Sex control by bees: a voluntary act of egg fertilization during oviposition.

The alfalfa leaf-cutter bee, Megachile rotundata, stops abdominal contractions briefly during oviposition of female eggs but not during oviposition of male eggs. Sperm stored in the spermatheca probably is pumped onto the micropyle of the egg during this pause. The stimulus inducing fertilization seems to be associated with the depth of the nesting tunnel.