Which pesticide formulations are least hazardous to honey bees?

Different formulations of the same insecticide often vary considerably in their toxicity to bees. Granular insecticides generally are not hazardous to honey bees. Dust formulations (seldom used today on commercial field crops) are typically more hazardous than emulsifiable concentrates because they adhere to the bee’s body hairs and are carried back to the beehive. Wettable powder and flowable formulations essentially dry to a dust-like form which foragers can carry to the hives. Likewise, microencapsulated insecticides can be collected by foragers along with pollen and carried back to the beehive. When honey bees are exposed to insecticides that kill foraging bees, honey production is reduced but colonies recover as young bees emerge. Exposure to dust, wettable powder, flowable, and microencapsulated formulations of insecticides can cause severe losses of both foraging bees and hive bees. In the worst cases, toxins may remain active in the hive for several months and prevent colonies from recovering from the injury. – Marion Ellis, University of Nebraska