Kimberly A. Stoner
Department of Entomology, The Connecticut Agricultural Experiment Station, New Haven, Connecticut

Brian D. Eitzer
Department of Analytical Chemistry,
The Connecticut Agricultural Experiment Station, New Haven, Connecticut

Honeybee in the middle of a black-eyed susan flower


To better understand the levels of pesticides honey bees could be exposed to in the everyday landscape, Dr. Kim Stoner and Brian Eitzer studied the levels of various pesticide residues found in the pollen trapped in honey bees as they returned to the hive. The study took place in apiaries from five locations in Connecticut over two to five years. As honey bees returned to the apiaries (hives) after foraging, they passed through traps that knocked pollen off their bodies. Once pollen was collected, it was tested for chemical residues. As a result of this research, Drs. Stoner and Eitzer proposed using a Pollen Hazard Quotient (PHQ) as well as a standard concentration expressed in parts per billion (ppb) to evaluate pesticide toxicity in bees. PHQ is the concentration in ppb divided by the lethal dose expressed in µg/bee.


Analysis of pollen trapped from honey bees as they return to their hives provides a method of monitoring fluctuations in one route of pesticide exposure over location and time. We collected pollen from apiaries in five locations in Connecticut, including urban, rural, and mixed agricultural sites, for periods from two to five years. Pollen was analyzed for pesticide residues using a standard extraction method widely used for pesticides (QuEChERS) and liquid chromatography/mass spectrometric analysis. Sixty pesticides or metabolites were detected. Because the dose lethal to 50% of adult worker honey bees (LD50) is the only toxicity parameter available for a wide range of pesticides, and among our pesticides there were contact LD50 values ranging from 0.006 to >1000 μg per bee (range 166,000X), and even among insecticides LD50 values ranged from 0.006 to 59.8 μg/bee (10,000X); therefore we propose that in studies of honey bee exposure to pesticides that concentrations be reported as Hazard Quotients as well as in standard concentrations such as parts per billion. We used both contact and oral LD50 values to calculate Pollen Hazard Quotients (PHQ = concentration in ppb ÷ LD50 as μg/bee) when both were available. In this study, pesticide Pollen Hazard Quotients ranged from over 75,000 to 0.01. The pesticides with the greatest Pollen Hazard Quotients at the maximum concentrations found in our study were (in descending order): phosmet, Imidacloprid, indoxacarb, chlorpyrifos, fipronil, thiamethoxam, azinphos-methyl, and fenthion, all with at least one Pollen Hazard Quotient (using contact or oral LD50) over 500. At the maximum rate of pollen consumption by nurse bees, a Pollen Hazard Quotient of 500 would be approximately equivalent to consuming 0.5% of the LD50 per day. We also present an example of a Nectar Hazard Quotient and the percentage of LD50 per day at the maximum nectar consumption rate.

Download paper by Stoner and Eitzer