hover over ants (Wuellner et al. 2002). All flies were dead by the end of the 4 d trials.

After tests, ants were removed from the trays, retained in small boxes (20 by 12 by 5 cm)

with tight-fitting vented (2 by 3 cm) lids, and inspected for pupating flies every other day

for a period of 3 5 d. Inside each retainment box, I placed a small 3 cm block of moist

plaster and a nest tube with water held in the end by a cotton ball (16 by 125 mm). Ants

were fed fresh sugar water every 2 d. I removed dead workers from the small boxes and

placed them inside condiment cups (4 oz) with moist plaster bottoms where the larvae

could pupate. Determination of pupating flies in ant head capsules was made by looking

for a sclerotized cap flanked by two respiratory horns as described by Porter (1998a).

The total number of pupae produced in each ant species was divided by the fifteen to

twenty female flies used in the trials to produce an average pupae production rate per

female fly. Pupae were held for a total of 25 d to determine rates of adult emergence.

Paired preference tests

 Host preferences of Formosa P. curvatus flies were examined as paired difference

tests consisting of seven paired trials with S. invicta and S. xyloni (August-September

2002) and six paired trials with S. invicta and S. geminata (September 2002). Trials were

conducted in three white plastic trays (42 by 28 by 15 cm; Panel Control Corp., Detroit,

MI) with screened vents and tight-fitting glass lids. In the bottom of each tray, two long

side-by-side holes were cut and two smaller trays were glued (30 by 7 by 5 cm) as

described by Porter (2000). This configuration produced two parallel chambers in the

bottom of the big tray that allowed the testing of two species of ants at the same time.

Ants were contained in the two bottom trays by coating their sides with Fluon (AGC

Chemicals Americas Inc., Bayonne, NJ). To maintain high humidity, four moistened 3 by

3 by 4 cm sponges were placed in the corners of the test trays and a 1 cm thick layer of