Bijensterfte, oorzaken en gevolgen

A new scientific study that marked honeybees with radio-id chips to measure the impacts of ultra low dose of neurotoxic systemic insecticides on the flight behavior of honeybees found significant effects of the insecticide fipronil (marketed under the names Mundial, Goliath, Regent TS and produced by BASF) on the number of foraging flights and on the time to return to the hive.
The experiment was carried out in a outdoor tunnel (8 m x 20 m, 3.5 m high) covered with an insect-proof cloth (2 mm 9 2 mm mesh) and a ground covered with plastic. The distance between the hive and the sucrose syrup feeder was 18 meter.
The median lethal dose of fipronil is 6 nanogram per honeybee. In this experiments the bees were given a single one-time ultra low dose which is twenty times below the deadly dose: 0.3 nanogram fipronil per honeybee.
The researchers found that even this single ultra low dose significantly reduces the number of foraging trips of honeybees. They also observed that their time to return to the hive increased with 30 seconds. The percentage of bees returning within one minute reduced from 77% (no treatment) to 51% (0.3 ng fipronil per bee). Earlier studies (e.g. Yang e.a. 2008)where bees were marked with paint in stead of radio-id chips and counting and measuring was done by humans with stopwatches observing the bees at the hive and the feeder showed similar effects for imidacloprid. The radio-id chip method enables much more precise analysis of the so called sub-lethal (sub=below, lethal=deadly) effects of pesticides on pollinators.
In The Netherlands the systemic insecticide fipronil is authorised for seed coating and phytodrip in (Dutch crop names) Chinese kool, bloemkool, boerenkool, broccoli, rodekool, savooienkool, spitskool, spruitkool and wittekool to protect these cabbage crops to damage by the cabbage fly (koolvlieg), and for the elimination of cockroaches.
Fipronil is systemic, it enters the plantsap and contaminates pollen and nectar of treated plants and also of nearby growing wild flowers, trees, and weeds and contaminates water on which honeybees forage.

Honeybee tracking with microchips: a new methodology to measure the effects of pesticides
Axel Decourtye, James Devillers, Pierrick Aupinel, Francois Brun, Camille Bagnis, Julie Fourrier and Monique Gauthier, Ecotoxicology (2011) 20:429–437

ABSTRACT: Losses of foraging bees are sometimes attributed to altered flight pattern between a meliferous plant treated with an insecticide and the hive. Only a limited number of studies has investigated the impact of pesticides on homing flight due to the difficulty of measuring the flight time between the food source and the hive. Monitoring the flights of the foraging bees needs their individual identification. The number of bees monitored simultaneously and the time span during which observations can be made limit most of the monitoring techniques. However, techniques of automatic tracking and identification of individuals have the potential to revolutionize the study of the ecotoxicological effects of xenobiotics on the bee behaviors. Radio Frequency Identification (RFID) offer numerous advantages such as an unlimited number of codes, a large number of simultaneous recording, and a quick reading, especially through materials (e.g., wood).

The aim of this study was to show how the RFID device can be used to study the effects of pesticides on both the behavioral traits and the lifespan of bees. In this context, we have developed a method under tunnel to automatically record the displacements of foragers individualized with RFID tags and to detect the alteration of the flight pattern between an artificial feeder and the hive. Fipronil was selected as test substance due to the lack of information on the effects of this insecticide on the foraging behavior of free-flying bees. We showed that oral treatment of 0.3 ng of fipronil per bee (LD50/20) reduced the number of foraging trips. The strengths of our approach were briefly discussed.

Source: Ecotoxicology (2011) 20:429–437:
http://dx.doi.org/10.1007/s10646-011-0594-4

Zie ook:
De Pers 22 maart 2011 Pesticide brengt bijen in gevaar