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A toxicity test developed by the experimental unit of Entomology on bee larvae is adopted at the international level

Assessing the risk of pesticide use in agriculture is an essential component in obtaining a marketing authorization for these products.
The experimental unit of entomology has developed the first toxicity test on bee larvae which was adopted by France in 2007. This approval has been extended to the 34 OECD member countries on 26 July 2013. This is the first test on bee larvae where the exposure to the product under investigation is perfectly controlled.

Larves d'abeilles élevées in vitro pour tester des pesticides de façon parfaitement contrôlée. Unité expérimentale d'Entomologie, Poitou-Charentes © Armelle Pérennès
By Inra press service - Inra Poitou-Charentes communications department
Updated on 12/20/2013
Published on 11/28/2013

In response to these demands from experts, scientists have developed a test on bee larvae under conditions where exposure to a pesticide is controlled. This standardized, in vitro larval breeding method is designed to be easily transposable to the accredited laboratories responsible for pesticide evaluations.

A standardized breeding bee larvae

In practice, larvae collected from a hive are raised artificially in an oven. Placed in plastic cups which imitate the honeycomb in a hive, the larvae receive a controlled diet based on royal jelly, sugars and yeast extracts. They float in this semi-liquid nutrient medium and feed at their own rate. Using this feeding method, the larvae develop as successfully as under natural conditions where nurse bees deliver around 1300 small doses of food to them every day.

A controlled larvae exposure to pesticides to test

Under natural conditions, larvae may be exposed to pesticides by ingesting nectar from contaminated flowers, but the quantities ingested cannot then be measured. However, in vitro, the pesticide to be tested can be introduced in known concentrations into the nutrient medium. The larvae consume the contents of their cup each day (approximately 30 microlitres of medium), thus making it possible to measure the dose of pesticide ingested.

The product can be tested during the 6 to 7 days of larval life before development into a chrysalis. Mortality is detected from the immobility of larvae, followed by their rapid decomposition within around one hour. 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 test on larvae was developed using a reference insecticide, dimethoate, which is extremely toxic to bees.

A battery of tests, from the laboratory to natural conditions

The in vitro test on larvae makes it possible to determine, for a given product, the dose above which it is toxic to exposed larvae. This in vitro system offers the best controlled conditions of exposure, at a lower cost. It could be used for the initial sorting of candidate compounds.
This test, accepted by the CEB (Commission des Essais Biologiques) in March 2007, was submitted to the Organization for Economic Cooperation and Development (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.

OEDC (2013), Essai n°237 : Essai de toxicité larvaire chez l'abeille domestique (Apis mellifera), par exposition unique

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