Pseudacteon spp. (Diptera: Phoridae) Effect on Foraging Strategies of Solenopsis invicta (Hymenoptera: Formicidae) and Spatiotemporal Monitoring in Urban Habitats



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Red imported fire ants (RIFA), Solenopsis invicta Buren are adversely affected by phorid flies in the genus Pseudacteon by instigating defensive behaviors in their hosts, and in turn reducing the efficiency of RIFA foraging. Multiple Pseudacteon species have been released in Texas and research has been focused on the establishment and spread of these introduced biological control agents.

Laboratory and field experiments were conducted to 1) determine a bait size preference of RIFA exposed to phorid fly attack, 3) determine a bait preference between two candidate baits, 4) investigate worker size abundance in the presence of phorid flies, and 5) determine the presence and distribution of phorid flies in urban environments.

Laboratory experiments were used to determine foraging intensity and resource removal by RIFA foragers exposed to either P. tricuspis or P. curvatus. Arenas were constructed to allow access to a choice between two candidate baits and foraging RIFA were exposed to phorid flies for a 24 hr period. Results showed daytime foraging was reduced in the presence of P. tricuspis while nighttime foraging was increased when compared to RIFA not exposed to phorid fly attack. Additionally, RIFA exposed to P. curvatus had increased daytime and nighttime foraging when compared to RIFA not exposed to phorid fly attack. RIFA foragers were attracted to a commercial bait much more than to a laboratory candidate bait, but foragers removed more of the whole particles of the laboratory bait.

Field experiments were conducted to determine grit size selection of RIFA when exposed to phorid populations. Four different grit sizes of two candidate baits were offered to RIFA foragers. Foragers selectively were attracted to, and removed more of the 1-1.4 mm grit than any other bait size. The industry provided bait is primarily made of particles in the 1.4-2.0 mm size, larger than what was selected by the ants in this study. While there was a preference for foragers to be attracted to the industry provided blank bait, RIFA removed more of the nutrient rich candidate bait from the test vials. There was an abundance of workers in the 0.5-0.75 mm head width category collected from both field sites. This was dissimilar from a previous study where phorid flies were not active and in which large workers were collected in higher abundance at the site where phorids were not active. The implication is that phorid fly activity caused a shift for RIFA colonies to have fewer large foragers.

The population levels of RIFA and Pseudacteon species flies were investigated in urban areas of central Texas. The objectives of this study were to determine the presence of phorids, their distribution, and seasonal variability in urban environments. Phorids were found in all types of urban environments examined and during all seasons. There was no difference in the population levels of phorids based on urban environment type and summer and spring were the seasons in which phorids were most abundant.