Abstract
Foraging behaviour and pollinating efficiency of Osmia cornuta females (Oc) and Apis mellifera nectar [Am (N)] and pollen-nectar [Am (P)] foragers were studied in an orchard of young late-flowering almond tress in 1989 and 1991. Contact between the body of the pollinator and the stigma of the flower occurred in 98.7% of Oc visits, in 76.3% of Am (P) visits, and in 39.5% of Am(N) visits. Oc visited more flowers per unit time and fewer flowers per tree than either Am (P) or Am (N). In 1991 Oc flew longer distances and changed rows more frequently than Am. Fruit-set in flowers that received only one visit by one of the three pollinators examined in 1989 and 1991, respectively were as follows: 21.8% and 38.1% for Oc, 16.7% and 26% for Am (P), and 9.1% and 0% for Am (N). Pollinating efficiency of Am (P) does not appear to be limited by the quantity of compatible pollen on the body of the bee, but rather by the frequency of contact with the stigma of the flower.
