Pseudacteon Tricuspis Research Articles

Seasonal patterns of activity among species of black fire ant parasitoid flies (Pseudacteon: Phoridae) in Argentina explained by analysis of climatic variables

Abstract We monitored weekly relative abundances of adult female Pseudacteon (Diptera: Phoridae) species between February 1998 and May 2000 in Argentina. Fire ant-phorids were active around mounds of Solenopsis richteri Forel throughout the year. Phorid species richness ranged from six species during the summer-fall, to a single, large species during the winter. Species were classified as winter, summer, or fall-spring species, depending on times of peak mean abundance. We used descriptive multivariate techniques to analyze phorid phenological data (correspondence analysis), climatic data (principal component analysis), and their relationships (canonical correspondence analysis=CCA) at three temporal scales. The long-term mean temperatures, the mean and minimum sampling-time temperature, and the cumulative number of days without rain from the two months preceding each sampling day explained >90% of the variance when the data for sampling dates were averaged across the same months over the two years. Pseudacteon borgmeieri Schmitz, the winter dominant, was associated with lower temperatures and rainfall, whereas Pseudacteon curvatus Borgmeier, the summer dominant, showed the opposite pattern. Among the fall-spring species, Pseudacteon comatus Borgmeier was associated with months of higher maximum temperatures, longer photoperiods, and lower relative humidity. Pseudacteon nudicornis Borgmeier, in contrast, showed the opposite pattern. Pseudacteon tricuspis Borgmeier, was associated with months, typically in fall, having greater rainfall and fewer days with frosts. Implications of these patterns for the process of selecting particular species of S. richteri-attacking Pseudacteon for use in biological control introductions against imported fire ants are discussed in relation to climates of source and release areas.

A modified rearing system for production of Pseudacteon curvatus (Diptera: Phoridae), a parasitoid of imported fire ants

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 (about 244 cm L × 97 cm W × 50 cm H), well-ventilated boxes (“attack boxes”) housed in a climate-controlled room (approx. 28 °C, 80% RH, 12:12 (L:D) h). 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 Pseudacteon curvatus Borgmeier consists of closed boxes, through 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, dew point, 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.

Developmental rates and host specificity for Pseudacteon parasitoids (Diptera: Phoridae) of fire ants (Hymenoptera: Formicidae) in Argentina.

This study extends our comparative knowledge of Pseudacteon interactions with Solenopsis fire ant workers. Reported in this work are development times for seven Argentinean parasitoid species reared on two hosts, Solenopsis richteri Forel and Solenopsis invicta Buren, under laboratory temperature regimes comparable with those of the climatic zones occupied by these host species. Developmental times spanned 31-66 d across phorid species, and in general did not differ between genders or host species, but were longer at lower temperatures. The size distribution of flies reared was bimodal, with a group of large (Pseudacteon borgmeieri, Pseudacteon nocens, Pseudacteon obtusus and Pseudacteon tricuspis) and small (Pseudacteon cultellatus, Pseudacteon curvatus, and Pseudacteon nudicornis) species. P. borgmeieri was exceptional with respect to length of developmental time. Also reported are results of initial oviposition and developmental studies of some of these phorid species on other Argentinean Solenopsis ant species; P. curvatus was the only species able to complete its development on nonhost fire ants. These results support the concept of incorporating several complementary species of Pseudacteon in the biological control of pest fire ants.

Immature Development of <I>Pseudacteon tricuspis</I> (Diptera: Phoridae), an Endoparasitoid of the Red Imported Fire Ant (Hymenoptera: Formicidae)

Abstract Many approaches are being tested to control the red imported fire ant, Solenopsis invicta Buren. Biological control through the use of parasitoids and parasites is promising. Among the parasitoids of these ants, Pseudacteon spp. (phorid flies) are receiving special attention. One of these species, Pseudacteon tricuspis Borgmeier, has been released in target areas for field assessments. However, there is not enough information about their biology or interactions with their hosts. Here we describe the parasitization and development of P. tricuspis in two sizes of ants. We also evaluated the behavioral response of these ants to the attack of this fly. We found no difference in the development of P. tricuspis when attacking small or large ants. The immatures showed similar developmental time and morphology in both groups of ants. The egg is laid in the thorax, and there are three instars before pupariation. The first instar develops in the thorax, and it remains inside its serosa after hatching. It m...

