J. HYM. RES. Vol. 9(2), 2000, pp. 370-376 Load-lifting Constraints on Provisioning and Nest Building in the Carpenter Wasp, Monobia quadridens L. (Hymenoptera: Eumenidae) Paula K. Edgar and Joseph R. Coelho (PKE) Department of Instructional Services, John Wood Community College, 150 South 48th Street, Quincy, Illinois 62301, USA; (JRC) Department of Biology, Culver-Stockton College, One College Hill, Canton, Missouri 63435, USA Abstract. — The foraging and mud-carrying capacity of the trap-nesting carpenter wasp, Monobia quadridens L., was examined in relation to load-lifting ability. The body mass of caterpillar prey collected increased over the course of the season. Consequently, the ability of the wasps to carry prey became compromised late in the season. Caterpillar mass was not correlated with wasp size, but the mass of mudballs used in nest construction was related to wasp size. Wasp foraging may be constrained by the size of pyralid caterpillars available at any particular time, which changes because of caterpillar growth. Mudballs are constructed by the wasps themselves; therefore, wasps may be able to optimize mudball size in accordance with their own size, but mudballs were much lighter than caterpillars and never approached the upper limit of the wasps' ability to carry them. Optimal foraging theory suggests that an animal will experience increased fitness as it becomes more efficient at obtaining food or energy. One obstacle encountered by flying insects that carry food loads is the need to generate sufficient lift force to re-main airborne. Prey selection may be lim-ited by the size of the prey the insect can successfully carry while in flight. Marden (1987) demonstrated that maximum still-air lift force in flying animals depends primar-ily on flight muscle mass (M h J. A fixed minimum ratio of flight muscle mass to to-tal mass lifted, the marginal flight muscle ratio, is required for successful takeoff. An-imals with higher flight muscle ratios (FMR) have greater maneuverability, and should be better able to lift and carry loads, seize prey, avoid predators and vie for ter-ritories and mates (Marden 1987). Recent studies examining the relation-ship between maximum lift force and ac-tual load carriage in foraging and provi-sioning wasps have used ground-nesting species, including Vespula spp. (Coelho and Hoagland 1995), Sphecius speciosus Drury (Coelho 1997), and Sphex ichneu-moneus L. (Coelho and LaDage 1999). In the present study we investigate load car-riage during provisioning and mud-car-rying in Monobia quadridens L. (Hymenop-tera: Eumenidae), an aerial nester. Aerial nesting may apply additional constraints to load carriage. Two ground nesting species, the cicada killer (Sphecius speciosus) and the great golden digger wasp (Sphex ichneumoneus) are able to car-ry heavier loads than are theoretically pos-sible, primarily by climbing vegetation, then flying toward their burrows (Coelho 1997, Coelho and LaDage 1999). Although presumably using maximum power, such overloaded wasps can only descend. Ae-rial nesters lack this option, as the final flight to the nest requires a vertical take-off and ascent to the nest entrance. M. quadridens may not attempt to carry near-maximal loads if the load compromises flight maneuverability and nest entry. The carpenter wasp, M. quadridens, read-ily nests in old borings of carpenter bees, Xylocopa spp. (Tandy 1908, Rau 1935), and
BioStor
