Range Expansion of Two Species of

1
Fig. 1
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
Fig.2.
Photo courtesy of S. Bauer
Introduction
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).
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.
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.
Fig. 3 Fire ant population data from the first
three phorid releases and corresponding release
sites
Fig. 5 Range of Pseudacteon and Solenopsis spp.
in Alabama

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