1985] 
Hager & Kurczewski — Cleptoparasitism 
453 
The cleptoparasitic behavior of S. vigilans was divided into two 
categories: (1) landing on the prey and (2) entering nests. A. harti's 
response to the presence of this fly was observed and classified as: 
(1) no response (wasp continued to normally provision the nest) or 
(2) response (wasp deviated from her normal provisioning pattern). 
We observed the following responses: (1) freeze-stop (Alcock, 1975), 
(2) flight, (3) prey abandonment, and (4) nest cleaning. 
Nests suspected of being parasitized were excavated within 24-48 
hr of the observed fly activity and the rates of parasitism deter- 
mined. Wasp larvae and fly maggots were removed from nests and 
placed in sand-filled, plastic 35 mm film canisters to simulate the cell 
environment. Larvae and maggots were fed quiescent caterpillars 
taken from provisioning females or obtained from nearby vegeta- 
tion and killed by freezing. Overwintering puparia and cocoons 
were placed in perforated containers in a punctured bucket (to allow 
drainage) and buried in the sand at approximately the mean cell 
depth of A. harti. The bucket was removed in March and brought 
into the lab to obtain emergence records. 
Results 
Phrosinella aurifacies 
P. aurifacies was most active during June and July in association 
with the first generation of A. harti (Fig. 1). There was a sharp 
decline in P. aurifacies activity as the season progressed (ANOVA 
F = 12.43, 14 df, p < 0.01, r 2 = 0.45). A few flies were observed 
sporadically in August and September. Daily activity of P. aurifa- 
cies during the first generation of A. harti was uniformly distributed 
(Fig. 2). 
P. aurifacies was observed walking circuitously on the tumuli of 
A. harti nests. The flies investigated any disturbed sand areas, 
including entrances to other wasp nests and footprints. No larvipo- 
sition was observed in an A. harti nest entrance or in or on the 
tumulus, nor were any maggots or puparia found in or near the cell 
of an excavated nest. Only one fly was observed exiting an open A. 
harti nest. When dug the next day, the cell of this nest was empty 
and no evidence of flies was found in its vicinity. A. harti occasion- 
ally chased away flies circling on tumuli of nests under construction. 
The abundance of P. aurifacies during the first generation coin- 
cided with the construction of the deepest A. harti cells. Regression 
