NESTING BIOLOGY OF JAPANESE LEAF-CUTTER BEE, MEGACHILE HUMILIS SMITH (HYMENOPTERA, MEGACHILIDAE)

Megachile humilis SMITH is a common univoltine species, occurring main ly 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 al l others had been excavated by the bees themselves. In completed nests , the burrow entrance is not plugged by leaf pieces, soil or other mat erials, 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 toge ther using mandibular substances secreted by the bees; this is a uniqu e 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 t he semiround leaf pieces (A-3 type) at the cell bottom. This is not kn own in other soil-burrowing Megachile species. The provisions, eggs an d cocoons of the M. humilis are the same as those of other known Megac hile species.