- Author: kathy keatley garvey
Originally published on the Bug Squad Blog on January 19, 2015
What's killing the honey bees?
The email arrived in my UC Davis inbox at 9:10 a.m., Thursday, Jan. 8.
An employee from the UC Davis Plumbing Shop wondered what was happening in front of the Robert and Margrit Mondavi Center for the Performing Arts on the UC Davis campus. "There are dead bees everywhere," he wrote, adding that "There were some grounds workers waiting for the UC Davis bus in front of Mondavi, and they commented that they also saw dead bees everywhere in their grounds-keeping areas."
Did the cold spell have something to do with this? But why would honey bees be outside their colony? Honey bees don't fly until the temperature reaches around 55 degrees.
What was happening?
Super sleuth Extension apiculturist (retired) Eric Mussen of the UC Davis Department of Entomology and Nematology, arrived on the scene. He was appropriately dressed in a trenchcoat, a la Sherlock Holmes (Note that Sherlock Holmes, aka physician Sir Arthur Conan Doyle, was a beekeeper, too, according to Wikipedia).
Mussen, who retired last June after 38 years of service, picked up some of the dead bees and noticed that nearly half had small-to-large pollen loads on their legs. Their wings were not tattered. He quickly deduced that the bees had not worn themselves out foraging.
"However, this early in the season, many of the foraging bees are bees that survived since last fall," Mussen said. "Depending upon their overall health, they were working toward the ends of their lives."
Mondavi house manager Kerrilee Knights showed him dead bees on an upper outdoor patio. So the bees were not only dying at ground level but upper levels, Mussen realized.
He noticed some bees flying up over the roof and some live bees "resting" on various parts of the building.
"There's a colony up there somewhere," Mussen said, pointing toward the roof.
Mussen cupped some of the sluggish bees in his hands, and once warmed, off they flew. The other survivors? They were too cold to fly and they would die overnight as the temperature dropped.
Mystery solved. "Elementary, my dear Watson?" No, not really. It's a scene that non-beekeepers rarely see.
"So, it appears that an older population of bees from a colony nesting around the top of the building were foraging near the ends of their lives," Mussen said. "They could not adequately produce enough body heat to keep foraging and they could not adequately produce enough body heat to fly back to their colony and they were falling to the ground, basically exhausted."
"This is normal and no reason for alarm," Mussen said, "except that people usually are not that close to bee colonies to notice the normal demise of substantial numbers of overwintering bees."
So, it wasn't pesticides, pests, diseases, malnutrition or stress.
Old bees and a cold spell...
- Author: James A. Bethke
I often teach that there is a place for pesticides, especially when there are no effective alternatives. For instance, if you leave the aphids alone on your rose plants, they will eventually disappear due to the abundance of all the associated natural enemies like ladybird beetles. Some damage will occur, but the end result will be enjoyable roses in the landscape or in a vase. However, if you are going to show the rose - that first early season rose is the most brilliant - and not protect it, it will not be showable. Similarly, it is a shame if you own a 100-year old beautiful shade tree in your yard and you let a pest destroy it when you could have prevented it.
There is a concern by many that the systemic neonicotinoid insecticides are harming wildlife and the environment, and many folks are not willing to use them or purchase plants that have been treated with them. That is amazingly unfortunate because of all the benefits of this insecticide class, and much of the expressed concerns are scientifically unfounded.
The best example I can give of a fit or a need for insecticide use is presented in the case of the Emerald Ash Borer (EAB). EAB is a beetle as an adult, but the immature form, called a grub, is responsible for girdling ash trees and killing them within three years depending on the size of the tree and the extent of the infestation. EAB has been blamed for killing tens of millions of trees in about 22 states, and it is said, that the destruction of the ash in our forests and urban landscapes could rival the loss of elms due to the Dutch elm disease. That's significant. The benefits of ash trees in the landscape is clear, so the loss of all or nearly all of the landscape ash would be devastating, in my opinion.
There are those, however, that would not protect the trees with neonicotinoid insecticides at any cost. Unfortunately, there are grand examples of communities that refuse to protect their trees with systemic neonicotinoid insecticides, and I recommend that you take a look at the before and after pictures attached and check out the links to more information below. You will see that there is a place for insecticide use in this instance. Some may say that we can replace the landscape trees with alternatives that won't be affected. That's true, but it won't save our forests, and it will leave infected trees in our urban landscapes that will act as a reservoir for the beetle.