Funded by National Science Foundation
grant DEB-9407190 to Brian Brown

The genus Apocephalus Coquillett is a huge, poorly-known group of New World flies that parasitize a range of hosts. Found from rain forests near the equator to tree line in northern North America and southern Argentina (but absent from Chile), these small, 1-3 mm long flies belong to one of the largest genera of the family Phoridae. Before our work, there were 87 described species; the number is now 277 species and still climbing, with entire large groups and over 100 species still not revised.

Apocephalus is currently organized into two subgenera: Apocephalus sensu stricto and Mesophora Borgmeier. The species of Apocephalus s. s. are the true "ant-decapitating flies" that Brown (1997a) organized into 5 groups: the A. attophilus group (mostly parasitoids of attine leaf-cutting ants), A. miricauda group (mostly parasitoids of ponerine ants), A. pergandei group (mostly parasitoids of Camponotus carpenter ants), A. feeneri group, and A. grandipalpus group. Of these, Brown (1997a, 2000, 2002) revised the first three, leaving two large groups, the A. feeneri and A. grandipalpus groups, both mostly parasitoids of Pheidole ants, still awaiting treatment. There are a few species of Apocephalus that do not fall into any of these informal groups.

Species of the other subgenus, Mesophora, are highly divergent, both structurally and behaviorally. Unlike Apocephalus s.s., females of Mesophora species attack a diversity of non-ant hosts including stingless bees, spiders, wasps, bumble bees, and most commonly, cantharoid beetles (mostly fireflies- Lampyridae). Brown (1996) analyzed the relationships of Mesophora using morphology, and using the resulting phylogeny found that shift from ants to cantharoids was predated by an earlier switch in primitive Mesophora to stingless bees. Species in the firefly-parasitizing clade are common in middle elevation tropical sites, but the hosts of most species have not yet been found. One North American species was found to profoundly affect the population of fireflies in the eastern USA, an effect that probably extends throughout their range (Lewis & Monchamp 1994). Similarly, Brown (1997b) found that one of the stingless bee-parasitizing species caused tremendous premature mortality in males of a species of bee at La Selva, Costa Rica, and Otterstater et al. (2002) found the same with bumble bees in Canada. These small flies obviously have an enormous impact on their hosts that remains largely unstudied and unappreciated.

Apocephalus attacks a carpenter ant
photo by S. A. Marshall

Apocephalus paraponerae on
injured Paraponera clavata

All female Apocephalus attack their hosts by piercing them with the tip of their sharp ovipositor. In most species of Apocephalus s.s., the larvae develop exclusively in the ant's head, and often cause it to fall off, sometimes before the rest of the ant stops moving around- thus the common name "ant-decapitating fly." Most attack healthy, living ants, but species of the A. miricauda group are specialists on injured ants, and are thus easily collected by crushing their hosts. Many Apocephalus are associated with army ants, both as parasitoids of the army ants or attacking other ants flushed out by their raids.

Virtually nothing is known of the egg-laying habits of Mesophora species, and some (especially those attacking fireflies) are possibly nocturnal or crepuscular in their activity.

army ants

Brown, B. V. 1996. Preliminary analysis of a host shift: revision of the Neotropical species of Apocephalus, subgenus Mesophora (Diptera: Phoridae). Contributions in Science. 462: 1-36. PDF

Brown, B. V. 1997a. Revision of the Apocephalus attophilus- group of ant-decapitating flies (Diptera: Phoridae). Contributions in Science. 468: 1-60. PDF

Brown, B.V. 1997b. Parasitic phorid flies: a previously unrecognized cost to aggregation behavior of male stingless bees. Biotropica. 29: 370-372.

Brown, B. V. 2000. Revision of the "Apocephalus miricauda-group" of ant-parasitizing flies (Diptera: Phoridae). Contributions in Science. 482: 1-62. PDF

Brown, B. V. 2002. Revision of the Apocephalus pergandei-group of ant-decapitating flies. Contributions in Science. 496: 1-58. PDF

Lewis, S. M. & J. D. Monchamp. 1994. Sexual and temporal differences in phorid parasitism of Photinus marginellus fireflies (Coleoptera: Lampyridae). Annals of the Entomological Society of America. 87: 572-575.

Otterstatter, M.C., T.L. Whidden, & R.E. Owen. 2002. Contrasting frequencies of parasitism and host mortality among phorid and conopid parasitoids of bumble-bees. Ecological Entomology. 27: 229-237.

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