Herbicidal treatment on R&D Bombus terrestris colonies under lab conditions

The lethal and sublethal effects of insecticide treatment have been widely tested on the Earth buff-tailed bumblebee, Bombus terrestris. However, free-living and open-field pollinators are not exclusively exposed to insecticides but also to herbicides. Topical spraying has been designed to simulate the pollinator's exposure to spray-applied Plant Protection Products (PPPs). In the present study, several herbicides were sprayed on specially designed R&D colonies to investigate the single treatment effect of Maximum Field Recommended Concentrations on these insects' most im-portant toxicological and ecological parameters (colony development, mortality of mother queen, development of gynes). The application of widely used herbicides, such as glyphosate, fluazifop-P-butyl and glufosinate ammonium or herbicide mixes, such as 2,4-D with glyphosate or fluroxypyr with florasulam caused a range of effects to the colonies, from reduced to high mortality on mother queens and adults to the complete death of the colony. In the latter case, a sequential dilution testing scheme is followed to point to a safer field concentration. Considering the severity of this lab study, recommendations for the safe application of the here-tested herbicides are proposed.