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New species of fly parasitizes fungus-growing ant
STRI Panama

Larvae of the newly identified fly species Pseudogaurax paratolmos Wheeler grow up on a gory diet—the larvae of the fungus-growing ant Apterostigma dentigerum. The species is formally described by Cely González and co-authors working with Hermógenez Fernández-Marín, Smithsonian research associate and scientist at the Institute for Scientific Investigations and High-End Technology Services (INDICASAT-AIP). PhD student González discovered the new species in a larger survey of Apterostigma ant parasites.

“She noticed that some larvae looked different from the ant larvae, so she allowed them to develop—and out emerged flies of the genus Pseudogaurax,” said Fernández-Marín.

The researchers note that this species is the first known of its family, Chloropidae, to parasitize ants—while other chloropid flies include larvae that are parasites of bees, predators of spider eggs, and grass-seed eaters, P. paratolmos takes advantage of a new food source in the fungus ants.

The ant host is found through Central America and Brazil, living in nests that double as fungus gardens tended by small colonies of 30 to 100 individuals. The researchers collected 203 A. dentigerum ant nests, and observed fly larvae growing within 14 of the nests. A P. paratolomos fly lay a single egg upon an ant larva, which is swathed in fungal hairs that also serve as the ants’ food. Each hatched fly larva gradually consumes the ant larva it was laid upon, and pupates instead of the ant. While some of the emerging adult flies are attacked by adult ants as nest intruders, the fly larvae themselves are groomed and cared for just as the ant larvae are.

Emerging adults from the study were caught and preserved to describe a species new to science—type specimens are kept at the University of Panama and McGill. Further research may help answer questions about the new host-parasite relationship, including how the flies manage to evade attack when they enter the ant nests to lay their eggs.

Study co-author William Wcislo, STRI staff scientist and deputy director, says, “This discovery shows how little we know still about very basic aspects of natural history, as we can find new species and new modes of parasitism in a relatively well-studied group of ants,”

González, C. T., Wcislo, W. T., Cambra, R., Wheeler, T. A., and Fernández-Marín, H. 2016. A new ectoparasitoid species of Pseudogaurax Malloch, 1915 (Diptera: Chloropidae), attacking the fungus-growing ant, Apterostigma dentigerum Wheeler, 1925 (Hymenoptera: Formicidae). Annals of the Entomological Society of America. DOI: 10.1093/saw023

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