22.214.171.124. Level of exposure
An important issue in field studies is to demonstrate that all age cohorts of bees (forager and in-hive bees), have been exposed to the test pesticide at the level from which we want to protect them when considering the worst case exposure scenario. For spray products, three exposure routes should be considered: oral, contact and inhalation. Honey bees can be exposed orally through nectar, pollen, and water but also directly during flight or when walking on contaminated substrates. These exposure routes should be considered both for forager and in-hive bees, even if in-hive bees are exposed mainly through residues in the food. The contact and inhalation exposures for in-hive bees should be assessed only in certain cases (e.g. fumigant and liposoluble products with high wax-affinity).
In order to determine if the experimental conditions in the field tests allow one to achieve the target exposure level, several observations and analysis should be performed. For forager bees, the level of exposure can be assessed by observing the number of bees on the test crop, the number of bees entering the nest with pollen loads and the flight activity (e.g. counting the number of bees exiting from the nest in 30 seconds (Porrini, 1995). Confirmed contact with the treated crop can derive from the palynological analysis of the pollen load (see Delaplane et al., 2013a). Pesticide residues should be analysed in honey bees, as well as in the plant matrices (nectar, pollen and guttation droplets) and in the hive (honey, wax, stored pollen and larvae) in order to know the amount of the target pesticide potentially available for forager and in-hive bees following the “destiny” of the compounds from the plant to the hive. For systemic compounds or for pesticides sprayed during bloom, residue analysis should be always carried out in the hive matrices. These analyses can be used to know the potential exposure routes for bees and their duration over time.