Consistency in the relative attractiveness of a set of landmark territorial sites to two generations of male tarantula hawk wasps (Hymenoptera: Pompilidae)

Abstract

Males of the tarantula hawk wasp Hemipepsis ustulata defend conspicuous palo verde trees on mountain ridges. A comparison of data from two flight seasons (1981 and 1980) reveals that the preference rankings of males for a set of perennial territories on one ridge remained highly consistent from generation to generation. This is the first thoroughly documented demonstration for insects that landmarks used as mating encounter sites retain the same relative attractiveness from year to year. The stability of male preferences is indirect evidence that access to females is related to the ability to acquire high-ranking territories. Moreover, in both years, (1) the flight season was 2.5 to 3 months long, (2) the range of body sizes in this highly variable species remained the same, and (3) the ratio of territorial males to non-territorial patrollers was constant. A key difference was a strong reduction in the total number and density of males found in the study site in 1981. The wasps responded to the decrease in competition for perch territories by failing to occupy some low-ranking sites that were taken in 1980.