Biology of Osmia in Trap Nests in Wisconsin (Hymenoptera: Megachilidae)1

Abstract

Trap nests consisting of borings in wood blocks or sumac stems were used to study the biology of species of Osmia in Wisconsin. The borings were ¼ or 5/16-in. diameter and about 6 in. long. Six species of Osmia were found in the trap nests during the period 1952–62: lignaria Say, coerulescens (L.), albiventris Cresson, proximo Cresson, pumila Cresson, and tersula Cockerell. Partitions and plugs in nests of O. lignaria were made of clay, and triturated plant material was used in the nests of the other species. All species had 1-generation-per-year life cycles. Cells were made in nests and provisioned with pollen during June and July. A single egg was laid in each cell. The larvae grew rapidly and spun a silken cocoon of tough consistency prior to pupation. Adults normally were produced in August. These fully formed adults remained in cocoons during the winter and emerged the next spring. The sexes of O. lignaria were reared in a nearly equal ratio, but in the other species more females than males were reared. A few of the Osmia nests were parasitized by Leucospis affinis Say and Sapyga martini Smith.