Mechanisms of <I>Pseudacteon</I> Parasitoid (Diptera: Phoridae) Effects on Exploitative and Interference Competition in Host <I>Solenopsis</I> Ants (Hymenoptera: Formicidae)

I conducted a series of laboratory experiments to quantify the effects and elucidate the mechanisms by which Pseudacteon tricuspis Borgmeier phorid flies affect the exploitative and interference components of interspecific competition in host Solenopsis invicta Buren ants. In manipulative experiments, workers retrieved 50% less food in a foraging tray with phorids present, compared with an equidistant foraging tray with the same food resource but without phorids. The average number of workers actively foraging in the tray with phorids was significantly less than in the tray without phorids. There were no significant differences in either average worker size or average number of workers present at the food resource at the end of the trials in trays with phorids versus trays without phorids. In a control set of trials in which no phorids were added to either foraging tray, the size of foraging workers averaged over both foraging trays was significantly larger than in either the phorid or no-phorid tray of the manipulative experiments. This suggests that colonies can communicate the generalized presence of phorids in an area, which leads to a decrease in foraging by major workers. S. invicta workers retrieved an intermediate amount of food in the foraging trays of the control experiment compared with the phorid and no-phorid trays of the manipulative experiment. Moreover, the overall amount of food obtained in both foraging trays was similar for the manipulative and control experiments, suggesting that the S. invicta colonies were able to compensate for harassment by phorids by altering their foraging strategy, which resulted in no net loss of food retrieved. When S. invicta was paired with S. geminata (F.) in interference competition experiments, phorid flies had no effect on the outcome of interspecific interactions. Phorids did not appear to be attracted to host workers once they were engaged in combat with enemy workers, and the spatial distribution of fighting was significantly different than the spatial distribution of parasitization attempts.

Host-Specific Attraction of Pseudacteon Flies (Diptera: Phoridae) to Fire Ant Colonies in Brazil

Pseudacteon fly host-specificity tests were conducted in the field in southeastern Brazil with Solenopsis fire ants in the saevissima and geminata complexes. These parasitic flies showed a strong preference for fire ants in the saevissima complex. No Pseudacteon flies were attracted to three Solenopsis geminata (F.) colonies when they were set out in trays, but many flies were quickly attracted to three trays with saevissima complex colonies when they were set out between the S. geminata colonies. Even when both species of ants were placed together side by side, more than 99% of flies hovered over trays with saevissima complex ants. When all of the saevissima colonies were removed, leaving only the S. geminata colonies available, about 95% of flies flew away. Several flies, however, did transfer to the S. geminata colonies for a few minutes and at least one fly (P. wasmanni) attacked a few S. geminata workers. Altogether, 588 parasitized workers were collected from the saevissima complex colonies compared to 12 from the S. geminata colonies. Two hundred-sixty-two flies emerged from the saevissima complex colonies (52% Pseudacteon tricuspis Borgmeier, 39% Pseudacteon litoralis Borgmeier, 4.6% Pseudacteon wasmanni Schmitz, 2.7% Pseudacteon pradei Borgmeier, 0.4% Pseudacteon curvatus Borgmeier). No adult flies emerged from the S. geminata colonies. These results demonstrate that P. tricuspis and P. litoralis are highly specific to saevissima complex fire ants and strongly indicate that they would pose little threat to native fire ants should they be released as biocontrol agents for imported fire ants in the United States.

Fire Ants Attacked by Phorid Flies

Four species of the genus Pseudacteon (Diptera:Phoridae) were observed attacking fire ants in the Solenopsis saevissima complex (Hymenoptera:Formicidae). In descending order of frequency noted, the phorids were Pseudacteon pradei Borgmeier, Pseudacteon wasmanni Schmitz, Pseudacteon tricuspis Borgmeier, and Pseudacteon nudicornis Borgmeier. Two or 3 of the species were commonly taken at the same Solenopsis nest. The frequency of phorid attack on disturbed fire ants nests was several times greater than on undisturbed nests.