28 
Psyche 
[March 
to answer this, I measured the distance pursued by a male when 
possible to identify the intruder. Distance pursued refers only to 
those encounters in which males chased an insect that flew straight 
through or adjacent to the territory. It does not include swirling 
flights in which the intruder’s response would complicate measure¬ 
ment of the resident’s response. If the response was a simple 
instantaneous approach, the encounter was given an a priori value 
of 20 cm since this approximates the radius of the territories. The 
male did not make contact with the intruder in mid-air as occurs in 
other territorial sphecids (Lin 1963, Alcock 1975a, Gwynne 1978) 
except in a few cases where conspecific females were grappled at the 
end of a flight. For two hundred forty-seven responses to intruders 
of thirteen different species (minimum of seven per species), I was 
able to record the pursuit distance. Many more encounters were 
observed, but could not be recorded either because the distance or 
the identity of the intruder could not be accurately determined. The 
responses to conspecifics were differentiated into female, male, and 
female with prey. Gwynne (1978) has carried out a similar analysis 
with P. bicinctus using distinct levels of behavior (approach, butt, 
grapple and grapple to ground, in increasing order) as a measure of 
response intensity. The intruder species can be used as “natural 
models” of female conspecifics and one may compare the intensity 
of response to the degree of similarity to the female. Figure 3 shows 
the mean distance pursued for each type of intruder. If we compare 
these distances to a list of characteristics of each type of intruder 
(Table 1) we see that the degree of similarity to the female is roughly 
positively correlated with the intensity of response of the male. 
There is at least a rough relationship with response intensity 
(distance) for all characteristics considered, so it is difficult to 
determine to which the male responds and which are most impor¬ 
tant. 
As with P. bicinctus the response is greatest towards the females 
not carrying prey. The response to females ranged from 1.4 to 4.0 m 
(N = 13 - mean = 2.45 m). Several times it terminated with the male 
pouncing upon the female. The response to males averaged much 
[ ess (N =13; mean = 1.37 m; range 1.0 to 2.0 m; t-test for difference 
between females and males significant, p < .0001) but the attribute 
responsible for this difference was not distinctly discernable.. Ap¬ 
parently some subtle difference between male and female flight 
characteristics is sufficient to elicit responses of different intensities 
