Sensilla on the tarsi and ovipositor of the parasitic phorid fly, Pseudacteon tricuspis: role in fire ant location and selection of an oviposition site?

Pseudacteon tricuspis Borgmeier (Diptera: Phoridae) is one of four species of parasitic phorid flies, which have been introduced for biological control of imported fire ants, Solenopsis spp. (Hymenoptera: Formicidae), in the southern United States. Pseudacteon species are commonly referred to as decapitating flies due to their unusual life history. Attraction of females to fire ant workers is mediated by fire ant semiochemicals. Females then inject a single egg into the thorax of a worker ant. The first instar larva develops in the thorax, whereas the second and third instars develop in the head. A previous study by our group has characterized antennal morphology of P. tricuspis, including identification of putative olfactory sensilla, which may play a role in host location. It is likely that chemosensilla on other body parts of P. tricuspis, such as the tarsi and ovipositor, also play a role in host location, in particular at close range and in the selection of an oviposition site (thorax) on fire ant workers. We describe here the abundance and putative roles of sensilla types located on the tarsi (both sexes) and ovipositor (females) of P. tricuspis by using the silver nitrate staining technique.