Biology of Trypoxylon in Trap Nests in Wisconsin (Hymenoptera: Sphecidae)

Abstract

Four species of Trypoxylon were collected in sumac trap nests in Wisconsin: T. frigidum Smith, rubrocinctum Packard, striatum Provancher, and tridentatum Packard, the latter being found in one nest only. Nests of each species consisted of a linear series of cells constructed in borings of 3/16-, 1/4- and 5/16-inch diameter. The average number of cells in nests of T. frigidum and rubrocinctum was about six. Nests of T. striatum averaged five cells, as the cells were longer. The mother wasp provisioned a cell with spiders, laid an egg on the abdomen of one of the last spiders introduced, and sealed the cell with a wall of clay, thus providing a microcosm with shelter and food for each of the prog- eny. A variety of spiders was utilized as prey; most nests contained at least three species, two genera and two families. Theridiid spiders were preferred by T. rubrocinctum, whereas striatum relied miostly on Araneidae. The amount of food in cells was determined primarily on a weight basis. The period of larval growth was about one week. After the larva spun a cocoon, most of the remaining period in the univoltine life cycle of T. rubrocinctum and striatum was passed as a prepupa in diapause. T. frigidum had a summer and winter generation, with the summer generation requiring about one month. Reared adults were asso- ciated with cell location in the nest, and no consistent pattern of sequences of sexes was shown. The nests were parasitized infrequently by Chrysis verticalis Patton, C. pellucidula Aaron, Melittobia chalybii Ash- mead, and miltogrammine sarcophagids in the genera Amobia and Senotaenia.