Honeybee deaths may be caused by a mix of different pesticides, not just one in particular.

A honeybee pollinates an apple blossom. Photo: Shutterstock

Bees are dying in record numbers—in fact, seven species of the Hawaiian yellow-faced bees have recently been placed on the endangered species list—but scientists are still having a hard time figuring out why. There have been numerous studies that have tried to address the question of what is causing colony collapse disorder, but so far researchers have not been able to isolate any single cause.

Most research points to one kind of pesticide or another, but there have been no conclusive findings relating to exactly which pesticide might be causing the deaths.

A recent study has found another potential culprit. Researchers from the University of Maryland have found that the problem may not be any specific pesticide or fungicide, but that it could be the combination of them. The team followed 91 honeybee colonies and found that the ones that suffered the most had the largest number of toxins within the colony. They found that although one pesticide might not hurt a colony by itself, when mixed with other pesticides, the combined toxins seemed to cause the largest die-offs.

Dennis vanEngelsdorp, an assistant professor of entomology at the University of Maryland and senior author of the study, said, “Our results fly in the face of one of the basic tenets of toxicology: that the dose makes the poison. We found that the number of different compounds was highly predictive of colony death.”

The researchers looked at colonies as unified organisms instead focusing their attention on individual bees, which helped them realize that they were brining in multiple poisons which, put together, often resulted in the death of queens. Without a queen the colony will die. Sometimes a colony can create a new queen to replace one that was lost and recover, but not without significant losses.

The researchers’ next goal is to figure out ways to reduce the number of chemicals used in agriculture to as few as possible which won’t harm bees but can still allow farmers to best grow their crops.