40 
Psyche 
[March 
role that the chemical plays in the mating system of Philanthus spp. 
is not possible; though some educated guesses can be made. The 
common occurrence of interactions between non-territorial and 
territorial males on the latter’s territory suggests that scent marking 
does not function to warn conspecific males that they are intruding 
at another’s perch, as commonly occurs in mammals (Shorey 1977) 
and in certain species of ithomiine butterflies (Pliske 1975). In fact, 
something to the contrary may occur. An intruding male could 
capitalize on the energetic investment of another male by usurping a 
territory on which a pheromone has already been applied (Alcock 
1975a). The advantage of the action depends upon the persistancy of 
the chemical. It also seems unlikely that the combined pheromone 
of all territorial males is equivalent to a lek, serving to attract 
females to the general area. Females chose the location based on 
requirements for nesting not because of the presence of the males. In 
P. triangulum (Simon-Thomas and Poorter 1972) and in P. zebratus 
where the territories are some distance from the nests, the function 
of the pheromone in attracting females is obvious. In P. psyche and 
P. bicinctus (Gwynne 1978) where the territories are within the 
nesting area the function is less obvious unless short range com¬ 
munication is useful. Alternatively or simultaneously the phero¬ 
mone may function as an aphrodisiac stimulating the female to 
copulate, as has been shown in a variety of insects (Butler 1970). 
Summary 
The general predictions made by Alcock (1975a) concerning the 
evolution of a territorial mating strategy in male sphecids are borne 
out in Philanthus psyche. That is, females are clumped in space in a 
manner which the males can predict and the potential territories are 
defendable by the males in terms of time and energy limitations. 
Males of P. psyche apply a pheromone to plants surrounding the 
territory. This is believed to attra.ct sexually receptive females. Male 
behavior associated with pheromone usage varies with respect to 
various ecological factors (e.g., wind speed, wind direction). As 
shown by a study of the “swirling flights” of males, this species 
shows true aggression, and thus, true territoriality. Pursuit behavior 
of the males functions in investigating intruders on the territory that 
may be potential mates and is not an aggressive response. 
