VIII SIMPOSIO INTERNAZIONALE ICPBR

HAZARDS OF PESTICIDES TO BEES

Bologna, 4-6 Settembre 2002

Apicidi e schemi di monitoraggio

Studies to improve the performance of dead honey bees collection traps for monitoring bee mortality

Claudio Porrini (1), Piotr Medrzycki (1) (2), Luca Bentivogli (1) and Giorgio Celli (1)

(1) Dipartimento di Scienze e Tecnologie Agroambientali, University of Bologna, via Filippo Re, 6 - 40126 Bologna, Italy. E-mail: cporrini@entom.agrsci.unibo.it
(2) Istituto Nazionale di Apicoltura, via di Saliceto, 80 - 40128 Bologna, Italy

The number of dead bees found in collection traps is an important criterion for estimating the hazards of pesticides to bees. In spite of this fact, the dead bee count through the use of this traps is underestimated because the number of dead bees lost in the field and during the return flight to the hive is not known. The solution would consist in having a continuous mode of monitoring by electronic devices, but the high cost of using these devices limits their application.

The dead bee collection traps are usually used in bio-surveys of pesticides pollution, where the mortality rate is controlled on a weekly basis. Our research group, with the aim of avoiding the dead bees disappearing from these traps due to predators, has been studying for some time, a different type of trap that may solve this problem. Such trap (named "barrier trap") applied directly to the hive’s entrance is divided into two parts. The upper one, a V shaped structure directly attached to the hive’s entrance, impedes the export of dead bees by the undertaking bees, forcing them to pass through 6.5 mm diameter holes 5 cm from the floorboard. This way the undertaking bees are obliged to carry the dead bees into the underneath section of the devise, designed to collect dead bees and allow the alive ones to exit, through the 6 mm holes.

Twelve hives were used in the experiment. Six were placed in a rich spontaneous botanical species area, a suitable refuge for a numerous small animals (complex environment), while the other six hives were placed in a cultivated area (simplified environment). Three hives from each area were fitted with the experimental traps "barrier traps" and other three with the "underbasket" cages, consisting of a wooden frame (50 x 100 x 10 cm) covered above and below with wire mesh. The top meshes had a hexagonal configuration with a side length of 2 cm and the bottom ones had rectangular with a 3 mm side length. The trials were carried out over two weeks in the Spring and Summer periods. The next trials will take place in Autumn. For each day of the trials, 20 dead bees marked with a different colour were introduced to each hive. The weekly count of dead bees per trap was made on the eighth day.

The average efficiency of the two traps, "barrier trap" vs. "underbasket", in the two environments, was respectively, for the Spring period, of 84.4% vs. 53.8% in the complex environment and 77.0% vs. 56.8% in the simplified environment. For the Summer period, the results were respectively: 88.1% and 29.5% in the complex environment and 77.4% and 4.8% in the simplified one.

This preliminary data allows us to forecast an efficient performance of the "barrier traps" in comparison to the "underbasket". Subsequent trials are being made to increase the devices’ application and efficiency.