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Assessing the toxicity of pesticides on bees: an INRA test adopted at the international level

Assessing the risk of pesticide use in agriculture is a key component in obtaining a marketing authorization for such products. In particular, tests that measure pesticide effects on non-targeted organisms such as bees are required. Scientists at INRA have developed a toxicity test on bee larvae, which was adopted in France in 2007.This approval was extended to the rest of the OECD countries on 26 July 2013.This is the first test on bee larvae where the exposure to the tested product is perfectly controlled.

. © INRA
Updated on 01/17/2014
Published on 11/19/2013

Pollinating insects, and especially bees, contribute greatly to the reproduction of many plants, both cultivated and wild. Preserving these insects is essential to maintain sustainable agricultural production systems and overall biodiversity.

As is the case with antibiotics, the arsenal of insecticides must be renewed constantly. New groups of substances make it possible to control pests that have either developed resistance to or are unaffected by older products. Meanwhile, new compounds are subject to increasingly stringent assessment tests required by the organisations that approve pesticides in France and in Europe.

A bee larvae test under controlled conditions

In response to requests from experts, scientists from INRA have developed a test on bee larvae under conditions where exposure to a pesticide is controlled, which was not the case for the previously accepted test. This standardized in vitro larval breeding method was designed to be easily transposable to the accredited laboratories responsible for pesticide assessments.

In practice, larvae collected from a hive are raised artificially in an oven. They are placed in plastic cups which imitate the honeycomb in a hive and receive a controlled diet based on royal jelly, sugars and yeast extract. They float in this semi-liquid nutrient medium, feeding at their own rate. The larvae develop as successfully using this feeding method as under natural conditions.

Larvae can easily be exposed to pesticides in nature by consuming nectar from contaminated flowers, but the quantities ingested cannot be measured. However, in vitro, the pesticide to be tested may be introduced in known concentrations into the nutrient medium. The larvae consume the contents of their cup each day, thereby making it possible to measure the dose of pesticide ingested.

The product can be evaluated for either chronic or acute toxicity during the six to seven days of larval life before development into a chrysalis. Mortality is detected from the immobility of larvae, followed by their rapid decomposition. Another advantage of the test is that it is possible to observe deferred effects on chrysalises and adults because some agents may not cause immediate effects but induce delayed mortality. This larvae test was developed using a reference insecticide, dimethoate, which is extremely toxic to bees, before then being used with several other compound groups.

A battery of tests, from the laboratory to natural conditions

The in vitro larvae test makes it possible to determine from what level a given product is toxic. It offers the best controlled conditions of exposure at a lower cost compared to other tests, such as those conducted in a greenhouse .It can also be used for the initial sorting of candidate compounds.

This test, accepted by the CEB(1) in March 2007, was submitted to the OECD, which has just adopted it as an acute exposure guideline. In the coming months, the chronic version will be the subject of a guide document and will be proposed as a guideline after a ring test.

(1) The Commission des Essais Biologiques is the French authority responsible for validating official test methods.

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Press Relations:
INRA News Office
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Plant Health and Environment
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