Fig 1. Description and representation of pollen trap systems used in this study.

(A) Front trap—FT: this is a small trap that is fastened to the front of a hive with the use of two small hooks and covering the existing entrance. The bees enter into the hive by walking on a metallic mesh that connects the pollen trap to the landing board of the hive. Round shaped holes of the trap strip pollen from bees with minimum damage. Pollen accumulates in a side opening drawer (not showed in the picture). They have the advantage of being easily removed, although their storage capacity is far lower than bottom and wall traps. (B) Wall trap—WT: it is a modified front trap. For its correct positioning it is necessary to apply a change to the natural flight opening of the hive: the latter is occluded with a metal sheet and replaced with three holes created especially in the area immediately above having a diameter of about 5 centimeters. On the new flight opening that is positioned at 2/3 of the beehive the trap will be then applied (for this reason is also called high trap). WT can be mounted on all type of hive and permits that pollen is recovered cleaner and less humid. (C) Bottom trap—BT: this trap is fixed on the bottom of the hive that need to be modified. Bees pass through a series of mesh screens, that remove the pollen from their rear legs. The pollen drops down through the screens into pollen drawer and can be harvested without opening the hive. This pollen trap can virtually occupy all the area of hive to promote good ventilation for dry pollen. The trap can be removed easily when not needed.