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Drone surrounded by worker bees. © INRA, MORISON Nicolas

Scientists flying to the rescue of bees

Pesticides under examination by researchers

A carpet of dead honey bees in front of a hive, resulting from their exposure to insecticides: that is a hard-hitting image.  But such massive poisoning episodes are not the principal concern among researchers. At present, in INRA's laboratories, they are focusing more on identifying the sublethal damage that follows exposure to low doses of plant health products. At low doses, these agents do not always cause the immediate death of insects, but they may compromise the survival of a colony. If, as is thought by most scientists, the decline of honey bees is also linked to pesticide use, it is undoubtedly these effects, which are so difficult to measure, that are the problem.

Updated on 03/27/2017
Published on 05/01/2014

Small doses, major effects

Even when subjected to low doses of pesticides, bees can exhibit a variety of disorders. For example, they are less able to learn or retain information. Their communication is also affected: the bees make more frequent mistakes when they need to indicate the distance and direction of a food source. Other sublethal effects of pesticides observed by INRA researchers include poor coordination when beating their wings and an impaired ability to maintain a constant body temperature. Abnormalities in larval development have also been seen, even at extremely low doses.

Damage to antennae

Antennal sensilla of a bee seen under a scanning electron microscope. The antennae of the bee are crucial to its perception of the environment (olfactory, tactile, chemical, etc.). © © INRA, BORNARD Isabelle / COLLET Claude
Antennal sensilla of a bee seen under a scanning electron microscope. The antennae of the bee are crucial to its perception of the environment (olfactory, tactile, chemical, etc.) © © INRA, BORNARD Isabelle / COLLET Claude
As well as having effects on bee behaviour, INRA scientists are studying the cell and tissue damage caused by low doses of insecticides. Work on the neurons in bee antennae has shown that exposure to certain insecticides can cause neuronal hyperactivity that is likely to disturb their senses of smell and touch and their susceptibility to pheromones. The consequences of these disturbances are notably being studied in the context of a Franco-Canadian partnership (ANR BEE-CHANNELS). By looking at their effects at a cellular level, scientists hope in the long term to be able to contribute to predicting the impact of pesticides on the physiology of honey bees before these agents are put on the market.

Treatment during flowering. © © INRA, MORISON Nicolas
Treatment during flowering © © INRA, MORISON Nicolas

Pesticides despised and banished

The use in France of Gaucho on sunflower seed was banned in 1999. In 2004, this ban was extended to maize. In the same year, the use of Regent on all seeds was in turn banned. In 2013, three compounds in the neonicotinoid family, including thiamethoxam, the active substance in Cruiser, were targeted by the European Commission. A two-year moratorium will prohibit their use as from the end of 2014 in the treatment of seeds and soils. These so-called systemic insecticides have been found in both nectar and flower pollen, and then in products from the hive.

Bee equipped with its RFID chip © MAITRE Christophe

Bees disorientated by a pesticide

One particular experiment made a major contribution to the moratorium on Cruiser: an INRA team, working in collaboration with ACTA, ADAPI and CNRS, fixed RFID chips on 650 foraging bees that had ingested low doses of thiamethoxam. These chips recorded their exits from, and entries into, the hive. The bees were then released 1 km away from the hive. The result was that the rate of non-returns among intoxicated bees proved to be two to three times higher than normal. This rate would be sufficient to destabilise a colony, or even lead to its collapse.

Test to evaluate the impact of pesticides on bee larvae © AUPINEL Pierrick

Testing new pesticides

The INRA Entomology Experimental Unit (Nouvelle-Aquitaine - Poitiers Research Centre) has developed a test that can evaluate the impact of pesticides on bee larvae. Reared under controlled conditions in plastic cells, the larvae are fed manually. Two types of pesticide exposure are possible with this test: an acute mode, which corresponds to a high dose delivered once, and a chronic mode, with lower doses repeated over time. Adopted by the OECD, this test is notably able to evaluate the deferred effects of compounds that are trying to obtain a marketing authorisation. The research team also focused on the effects of pesticides on development of the hypopharyngeal glands; in nurse bees, these organs secrete royal jelly, a substance that is essential to the diet of a brood.