Exposure to Sublethal Doses of Fipronil and Thiacloprid Highly Increases Mortality of Honeybees Previously Infected by Nosema ceranae

ABSTRACT: The honeybee, Apis mellifera, is undergoing a worldwide decline whose origin is still in debate. Studies performed for twenty years suggest that this decline may involve both infectious diseases and exposure to pesticides. Joint action of pathogens and chemicals are known to threaten several organisms but the combined effects of these stressors were poorly investigated in honeybees. Our study was designed to explore the effect of Nosema ceranae infection on honeybee sensitivity to sublethal doses of the insecticides fipronil and thiacloprid.

Ultra low dose of systemic insecticide fipronil impairs foraging behavour of honeybees

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.

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