Range Expansion of Two Species of Pseudacteon (Diptera: Phoridae) in Alabama

L.C. ‘Fudd’ Graham1 and V.E. Bertagnolli1

Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama [1]

When fire ants were introduced into Alabama in the early 1900's, almost all of their natural enemies were left behind in South America (Jouvenaz 1990). As a result, fire ant densities are much higher in Alabama than they are in South America (Porter et al. 1997). Two species of imported fire ant occur in Alabama. The red imported fire ant, Solenopsis invicta, is located in the southern portion of the state and the black imported fire ant, Solenopsis richteri, is located in northwest Alabama.

Although the black imported fire ant was introduced into the United States before the red imported fire ant, its current range is thought to be northeastern Mississippi and northwestern Alabama. Vander Meer et. al. (1985) first detected a hybrid between the two species in Mississippi. The hybrid is thought to populate the northern tier of Alabama, Mississippi and Georgia .

One group of natural enemies that have shown some promise in the battle against fire ants are phorid flies (Figs. 1) in the genus Pseudacteon (Porter 2000). Currently, eleven populations of phorids have been successfully established in Alabama (Fig. 2). Pseudacteon tricuspis shows a strong preference for S. invicta and is established at seven sites in South Alabama. Pseudacteon curvatus shows a strong preference for S. richteri and the hybrid fire ant. It is established at four sites in North Alabama (releases in Madison and Lauderdale Counties by K. Ward).

Introduction

Materials and Methods

Releases of P. tricuspis and P. curvatus were conducted as described by Graham et al. 2003. The first successful release was in 1999 and new releases have been conducted yearly in different counties (Fig 2).

A release site and a corresponding control site approximately 9.5 km apart were selected in Macon and Talladega. In Houston, Lowndes, Walker and Cullman, these sites were ca. 32 km apart. Two plots were established at each site for bait stations and pit fall traps. Sampling areas for population data were set up in conjunction with each plot. Data collected in each sampling area were total number of mounds and mound size. At the Baldwin, Barbour, Marengo, and Tuscaloosa sites, Solenopsis spp. populations are monitored by counting mounds in three 0.1 ha circles near the control site.

Fig. 3 Fire ant population data from the first three phorid releases and

corresponding release sites

Graham, L. C., S. D. Porter, and V. E. Bertagnolli, 2003. J. Agric. Urban Entomol. 20(3): 165-171.Graham, L. C., S. D. Porter, R. M. Pereira, H. D. Dorough, A. T. Kelley, 2003. Fla. Entomol. 86: 334-339.Jouvenaz, D. P. 1990. In “Applied Myrmecology: World Perspective” pp. 620-627. Porter, S. D., Williams, D. F., Patterson, R. S., and Fowler, H. G. 1997. Environ. Entomol. 26 :373-84.Porter, S. D., 2000. Biol. Control 19: 35-47.Vander Meer, R. K., C. S. Lofgren, and F. M. Alvarez. 1985. Florida Entomol. 68:501-506.

References

Results

P. tricuspis reached the Macon control site in mid- to late-summer of 2000. P. curvatus were found approximately 1.6 kilometers north of the control site in Talladega in August 2002, but were not found south of the site until 2004. Flies from the Houston and Cullman sites have not been found at the control sites. Flies have not been found at the Lowndes control site, but have been found several miles past it.

Mound data are presented from the three oldest sites in Fig. 3. Droughts occurred in Alabama in 1999, 2000, and 2001. In addition, the coldest November and December on record were recorded in 2000. These environmental factors have influenced fire ant populations, as evidenced by the low number of mounds in May 2001 in Macon and reduction in mound numbers in 2001 and 2002 at the Talladega control site, where no phorids had been found at that time. Mound data in Fig. 4 are from release sites with no corresponding control.

Except for the Lowndes Co. release site (Fig. 3), mound numbers appear to be decreasing at each site where phorids have been released. Phorids are now present at all controls shown in Fig. 3 and mound numbers appear to be decreasing at these sites also.

The two Pseudacteon spp. released in Alabama have been recovered at eleven of twelve release sites and are spreading rapidly across the state and into Georgia (Fig. 5). These populations were mapped extensively during the 2004 field season. The ovals estimate the currently mapped ranges of the eleven populations (Fig. 5). The ranges of the Macon and Talladega populations are underestimates. We have not found the leading edges of these two populations.

P. tricuspis and P. curvatus have expanded their ranges to cover over 35,000 sq. miles in Alabama and Georgia . P. curvatus, which prefer S. richteri and the hybrid fire ant, are now moving into populations of S. invicta (see green squares, Fig. 5) and we expect to find P. tricuspis on hybrid fire ant populations soon.

Even though it appears that the phorid flies may have affected the fire ant populations at these sites, further study will be required to determine if these population reductions are permanent and due to the flies and not other factors.

Sites in the area where P. curvatus and P. tricuspis now coexist have been monitored since 2003, when no flies were present. Hopefully, the presence of more than one species of these parasitoids in an area will reduce fire ant numbers more dramatically and permanently than the reductions seen in Figs. 3 & 4 above and we will be able to document the reduction in fire ant mounds.

Acknowledgements

The authors wish to thank S. D. Porter, USDA-ARS, CMAVE, R. K. Vander Meer, USDA-ARS, CMAVE, J. T. Vogt, USDA-ARS, BCMRRU, A. Callcott, R. Weeks, and D. Roberts, USDA-APHIS, H. Dorough, C. Mason, D. Daniels, M. Faver, R. Hudson, D. Cain, K. Tucker, C. Pinkston, M. Mobley and K. Flanders, Ala. Coop. Ext. Sys.

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Fig. 5 Range of Pseudacteon and Solenopsis spp. in Alabama

Photo courtesy of S. Bauer

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Fig. 4 Fire ant population data from release sites only. First data point on each graph corresponds with phorid

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