BIOLOGICALCONTROL Oviposition Behavior and Development of Pseudacteon Flies (Diptera: Phoridae), Parasitoids of Solenopsis Fire Ants (Hymenoptera: Formicidae) LLOYD w: MORRISON, CHRISTIANE G. DALL'AGLIO-HOLVORCEM,l AND LAWRENCE E. GILBERT Department of Zoologyand Brackenridge Field Laboratory, University of Texas,Austin, TX 78712 Environ.Entomol.26(3): 716-724 (1997) ABSTRACT We studied the oviposition behavior and larval development of Pseudacteon phorid flies, which are parasitoids of Solenopsis fire ants. Four South American Pseudacteon spp., P. litoralis Borgmeier, P. tricuspis Borgmeier, P. wasmanni (Schmitz) and P. curuatus Borgmeier (which attack S. invicta Buren), and 2 North American Pseudacteoll spp., P. browni Disney and P. crawfordi Coquillett (which attack S. geminata [F.]), were evaluated. In labo- ratory tests, larger Pseudacteon spp. attacked larger Solenopsis workers. The mean worker size preferred was significantlylarger than the colony mean worker size for all but the smallest phorid species, P. curuatus, which preferred workers significantlysmaller than the colony mean. Within Pseudacteon spp., larger females preferred larger workers, but this relationship was significant only for the 2 North American species. Natural parasitism rates of Solenopsis workers by the 2 North American Pseudacteon spp. in the fieldwere low (0-2.42% per colony), but >90% of the overall size range of worker ants showed evidence of parasitism. Between U.8 and 31.0% of apparent ovipositionattempts resulted in successfulparasitism. Mean larval development times ranged from 13.0 to 18.4 d at 30°C and were shorter for North American species. Larval stages required 24.8--36.5%longer to develop at 25°C than at 30°C. Mean pupal development times ranged from 15.6 to 18.7 d at 30°C. In general, larger Pseudacteon spp. had longer larval and pupal development times. Overall, North and South American Pseudacteon spp. were similar in terms of oviposition behavior and development. KEY WORDS Pseudacteon, Solenopsis, biocontrol, parasitism, parasitoid, oviposition behavior THE PHORIDAEIS one of the most biologically di- verse families on earth, yet relatively little is known about this group of minuscule flies (Disney 1994). Phorids in the genus Pseudacteon have been sug- gested as potential biological control agents for the red imported fire ant, Solenopsis invicta Buren, in the southeastern United States. Early evaluations of Pseudacteon phorids as biocontrol agents in the 1970s, however, were not very favorable. Although Pseudacteon phorids had been observed apparently ovipositing on worker ants in the Solenopsis sae- vissima complex, attempts to rear adults and dis- sect out developing larvae failed (Williams et al. 1973). The fact that parasitism could not be proven and the observation that Pseudacteon phorids at- tacked relatively small numbers of worker ants led to the conclusion that Pseudacteon spp. were of "dubious value" as biocontrol agents (Jouvenaz et al. 1981). Recent work has led to renewed optimism, how- ever, that Pseudacteon spp. may be effective in re- I Currentaddress:DepartamentodeZoologia/LIIP, Universi- dadeEstadualde Campinas, CaixaPostal6109, Campinas, Sao Paulo13083-970, Brazil. ducing S. invicta populations. Their life history has been described (Porter et al. 1995a), proving that they are, in fact, parasitoids of fire ants. Studies of responses of Solenopsis fire ants to Pseudacteon phorids indicate that colony-level foraging behav- ior is disrupted in the presence of phorids (Feener and Brown 1992, Orr et al. 1995, Porter et al. 1995b; L.W:M. and L.E.G., unpublished data). This indirect effect of phorids may have a much greater impact on Solenopsis populations than the direct effect of host mortality. Additionally, Pseu- dacteon spp. have been found to be very specific to individual Solenopsis spp. or species complexes (Disney 1994, Porter et al. 1995c; Gilbert and Morrison 1997). Despite these recent findings, much still re- mains to be discovered concerning the biology of Pseudacteon phorids and how they interact with Solenopsis ants. For example, the larval develop- ment of Solenopsis-attacking Pseudacteon spp. has been described for only 2 South American species (Porter et al. 1995a, 1997a), although 23 Pseudac- teon spp. are known to attack Solenopsis spp. (Dis- ney 1994). Several observations suggest that Pseu- 0046-225X197/0716-0724$02.00/0 © 1997 Entomological SocietyofAmerica