In some cases, the indirect toxicity tests can be preferred to topical tests because they better simulate the field conditions of the exposure and provide fast and applicable data (see 188.8.131.52.1.). In the indirect or residual toxicity tests, bees enter in contact with the test substance by walking on contaminated substrate in a hording cage (Williams et al., 2013). The “OPPTS 850.3030 Honey bee toxicity of residues on foliage” is the unique official guideline designed to develop data on residual toxicity to honey bees for spray products but no official methods are available to test contaminated dust in laboratory. In fact, individual compounds can show different levels of toxicity depending on formulation (spray vs. dust for example) but, specific tests should be adopted to estimate the toxicity of powder products when pesticides are applied as seed treatment.
Several bee mortalities in Europe and USA have been linked with contaminated dust dispersed during maize sowing operations (Alix et al., 2009; Bortolotti et al., 2009; Pistorius et al., 2009; Krupke et al., 2012). Pesticides can be dispersed by air during sowing operations when pesticide-dressed seeds are used and contaminated dusts can subsequently deposit on soil and vegetation, posing an exposure risk to foraging bees (Greatti et al., 2003, 2006). In this section, a method to test the impact of contaminated dusts on honey bees is proposed.