Honey bee brood ring-test: method for testing pesticide toxicity on honeybee brood in laboratory conditions

The Experimental unit of entomology (INRA, France) developed a new in vitro method to assess effects of pesticides on honey bee larvae. The method consists in rearing bee larvae in plastic cells. The larvae are fed with diet containing 50% of fresh royal jelly and 50% of an aqueous sugar and yeast extract solution, and reared in an incubator at 35 °C and 96% relative humidity. According to that method, 9 tests (7 in 2008 and 2 in 2005) were carried out in 7 laboratories and different countries. The objective of these trials was to assess the LD50 for dimethoate 48 hours after an acute exposure. The LD50 values ranged from 1.5 μg a.i./larva to 8.8 μg a.i./larva, with 2 tests with particularly high values (5.0 and 8.8 μg a.i./larva). In 7 tests, these values ranged from 1.5 μg a.i./larva to 3.1 μg a.i./larva. Such variability may be due to the colony origin, the season and larva heterogeneity at grafting. Solutions are proposed to improve the method through the continuation of the ring test.