Impact of Methoprene and Pyriproxyfen on Pseudacteon tricuspis (Diptera: Phoridae), a Parasitoid of the Red Imported Fire Ant, Solenopsis invicta (Hymenoptera: Formicidae)

Endoparasitoid phorid flies, Pseudacteon spp. (Diptera: Phoridae) are important biological control agents of imported fire ants Solenopsis invicta Buren, and S. richteri Forel (Hymenoptera: Formicidae). The impact on phorid flies by insecticides, particularly insect growth regulators, used in controlling imported fire ants has yet to be explored. Red imported fire ants parasitized by Pseudacteon tricuspis Borgmeier were exposed to methoprene and pyriproxyfen, the active ingredients used in some fire ant baits. These chemicals are insect growth regulators (IGRs), which affect the reproductive capabilities of the colony, but have no acute toxicity to fire ant workers. An experiment tested the effects of the 2 IGRs on the phorid fly larva at 2 time intervals (d 6 and 10 post-parasitism), when the larva was present in the thorax and head of the adult ant host, respectively. The mean proportion of emerged P. tricuspis from methoprene and pyriproxyfen treatments was significantly reduced relative to the control. Timing of exposure to the IGRs (ds post-parasitism) did not have a significant impact on the emergence of the phorid fly.