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Hager & Kurczewski — Cleptoparasitism 
459 
stage of the developing wasp at the time of maggot deposition; eggs 
and young larvae were most vulnerable (Table 1). The two nests 
presumed parasitized that were attacked after an initial provisioning 
may have contained young larvae. 
In an attempt to test whether the female or the larva is responsible 
for the elimination of maggots after their introduction into a nest, 
four cells each containing a larva and maggot(s) were placed in 
individual rearing tins, thereby removing any influence the mother 
may have had on the cleptoparasitized nest. All of the maggots 
disappeared within hours, regardless of whether any extra prey were 
added to a cell. This suggests that the larva either starves the maggot 
indirectly by consuming the food or eats the maggot. One advantage 
of progressive provisioning in A. harti therefore appears to be the 
larva’s ability to outcompete the cleptoparasite. The mother’s ability 
to defend her larvae against cleptoparasitism may play a lesser role. 
Evans (1966, 1970) has noted in Bembix belfragei Cresson the co- 
occurence of larva and maggots, all of which were able to reach 
maturity by feeding on prey provided by the female. 
The total frequency of successful cleptoparasitism of used nests 
was 4.08%. If all of the provisioned nests found empty or with 
remains are considered to have been cleptoparasitized (which is 
highly unlikely), then 20% of the nests were cleptoparasitized. This 
is compared to the 57.9% S. vigilans parasitism of a mass provi- 
sioned Tachysphex terminatus (F. Smith), at the same site (Spof- 
ford, et al., 1986). Evans (1966) did not report any quantitative data 
on cleptoparasitic loads for progressive provisioning Nyssoninae 
but did note that cleptoparasitism was less than that for mass provi- 
sioned of this subfamily. Although cleptoparasitic frequencies for 
other wasps are scarce, the pattern still emerges that those species 
not exhibiting progressive provisioning suffer a higher clepto- 
parasitism — from 20% [Philanthus zebratus nitens Cresson (Evans, 
1970)] to 50% [ Sphecius speciosus (Drury) (Reinhard, 1929; Evans, 
1966)]. 
Behavioral adaptations other than the manner of provisioning 
may also reduce cleptoparasitism. Nests may be provisioned at 
times of the day or season different from the diurnal and seasonal 
activity patterns of the flies. Such rhythmical modification is not 
well documented. Evans et al. (1980) found Crabro monticola 
(Packard) and Crabro largior Fox bringing prey to their nests early 
