Diurnal patterns of ovipositional activity in two Pseudacteon parasitoids (Diptera: Phoridae) in Alabama

1
Diurnal patterns of ovipositional activity in two
Pseudacteon parasitoids (Diptera Phoridae) in
Alabama L.C. Fudd Graham and Vicky E.
Bertagnolli Department of Entomology and Plant
Pathology 301 Funchess Hall ? Auburn University,
Auburn, Alabama
Results
Introduction
Two species of phorid fly are currently
established Alabama. Pseudacteon tricuspis is
established at five sites on populations of the
red imported fire ant, Solenopsis invicta, and
Pseudacteon curvatus is established at four sites
on populations of a hybrid fire ant (S. Invicta x
Solenopsis richteri). In South America, several
species of Pseudacteon are often found at the
same site and exhibit at least three behaviors
that help explain how resources are partitioned
(Porter 1997). Species attack different size
fire ant workers (Morrison et al. 1997), select
different periods of diurnal activity (Pesquero
et al. 1996) or attack fire ants engaged in
different activities (Orr et al. 1997). Phorids
that have been introduced into fire ant
populations in Alabama have no competition from
other phorid species. We documented the diurnal
activity of the two species of phorid fly that
have been introduced into Alabama and that,
currently, have no competition from other phorid
species that attack fire ants.
Fig 1. Daily activity patterns of P. tricuspis
on six collection dates in Macon County Alabama.
Fig 2. Mean daily activity patterns of P.
tricuspis in Macon County Alabama.
Materials Methods
The first release of P. tricuspis was in Macon
County in 1999 and the first release of P.
curvatus was in Talladega County in 2000. The
flies have spread over 50 km and 24 km,
respectively, from each site. Ants used in the
study were collected from the vicinity of these
original release sites just prior to field data
collection. Ants from four mounds per site were
returned to the lab and were separated from the
soil so clean colonies could be used for the
field data collection. Mounds were placed into
individual 52 x 40 x 13 cm trays lined with
Fluon. Upon arrival at the field site, air and
soil thermometers were placed near the collection
site. The four trays of ants were placed in
shady areas of the release sites approximately 8
m apart. The four trays containing ants were
agitated by shaking the tray. This was done to
induce pheromone release by the ants in order to
attract phorid flies. Thirty minutes after
agitation, phorid flies were aspirated out of
their tray using a double chambered aspirator
unit until no flies could be observed in the
tray. The flies were transferred from the
aspirator to a small plastic holding container
via a hole in the lid. CO2 was introduced into
the holding container to induce fly knock down.
Upon knock down, the lid was removed from the
container and flies were counted. After fly
count, the container was placed in the shade to
allow for fly recovery. The tray was again
shaken to agitate the ants and collection moved
to the next box. The collection process is
repeated every 30 minutes until flies cease
coming to the trays. Air temperature, soil
temperature and humidity were also recorded
every 30 minutes.
Fig 4. Mean daily activity patterns of P.
curvatus in Talladega County Alabama.
Fig 3. Daily activity patterns of P. curvatus
on six collection dates in Talladega County
Alabama.
Mean daily activity patterns for P. tricuspis
were similar to those found by Pesquero et al.
(1996) in Brazil, with mean peak activity
occurring during mid-day. In Brazil, activity
was greatly reduced 12 hours following sunrise.
However, P. tricuspis were still active in
Alabama at this time (ca. 6 p.m.), extending
ovipositional activity into hours when
Pseudacteon litoralis is usually active in Brazil
(Pesquero et al. 1996). Peak activity for P.
curvatus occurred later in the afternoon 1011
hours following sunrise, but moderate activity
was observed from four to twelve hours past
sunrise. Dates on graphs in Figs. 1 3 where
collection of phorids is zero sometime during the
day are dates when rain showers occurred during
the collection period and phorids could not be
collected because trays had to be covered.
References
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