The family Phoridae is a large group of small (0.5-6.0 mm long) flies that are found worldwide. The 4,000 species that are currently known may represent as little as 10% of the actual total number of species. In the phorid genus Apocephalus, 275 described species are found only in North, Central, and South America. These flies are parasitic, mostly on ants, and the larvae feed on ant tissue and often decapitate their ant host. In addition, the parasitic flies may have profound effects on a variety of ant behaviors. In this project, approximately 400 species of Apocephalus will be revised (the rest of the genus having been previously treated by the PI). Many new species will be described, their relationships investigated using both DNA sequences and body structure, and a new classification proposed. Field work in North America (Arizona, Texas) and the New World tropics (Argentina, Costa Rica, Peru) will uncover additional new species and host-parasite associations.
These flies have a strong potential to be used as biological control agents of their host ants. This project will make Apocephalus species available as possible biocontrol tools by providing published and online keys for identifying the species, and making web pages so that information about them is generally available. Two new graduate students will be trained in the project, providing more expertise on phorid fly identification and broadening the scope of the project.
This research continued to document the almost unbelieveable diversity and species richness of the genus Apocephalus. These are small flies (figure 1) that lay their eggs in the bodies of their hosts, usually species of ants, but also bees and some beetles. The feeding of their larvae eventually kills the host. Because many of the larvae feed in the heads of the hosts, and some heads fall off before the rest of the body stops moving, this genus is colloquially called the "ant decapitating flies". Depending on the species of host this parasitic lifestyle can be considered beneficial to humans (such as when pest species of ants are attacked), or as having negative consequences (such as when honey bees are attacked). Greater knowledge of this group will allow us to utilize these flies as biological control agents when ants become problematic, or to mitigate the negative consequences of those attacking more beneficial insects. As a result of Museum and field studies in this project, over 250 new species of Apocephalus were discovered, and are in the process of being described. Many new host associations were documented, including the association of Apocephalus borealis with honey bees. As a result of analysis of 6 gene regions in the DNA of Apocephalus specimens, we established a phylogeny of their relationships (figure 2). Plotting their hosts on the phylogenetic tree shows that the flies are generally associated with 3 groups of host ants: Camponotus (carpenter ants), leaf cutter ants such as Atta and Acromyrmex, and Pheidole. Interspersed among these hosts are species that attack other types of ants, mostly highly predatory ants such as army ants, ponerines, and bullet ants. Possibly, these predatory ants became hosts when mistaken attacks took place during raids on the more "normal" hosts. One group of Apocephalus, previously called subgenus Mesophora, attacks an array of non-ant hosts. Their hosts include bees, soldier beetles, wasps, and fireflies (a family of beetles called the Lampyridae). Because of their body shape and other morphological characters, as well as their highly divergent hosts, Mesophora were classified in a separate subgenus than the rest of the ant decapitating flies, which are classified as subgenus Apocephalus. The results of this project, however, clearly shows that these flies belong in the group attacking Pheidole ants, from which they evidently diverged in their newer hosts. Since they are nested well within the rest of Apocephalus, the subgenus Mesophora is no longer recognized, and we knew we place them within an informally Apocephalus wheeleri group. Additional studies that took place during this project produced new family classification for the Phoridae based on thoracic structure, found a new type of and decapitation in the family Phoridae (where adult females decapitate the ants) , the first ant parasitizing phorid from New Zealand (apparently introduced from Australia, as was its ant host), and the world’s smallest fly (which is a parasitic phorid from Thailand).
