18.104.22.168. Returning foragers as a tool to measure the pesticide confrontation and the transport into the bee colony
After the application of a pesticide in blooming cultivations or orchards, forager bees might be contaminated during their flight (Schur and Wallner, 1998). Also systemic pesticides may reach nectar and pollen of seed treated plants or after spray applications before the blooming stage (Wallner, 2009). The bee body itself and the collected goods contain residues of the applied ingredients.
Residue analysis with honey showed that this bee product is inadequate to measure the realistic level with which single bees are confronted. During honey preparation, honey bees have a remarkable influence on the residue level in honey. Reduction factors up to 1000 times have been shown between the nectar contamination and prepared honey. Based on the lypophilic character of the pesticide, colonies are more or less successful at reducing the contamination level. As a general rule, harvested honey is less contaminated than harvested nectar (Wallner, 2009). Therefore honey cannot be used to access the pesticide levels that bees have to handle on their flights. A much better tool, even to demonstrate that there was a contact to sprayed fields, is the analysis of returning foragers and their loads (Reetz et al., 2012). This can be done in field experiments as well as in tent tests with reasonable plot sizes.
the analysis of returning foragers at the hive entrance, it is also possible to
collect bees directly from plants or flowers. In this case, a 12 Volt vacuum,
which can be run with a car battery, is useful (Wallner, 1997). Residue
analysis is performed on the basis of single bees (pollen loads or honey
stomach content) or pooled groups of one sampling date.