VIII SIMPOSIO INTERNAZIONALE ICPBR

HAZARDS OF PESTICIDES TO BEES

Bologna, 4-6 Settembre 2002

Effetti dell’imidacloprid sulle api

Effects of sub-lethal imidacloprid doses on honey bees’ (Apis mellifera L.) homing rate and foraging activity

Laura Bortolotti (1), Rebecca Montanari (1), José Marcelino (2), Piotr Medrzycki (1) (3), Stefano Maini (3) and Claudio Porrini (3)

(1) Istituto Nazionale di Apicoltura, via di Saliceto 80, 40128 Bologna, Italy. E-mail: laurabortolotti@hotmail.com
(2) Departamento de Protecção Vegetal, Escola Superior Agrária de Castelo Branco, Qt Sra. Mércules, 6000 Castelo Branco, Portugal
(3)Dipartimento di Scienze e Tecnologie Agroambientali, University of Bologna, via Filippo Re 6, 40126 Bologna, Italy

The systemic insecticide imidacloprid, within formulations Gaucho and Confidor , is a molecule of the chemical group Chloro-nicotinyls. From several years reports by French and Italian beekeepers suggested a lethal effect of imidacloprid on honey bees; in particular the molecule has been related to honey bees mortality and decrease of hive population, affecting the orientation and ability of honey bees to return to the hive.

In this paper we investigate the effects of sub-lethal doses of imidacloprid (Confidorâ ) on foraging activity and homing ability of honey bees. For this purpose, honey bees from one hive were trained to forage on a feeder filled with a 50% sugar solution. The feeder was gradually moved up to a distance of 500 meters from the hive. Thirty bees, foraging on the sugar solution, were captured, individually marked with coloured number tags and settled in a flying cage. This group represented the control bees. The feeder was then replaced with a new one, filled with an imidacloprid supplemented sugar solution and thirty bees foraging on this feeder were captured, individually marked with different coloured number tags and settled in another flying cage. Three doses of imidacloprid were tested: 100 ppb, 500 ppb and 1000 ppb. Since the solutions with 500 ppb and 1000 ppb of imidacloprid had a repellent effect and caused the bees stop visiting the feeder, only 10 and 17 honey bees were captured for the two doses respectively. Knowing that imidacloprid effects start half an hour to one hour after the ingestion, bees were released from the flying cage 1 hour after the confinement. The behaviour of the bees was followed for 2 hours after the release: two persons at the hive and one person at the feeding point recorded the arrival and the departure of all marked bees. The presence of the bees at the hive and at the feeder was also recorded, for another hour, 5 and 24 hours after the liberation.

The results show that almost all the control honey bees returned to the hive starting again to visit the feeder between 2 to 5 hours after the release. Honey bees treated with the dose of 100 ppb could also return to the hive, but they restarted to visit the feeder only 24 hours after the release. Honey bees treated with 500 ppb and 1000 ppb completely disappeared after the release, and they were not seen during the following 24 hours, neither at the hive nor at the feeding point.