Probabilistic assessment of nectar requirements for nectar-foraging honey bees

Abstract

Recent concerns regarding potential effects of pesticides on pollinators have prompted regulatory agencies to estimate dietary ingestion rates for honey bees (Apis mellifera). The task is difficult because of the complex caste and food storage systems in honey bee colonies. Considerable data on the nutrition and energetics of honey bees have recently been collated. These data were used to parameterize a probabilistic model estimating nectar requirements of nectar foragers. Median estimates were more than 6× lower than the recommended median value from the North American government agencies, of 292 mg nectar/bee/day. The distribution of estimates had much greater variability than those of the agencies. The differences are due primarily to the disparate assumptions regarding how much time nectar foragers spend flying and foraging. Risk assessors considering honey bee dietary exposure should take account of current and emerging data providing insight into nectar forager dietary requirements, foraging activity, and feeding behavior.

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

“…Synthesis of the data was not straightforward due to the diverse study objectives, inconsistency in experimental units, and statistics reported among the reviewed studies. In a subsequent modeling exercise carried out to estimate nectar forager nectar requirements (Rodney and Kramer 2019), data were integrated by calculating weighted averages and pooled variances across studies where practicable for pertinent model parameters. See Table I (Comparison of Agencies and revised model input assumptions for honey bee nectar forager nectar requirement estimates) and Table II (Summary of input assumptions for RP model for honey bee nectar forager nectar requirement estimates) in (Rodney and Kramer 2019).…”

“…Under natural foraging conditions, mean numbers of trips per day by workers range from 1 to 13.5, with a maximum reported value of 24 trips for a single bee-day. See Table S3 (Summary of data collected on number of trips taken per day by honey bee workers) in Online Resource 3, and also Table I (Comparison of Agencies and revised model input assumptions for honey bee nectar forager nectar requirement estimates) in Rodney and Kramer (2019). Again though, the purposes of the trips were generally not reported but are presumed to be primarily foraging trips.…”

“…Overall average time outside the hive per flying day falls between 0.95 and 3.06 h. See Table S4 (Summary of RFID results reporting on mean time spent outside the hive by honey bee workers) in Online Resource 3, and also Table II (Summary of input assumptions for RP model for honey bee nectar forager nectar requirement estimates) in Rodney and Kramer (2019). In addition, Thom et al (2000) reported that 70% of nectar foragers in their study foraged for less than 4.5 h (despite over 15 h of daylight).…”

“…Generally, the lowest demand for sugar occurs in foragers at ectothermic rest, and the highest demand occurs when bees are hovering or flying. See Table S7 (Estimates of sugar metabolism by resting or motionless honey bee workers), Table S8 (Estimated sugar metabolism of tethered flying honey bee workers) and Table S9 (Estimates of sugar metabolism by honey bee workers performing a variety of activities (untethered)) in Online Resource 3, and also Table I (Comparison of Agencies and revised model input assumptions for honey bee nectar forager nectar requirement estimates) in Rodney and Kramer (2019). However, there are a number of factors other than observed activity level that impact metabolism in individual workers.…”

“…The data compiled for individual nectar foragers was subsequently used to model nectar requirements and compare estimates with those of the Agencies (Rodney and Kramer 2019).…”