Dietary requirements of individual nectar foragers, and colony-level pollen and nectar consumption: a review to support pesticide exposure assessment for honey bees

Exposure to pesticides is a potential concern for pollinators that may forage on plants containing residues. A key element of estimating dietary risk to pollinators is to determine the nature and amount of food consumed by individuals. Recent efforts have focused on honey bees (Apis mellifera), of which nectar foragers are thought to be at greatest risk of dietary exposure due to their foraging behavior and high energy requirements for the flight-foraging activities. At upper tiers of pesticide risk assessment for honey bees, field studies with whole colonies are carried out to gauge effects of expected exposures; however, without knowing how much nectar and pollen is being consumed by colonies and the potential variability in these parameters, it is difficult to accurately assess risk under other untested exposure scenarios. The objective of this review was to collate available data from the literature regarding (1) the quantity of nectar required by nectar foragers and (2) the quantities of nectar, pollen, and supplements that are consumed by colonies; the purposes being to develop a database that can be used to improve exposure and risk assessments, and to identify data gaps for further research. A number of studies investigating honey bee energetics have been identified that can be used to estimate sugar requirements for foragers under different conditions (e.g., resting, flying). A few more recent studies have been able to quantify the amount of time foragers spend outside the hive. Factors requiring further investigation include levels of energy expenditure while outside the hive, and the sugar content of available nectars, which may also affect foraging behavior. At the colony level, data on food consumption are sparse and primarily anecdotal. Colony size, management, and location seem to be major factors contributing to differences in nectar foraging and honey production. Further research is needed to better quantify and predict colony use and storage of food resources.