Studies on the Seed Production of Alfalfa by Using the Wild Bees : I. Nest structures of Megachile (Eutricharea) rotundata (FABRICIUS) and damage of leaf cuttings by the founding bees

Abstract

Alfalfa leaf-cutting bee, Megachile rotundata was introduced from Idaho, U.S.A., in an attempt to utilize it as a pollinator of alfalfa in Japan. The rearing of this species was conducted in a cage tent (7m×10m×2m) setting up in a large green house, and alfalfa plants were supplied as pollen, nectar, and leaf sources. As the nesting materials, the three sizes of bee straws (4.0mm×8.0cm, 5.0mm×8cm, and 5.5mm×8cm) and the grooved boards (6mm×10cm) were used. The purpose of this paper is to clarify the damage of leaf cuttings by the founding bees. 1. Two sizes of elongate leaf pieces, viz. the large (A-1) and the small (A-2) were used for the cup of provisioned cells and the circular ones (B-1) for the cap of provisioned cells. A closing plug was composed by the small elongate (C-1) and the circular leaf pieces (C-2), but the former exceeded greatly in number. 2. The average number of leaf pieces used for the nest construction is tabulated as follows: [table] 3. The average dimension and weight of each type of leaf pieces are tabulated as follows: [table] 4. According to Tirigari (1963), the number of eggs oviposited by one alfalfa leafcutting bee was 12〜52 (mean 28). If one female made total 28 provisioned cells by using 4 bee straws of 5mm×8cm, she needs total 476 leaf pieces. The total weight of these leaf pieces corresponds to 1.0456g. In the United States it is noted that 1, 000〜2, 000 bees per acre should be enough for excellent pollination. If we kept the above number of bees and each bee made 28 provisioned cells during her. life-span, they would collect more than 1kg of leaf pieces for the construction. 5. Judging from the above estimation, the damage of leaf cuttings by the founding bees seems to be quite slight. Besides, the fact that this species is found to collect the etiolated leaf pieces is taken in account, the actual damage may be disregarded.