Biology of Rygchium foraminatum in Trap-Nests in Wisconsin (Hymenoptera: Vespidae)

Trap-nests consisting of holes bored in sumac stems were used to study the nesting biology of R. foraminatum (Saussure) in Wisconsin. Typical nests consisted of a linear series of provisioned cells and empty spaces separated by clay partitions. The means of the lengths of cells ranged from 14.9 to 17.1 mm, and those of the spaces 6.2 to 7.9 mm, depending upon the diameter of the hole (6.25 mm or 7.8 mm) and the summer or overwintering generation. One hundred and fifteen summer generation nests had a mean of 4.45 provisioned cells; 25 overwintering nests had a mean of 4.76 cells. The cells were provisioned with caterpillars in the Gelechiidae, Oecophoridae, Olethreutidae, Pyralidae, Pyraustidae, Thyridae and Tortricidae. The sex and size of reared wasps were associated with the amount of provisions and the size of cells. The first-made cells normally were larger and contained females. The nesting behavior involved a sequence of egg laying, cell provisioning and partition construction. Customarily, an empty vestibule was provided at the terminus of the hole, and the exit orifice was securely closed with a thick plug of clay. The wasp larvae fed voraciously on the caterpillar provisions and grew rapidly. There were 5 larval instars. The mature larva spun a thin cocoon, voided its meconium, and entered a quiescent prepupal stage. Summer generation larvae proceeded to pupate and emerge as adults, but the overwintering generation larvae entered diapause and passed the winter in the prepupal stage. Under field conditions the egg stage lasted 2 or 3 days, the. larva matured in 6 or 7 clays, the prepupal stage was 4 or 5 days, and the pupal stage took 10 to 12 days.