Pesticide Exposure of Insect Pollinators

 

An accurate picture of potential risk involves a reliable estimation of both hazard and exposure. Since the hazard of a compound is an inherent quality, mitigating risk most often involves mitigating the potential exposure to a pesticide.

 

Depending upon the product formulation and the application method, the route(s) of exposure, or the degree of exposure can differ. For example, both foliar applied and soil applied pesticides may lead to exposure via the pollen and nectar; however residues levels in the pollen and nectar between these two application methods will differ. Other exposure routes that may be relevant within the treatment site include:

  • residues in pollen and nectar carried back to the hive from foraging bees
    uptake of residues by insect pollinators from drinking water (e.g., guttation fluid, other water sources containing residues such as damp soil or puddles)
  • residues found in the soil, or 
  • residues found on/in the understory forage (e.g. flowering weeds)

 

Off-site exposure routes may also occur due to spray drift at the time of ground or aerial spray applications, or dust drift associated with planting pesticide treated seed.

 

Knowledge of the pesticide product and how it is intended to be used helps inform both the risk assessor and the risk manager of the potential exposure routes that need to be examined and thereby leads to a more accurate risk assessment and more informed risk mitigation. Because of the importance of exposure in risk analysis, pesticide risk assessments often contain details on potential exposure routes. Exposure diagrams which visually depict the potential exposure routes through which an insect pollinator or colony may be exposed can be used to clarify potential exposure routes.

 

While there is general agreement among regulatory authorities on the potential routes of exposure, differences can exist between regulatory authorities regarding which routes of exposure are accounted for in a risk assessment. Below is a generic example of a pesticide exposure diagram for honey bees (applicable also to bumblebees).

 

This figure presents the major routes of exposure of foraging bees to pesticides.

Image reproduced from EFSA 2012 (EFSA Panel on Plant Protection Products and their Residues (PPR); 'Scientific Opinion on the science behind the development of a risk assessment of Plant Protection Products on bees (Apis mellifera, Bombus spp. and solitary bees)'. EFSA Journal 2012; 10(5) 2668. [275 pp.] doi:10.2903/j.efsa.2012.2668.)

 

The table below summarises potential pesticide exposure routes, and their relative importance, for both Apis mellifera and non-Apis bees.

 

Table reproduced from Fischer, D. and Moriarty, T. (2011): "Pesticide risk assessment for pollinators - Summary of a Society of Environmental Toxicology and Chemistry (SETAC Pellston Workshop, Pensacola FL (USA): Society of Environmental Toxicology and Chemistry (SETAC)).

Table reproduced from Fischer, D and Moriarty, T. (2011). Pesticide risk assessment for pollinators: Summary of a Society of Environmental Toxicology and Chemistry (SETAC Pellston Workshop.  Pensacola FL (USA): Society of Environmental Toxicology and Chemistry (SETAC).