Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2003
Publication Date: 6/1/2003
Citation: Vogt, J.T., Porter, S.D., Nordlund, D.A., Smith, R. A modified rearing system for production of Pseudacteon curvatus Borgmeier (Diptera: Phoridae) that parasitize imported fire ants. Biological Control. 2003. Interpretive Summary: About 20 flies in the genus Pseudacteon (phorid flies, decapitating flies) are known to parasitize imported fire ants. These flies are native to South America, where imported fire ants originated. The female fly lays a single egg in a fire ant worker, and the maggot makes its way to the head where it eventually (2-3 weeks) consumes the entire contents. This usually results in the ant's head falling off, thus the common name "decapitating flies." Because the presence of these ants causes fire ants to slow or stop their foraging activity, there is great interest in integrating them into biological control programs for self-sustaining, long term suppression of imported fire ant populations. This interest led to the need for development of efficient mass-rearing technology to insure a supply of flies for research, release and establishment in the United States. Large "attack boxes" were developed, in which adult phorid flies attack host ants. The ants, which usually cease activity and assume defensive postures when under fly attack, are induced to trail within trays in the box with an automated system of "lifter cups." Each tray has a pair of cups that alternate up and down; the ants hide under the cup in the "down" position until it is raised, then run across the tray to hide under the other cup. This keeps the ants exposed to fly attack. The original attack boxes are housed in rooms with high relative humidity to prevent desiccation of the adult flies. A modified attack box was developed, using steam-generated humidity and infrared heating elements for environmental control. Two phorid species are currently being reared in the United States using these systems. The large, automated attack boxes reduced labor associated with rearing the flies with previous systems by approx. 75%, and improved environmental controls allow for easier manipulation of environmental conditions within the box as well as maintaining an environment outside the box that is suitable for other tasks.
Technical Abstract: A self-contained, climate-controlled box for exposing fire ants to attack by Pseudacteon parasitoids was developed. The initial system, which is being used to rear Pseudacteon tricuspis Borgmeier, consists of large (approx. 244 cm L X 97 cm W X 50 cm H), well-ventilated boxes ("attack boxes") housed in a climate-controlled room (approx. 28 C, 80% RH). Adult flies emerge into the boxes, which contain live host ants (Solenopsis invicta Buren). Host ants are confined in a series of trays within the box, each containing a pair of inverted cups under which the ants can hide. The cups alternate up and down, inducing the ants to trail back and forth within each tray. A modified system used for P. curvatus Borgmeier consists of closed boxes, thorough which preconditioned air is pumped to maintain high relative humidity. Steam is used to generate humidity in a small, temperature-controlled room from which conditioned air is drawn, and infrared heating elements mounted above the attack box prevent condensation. This new system maintains high relative humidity (range 80-90%) crucial for activity and survival of P. curvatus. System performance was monitored in 4 ways: (1) environmental conditions within the system (RH, temperature, dewpoint, and light intensity), (2) production of P. curvatus, (3) successful development and emergence of P. curvatus, and (4) attack rates throughout the box. The modified system is capable of producing >1400 flies / day / attack box. This system will be useful for researchers with limited space in which rearing and research activities are conducted simultaneously.