International audienceAssessment of the toxicity of individual pesticides to honeybees is routinely assessed. However, few data have been generated for realistic mixtures of neonicotinoid insecticides and fungicides particularly with regard to exposure levels used. Assessment of the effects of exposure of bees to predicted residues following sprayed applications of ergosterol biosynthesis inhibitor fungicides on the contact and oral toxicity of a range of neonicotinoid insecticides (thiamethoxam, clothianidin, imidacloprid and thiacloprid) showed only low levels of synergism (<3-fold maximum). Further studies showed that the scale of increase in toxicity was fungicide dose dependent with greater synergy of oral toxicity of thiamethoxam following contact dosing with propiconazole. This underlines the need for the use of realistic exposure levels and routes in studies

The present study was designed to assess homing behavior of bees foraging on winter oilseed rape grown from seed treated with thiamethoxam (as Cruiser OSR), with 1 field drilled with thiamethoxam-treated seed and 2 control fields drilled with fungicide-only-treated seed. Twelve honeybee colonies were used per treatment group, 4 each located at the field edge (on-field site), at approximately 500 m and 1000 m from the field. A total of nearly 300 newly emerged bees per colony were fitted (tagged) with Mic3 radio frequency identification (RFID) transponders and introduced into each of the 36 study hives. The RFID readers fitted to the entrances of the test colonies were used to monitor the activity of the tagged bees for the duration of the 5-wk flowering period of the crop. These activity data were analyzed to assess any impact on flight activity of bees foraging on the treated compared with untreated crops. Honeybees were seen to be actively foraging within all 3 treatment groups during the exposure period. The data for the more than 3000 RFID-tagged bees and more than 90 000 foraging flights monitored throughout the exposure phase for the study follow the same trends across the treatment and controls and at each of the 3 apiary distances, indicating that there were no effects from foraging on the treated crop. Under the experimental conditions, there was no effect of foraging on thiamethoxam-treated oilseed rape on honeybee flight activity or on their ability to return to the hive.

This study provides evidence of a direct antifeedant effect of imidacloprid and clothianidin in individual bumblebees but highlights that this may be a compound-specific effect.

B. terrestris colonies placed adjacent to a field of flowering oilseed rape grown from thiamethoxam-treated seed developed at a comparable rate with colonies placed adjacent to oilseed rape grown from untreated seed. © 2015 Society of Chemical Industry.

Consideration of the solubility of the toxic reference and test items when designing studies is important. The use of higher rates of acetone in the present study more closely represents the true exposure of larvae to pesticides that are not highly soluble in diet. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.