Dag, A., Department of Horticulture, Faculty of Agriculture, Hebrew University, Rehovot 76100, Israel
Eisikowitch, D., Department of Plant Sciences, George S Wise Fac. of Life Sciences, Tel Aviv University, PO Box 39040, Tel Aviv 69978, Israel

Melons are grown in Israel in 'walk-through' tunnel greenhouses. We compared honey bee (Apis mellifera) foraging activity and melon nectar characteristics in well-ventilated and in closed greenhouses. Foraging activity in the open greenhouses was two- to five-fold greater than that in the closed greenhouses. This higher activity could be explained by higher flower attractivity due to a higher nectar sugar concentration both in hermaphroditic flowers and male flowers. The higher sugar concentration in the open, ventilated greenhouses was probably as a result of the relatively lower humidity there. The greater foraging activity in the open greenhouses also may have been due to lower air temperatures and better accessibility for the bees. It seems that greenhouse ventilation can improve honey bee pollination activity in melon and probably other greenhouse crops as well.