AN EXPERIMENTAL STUDY OF THE ATTRACTIVENESS 
OF ARTIFICIAL PERCH TERRITORIES TO MALE 
TARANTULA-HAWK WASPS, HEMIPEPSIS USTULATA 
(HYMENOPTERA: POMPILIDAE)* 
By William Matthes-Sears and John Alcock 
Department of Zoology, Arizona State University, 
Tempe, AZ 85287 
Introduction 
Males of the tarantula-hawk wasp Hemipepsis ustulata (Dahl- 
bom) defend perch sites on the highest points of prominent hills and 
ridges in central Arizona (Alcock 1979, 1981, 1983). A territorial 
male permits no other male to alight in his plant, be it a palo verde 
(Cercidium microphyllum ), jojoba bush ( Simmondsia chinensis), 
creosote bush ( Larrea tridentata), saguaro cactus ( Carnegia gigan- 
tea ), or cholla cactus ( Opuntia spp.). Receptive females sometimes 
visit a territory site; mating occurs when the resident male captures 
the female in flight and the pair descends to the ground for a brief 
copulation. Because defended plants contain no food or oviposition 
resource for females nor any nests from which virgin females may 
emerge, males of El. ustulata appear to practice lek territoriality 
(Alcock 1981); they defend areas whose only value to females is the 
presence of a mating partner. 
A striking feature of male behavior is the consistency with which 
individuals of different generations select certain perch trees from 
year to year. In one study site many dozens of palo verdes grow on 
the ridge and yet, every year over five flight seasons the same two 
trees have been most frequently occupied by territorial wasps 
(Alcock 1984). A few other trees are almost as popular while some 
are usually claimed for only a few days of the 2-3 month flight 
season. The wasps completely ignore the many other trees on the 
ridge. 
We have analyzed the properties of natural territories in order to 
determine why some trees are so much more likely to be defended 
than others (Alcock 1984). Males only defend palo verdes growing 
* Manuscript received by the editor April 18, 1985 
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