Nesting biology of Japanese leaf-cutter bee, Megachile humilis Smith (hymerioptera, megachilidae)

Abstract

Megachile humilis SMITH is a common univoltine species, occurring mainly from late July to mid September in Japan. Nine nests were examined over 23 years. They are always found in shallow underground burrows, 4.9-12 cm long and 8-12 mm diameter. One discovered nest burrow (Hu-6) was in an abandoned tunnel of a spider, Atypus karschi DOENITZ, but all others had been excavated by the bees themselves. In completed nests, the burrow entrance is not plugged by leaf pieces, soil or other materials, but is always left open. The number of cells per nest is small, ranging from 1-3 (mean 1.6). Leaf pieces of cells are not stuck together using mandibular substances secreted by the bees; this is a unique feature of Megachile. The number of leaf pieces per cell ranged from 24-56 (mean 37.8). The shapes of leaf pieces used in different parts of cells are similar to those in other Megachile species, except for the semiround leaf pieces (A-3 type) at the cell bottom. This is not known in other soil-burrowing Megachile species. The provisions, eggs and cocoons of the M. humilis are the same as those of other known Megachile species.