A sad and avoidable incident. Avoidable in several ways especially when spraying for waterborne mosquitos rather than for insects that bother the same plants bees pollinate.
1-Avoid spraying near bee hives. Hives tend to be easy to spot. Anyone who can't identify a modern bee hive has no business being tasked to commercially spray insecticides.
2-Spray in the evening. Bees are headed home and less likely to be affected. By the time they leave the hive the next morning, the spray has settled onto areas of little interest to honeybees.
3-Give the beekeepers a little notice. It is entirely possible and usually quite practical to seal up the hives for a day to reduce exposure to insecticide if the spraying has to be done during the day and has to be done in areas near hives. You still need to avoid directly spraying the hive itself, but can spray the area around it without too much problem for the bees if they are confined to the hive for the day. On especially hot days confinement can cause problems. But on moderate days, entirely possible and safe to confine the bees inside the hive for 24 hours.
As for colony size, somewhere between 20k and 50k during peak spring summer months; almost all of which are female worker bees, plus 1 queen, and a few hundred male drones. Over the winter the number drops as low 10k (for a hive that survives and comes out of winter healthy; it can drop to zero for hives that don't survive), with no or almost no drones present.
Charles
