% has been observed, with the highest figures usually being found in apiaries located in shady and damp areas. The female lays her egg in the abdomen of the bee. The young larva causes an appreciable displacement of abdominal organs, but apparently produces no serious injury. It soon migrates into the thorax where it feeds on muscular tissue and quickly matures. Parasitized bees have difficulty flying and finally fall to the ground, walk about irregularly for a time and die. The thoracic tissues are almost entirely consumed, and the head and prothorax of the bee become detached from the rest of the body or remain connected with it only at one side. Pupation occurs most often within the thorax of the dead bee, with the anterior end of the puparium exposed. This species is generally solitary, although sometimes two individuals attain maturity in a single host. The egg and larval periods are completed in ca. 10 days, and the adult fly emerges 3-4 weeks later. Ronna (1937) recommended the use of glass traps containing a soap solution in which dead bees have been placed to control this phorid. The decomposing mass is attractive to Melaloncha adults.
Although many species of Phoridae are associated with ants in various ways, only the parasitic species are herein discussed. These are included in a large number of genera, of which Plastophora is most common. Borgmeier (1928, 1931) listed the species of 5 genera known to parasitize ants of the genus Atta and related forms. All are characterized by a pronounced development of the ovipositor, this being extreme in Myrmosicorius (Clausen 1940/62). Apocephalus pergandei Coq. is a solitary internal parasitoid of carpenter ant workers, Camponotus pennsylvanicus De G. (Pergande 1901). The female fly jumps on the ant in the open and lays the egg on its head. The young larva then enters through the occipital foramen. Feeding is confined to the contents of the head, which is completely hollowed out and detached from the body. Pupation also occurs within the head cavity. Fox (1883) probably observed this species also, for the host species and larval habits are identical. The adult fly was not secured in that study. Megaselia conica Malloch was reared from the abdomen of C. pennsylvanicus (Clausen 1940).
Wasmann (1918) made extended observations on Plastophora species. He described the association of P. formicarium Verr. with Lasius spp. It is also known to attack Myrmica and other genera in Europe. The adult flies hover, sometimes 50-60) over the ant nest, or at any points where the ants congregate, and are seemingly attracted by their odor. Only worker ants are attacked, the winged males and females being ignored. Also, dead or injured ants lose their attractiveness, and the species is thus not a scavenger. The female pounces on the worker from the air, the latter making a determined effort to escape or to defend herself. After alighting, the parasitoid persistently follows in the rear of the ant, always centering her attention on the abdomen. She finally pounces on her prey and presumably inserts the ovipositor dorsally between the abdominal segments (Clausen 1940/62).
Plastophora crawfordi Coq. and P. spatulata Malloch attack the fire ant, Solenopsis geminata F., workers in Mississippi. The female strikes the ant from above with great rapidity, seemingly in the anterior portion of the body. The prey falls on its side and is stunned or paralyzed for several seconds. It is thought that these species are parasitic, but they have not been reared from this host. Almost identical habits were found in Plastophora sp. attacking Camponotus in Europe by Fage (1933). The parasitic relationship between Plastophora and ants has been generally accepted by various researchers, and P. formicarium in particular has received attention. The activities of the female flies and the form of the ovipositor certainly lead one to believe that there attack is for purposes of oviposition directly into the body of worker ants. However, Clausen (1940) noted that no proof of this was available. The larvae were not taken from the bodies of ants, nor have the pupae been found under conditions that would definitely establish the relationship.
There are relatively few predaceous Phoridae, and those which are known to develop on the eggs of other insects and spiders. Termitoxenia spp. reportedly feed on termite eggs, while Megaselia epeirae Brues was reared from the egg sacs of spiders (Malloch 1912). An undetermined species was found in a very large port of the egg sacs in Japan, some containing up to 200-300 larvae and puparia.
Autuori (1928) and Fonseca & Autuori (1938) studied the biology and behavior of Syneura cocciphila Coq. (= infraposita B.S.). Autuori stated that this species was a gregarious internal parasitoid of the adult females of Icerya, but this was later found to be in error as its true status as an egg and larval predator was found. A maximum of 55 individuals can develop to maturity on the contents of one egg sac. Although feeding is mostly on the eggs, the maggots also attack young larvae during the time they remain within the sac. Larvae develop rapidly, and pupation occurs mostly inside the sac.
Phoridae are a large cosmopolitan family, with over 3,000 species. They are especially diverse in the tropics. Important morphological characters include a short antenna, 2 basal segments small, 3rd segment globular; wings (when present) with narrow triangle of heavy veins (S-c and R) in humeral area, extending along costal margin; branches of M and Cu parallel, weakly developed. The thorax is large, bristly and humpbacked. Many of the parasitic species possess a long, heavily chitinized ovipositor (Clausen 1940). The body is minute to small, and adults move with characteristic short, jerky movements.
Phoridae are primarily scavengers on decaying animal and vegetable matter or are scatophagous. Larvae and pupae of several species have been taken from mole nests. The myrmecophilous and termitophilous genera and species include the more degraded representatives of the family (Clausen 1940/62). Some develop as predators in egg masses of spiders and acridids. Entomophagous species exhibit a wide diversity in hosts. Most of the parasitic species are primary, solitary, endoparasitoids; a few species develop gregariously. Many of the parasitic species attack ant pupae and adult. Some species parasitize coccinellid pupae, larvae and pupae of Lepidoptera, larvae of Diptera, adult bees or myriapods. Those of predaceous habit develop on the eggs of spiders and locusts. Syneura cocciphila Coq. in South American and the West Indies, attacks eggs of the cottony-cushion scale, Icerya purchasi Mask. Several species have been found in egg cases of Locusta migratoria L.
Complete records of the food and host preferences for the family at the time were given by Malloch (1912). The division between the scavengerous and parasitic habits is not distinct; a species may develop in either way, or it may attack living organisms that, while still living, are in an unhealthy condition or are wounded and will soon die. Therefore, a species can seldom be considered as parasitic in the absence of experimental proof (Clausen 1940/62). Economically, the entomophagous Phoridae must be classed as predominantly injurious rather than beneficial, because of their general attack on coccinellid pupae, adult bees, and spider eggs. One truly beneficial species is S. cocciphila, a common enemy of the cottony-cushion scale. They have not been used successfully in biological pest control.
Brues, C. T. 1915. Wisconsin Nat. Hist. Soc. Bull. 12: 85-152.
Brues, C. T. 1950. Connecticut St. Geol. Nat. Hist. Sur. Bull. 75: 33-85.
Cole, F. R. 1969. The Flies of Western North America. Univ. Calif. Press, Berkeley & Los Angeles. 693 p.
Colyer, C. N. 1957. A new species of Plastophora (Dipt. Phoridae) from England: a short discussion of the evolution of the present concept of the genus and a key for the identification of the world species. Brotéria 26: 75-87.
Malloch, J. R. 1912. Proc. U. S. Natl. Mus. 43: 411-529.
Menozzi, C. 1927. Bol. Ital. Ent. Soc. 59: 72-8.