30 
Psyche 
[Vol. 87 
Discussion 
The most efficient strategy for O. sericeus females appears to be to 
allow males to copulate, thereby minimizing the total energy and time 
spent in the interaction. The size of the nest area, density of nests, and 
the operational sex ratio probably greatly influence the quantity and 
intensity of male-female interactions. In order to better understand 
possible selective forces acting to bring about nest guarding in 
Oxybelus, comparison will be made with other nest guarding 
sphecids (Table 2). Wasps that have males associated with the 
parental nest (e.g. Microstigmus, Philanthus and Cerceris) are 
excluded here, but twig, cavity and mud nesters are included in Table 
2 mainly to suggest that such interesting wasps deserve further study. 
Males in some species cue in on provisioning females. These males 
patrol and also perch next to active nests, though not associating with 
any particular nest. For this to evolve requires that females remain 
receptive throughout the nesting cycle. For a male the advantage 
would be in the increased probability of his sperm fertilizing the egg, 
assuming sperm precedence which is well documented in other insects 
(see Lefevre and Jonsson, 1962; Boorman and Parker, 1976; Smith, 
1979). Gillaspy (1962) found males of Sphex trepanecus Saussure to 
cue in on provisioning females. When a prey-laden female approached 
her nest a male would appear and copulation occurred near the nest. 
The crabronine genus Lindenius commonly has males searching and 
entering nest entrances and Miller and Kurczewski (1973) hypothesized 
that such “nest searching” behavior may help reduce cleptoparasitism 
(by miltogrammine flies and chrysidid wasps) in dense aggregations. 
Oxybelus emarginatus normally has males patrolling nest areas but 
Krombein (1964) once found males in Florida not only patrolling and 
perching but also mounting and copulating with provisioning 
females. One of us (AWH) recently briefly observed the same 
behavior in O. emarginatus near Mission, Texas, only no copulations 
were observed. This ability to cue in on provisioning females 
probably developed early in the evolution of nest guarding. 
The transition from the ability to intercept provisioning females to 
establishment of territories in the nesting area seems a logical step. In 
Sphex cognatus Smith (Ribi and Ribi, 1980) and Tachysphex species 
(Kurczewski, 1966) males are known to maintain territorial stations 
in nesting areas and copulate with nesting females. In several other 
species male territories always include at least one female nest. These 
