Sequential size assessment and multicomponent decision rules mediate aerial wasp contests

In aerial conflicts among territorial insects, injury costs are not obviously high and contestants cannot physically ‘force the issue’. Resource-holding potential in these cases usually relates to morphological and/or biophysical determinants of flight performance and endurance rather than traditional parameters such as size and strength. However, success is sometimes related to body size. Males of the landmark-defending wasp Hemipepsis ustulata compete via elaborate noncontact aerial duels in which large individuals enjoy an advantage. We evaluated the hypothesis that size is important because of a correlation with high-performance flight. We used a residency manipulation to establish 92 escalated contests in which some individuals had the outer 16–18% of their forewings removed to reduce flight performance (independently of body size). Initial residents won most (78%) contests, but logistic analysis indicated that no other parameter, including size, wing treatment and age, could explain the pattern of contest outcome. Survival regression analysis implicated size, age and site location, but not wing treatment, as significant predictors of nonresident contest persistence. We also found evidence of assessment of relative body size. Since our wing treatment had no measurable effect, the importance of body size does not appear as an emergent property of a system in which contest ability is determined primarily by flight performance dynamics. We conclude that aerial contests in H. ustulata are mediated by complex multicomponent decision rules, in which contest role, relative body size, age and perception of resource value collectively determine a contestant's persistence time.