Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2018
Publication Date: 6/18/2018
Citation: Porter, S.D., Plowes, R.M. 2018. Biology and rearing of the decapitating fly Pseudacteon bifidus (Diptera: Phoridae) a parasitoid of tropical fire ants. Florida Entomologist. 101: 265-272.

Interpretive Summary: The small decapitating fly Pseudacteon bifidus is a parasite of the tropical fire ant, Solenopsis geminata. This fly is of interest as a self-sustaining biocontrol agent because tropical fire ants are invasive pests throughout the world's tropics, especially on Hawaii, Guam and other Pacific islands. In order to develop methods for mass rearing this decapitating fly, Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL and the University of Texas, Brackenridge Field Laboratory in Austin, TX conducted a series of rearing tests. The flies used in this study were collected near the Nueces River north of Catarina, Texas. The scientists found that P. bifidus parasitizes small fire ant workers. The sex ratio of adult flies was moderately skewed to males (58% to 42%). The average generation time was 30 days at 82 °F. Average larval development time was 14 days at this temperature, but about 15% of individuals took much longer (up to 4 weeks). Male pupae emerged about a day faster than female pupae. Unlike other decapitating flies, females were not ready to lay eggs until 8-24 hours after they emerged as adults. About 9,000 flies were able to be reared per generation with modified rearing procedures. The success of these rearing efforts was important because it provided a foundation for subsequent studies of P. bifidus host specificity and host suitability.

Technical Abstract: The small decapitating fly Pseudacteon bifidus Brown and Morrison is a parasitoid of the tropical fire ant, Solenopsis geminata (F.). This fly is of interest as a potential self-sustaining biocontrol agent because tropical fire ants are invasive pests throughout the world's tropics, especially on islands of the Pacific. The objective of this study was to develop methods for mass rearing P. bifidus and to study related aspects of its biology. The flies used in this study were collected near the Nueces River north of Catarina, Texas. We found that P. bifidus parasitizes minor workers with an average head width of 0.71 ± 0.10 mm (0.59 - 1.15, range). The sex ratio of adult flies was moderately skewed to males (58:42%) with males slightly more likely to emerge from the smallest hosts and females from the largest ones. The average generation time was 30 d at 27.6 °C. Average larval development time was 14.0 d at 27.6 °C, but the pattern was highly skewed with a mode of 11 d and about 15% of individuals in a long tail which extended out to at least 41 d. Male pupae emerged faster than female pupae (0.8 d, 23.5 °C). Unlike other Pseudacteon species, adult females were not ready to oviposit until 8-24 h after eclosure. We were able to rear 9500 ± 2800 flies per generation primarily by modifying preexisting rearing procedures 1) to provide adults access to water and sugar water so they could live longer, 2) by extending access to hosts for 1-2 extra days, and 3) by avoiding reuse of host colonies with poor rates of parasitism. Rearing efficiency was improved by rearing in discrete generations and the use of an attack box with automatic temperature, humidity, lighting, and mechanical controls that allowed flies to emerge, mate and parasitize hosts without the need of constant management. The success of these rearing efforts provided a foundation for subsequent studies of P. bifidus host specificity and host suitability.