- 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.
- Author: james bethke
- Editor: ryan krason
This new online course was created primarily for pest control advisors and other licensed pesticide applicators and highlights how pesticide resistance develops among pests. It also describes the mechanisms of resistance in pathogens, insects, and weeds and ways to manage resistance within the different diciplines. It is divided into three narrated presentation followed by a final test for each section. This course has been approved for 2 continuing education units in the "other" category from the Department of Pesticide Regulation.
This course is based on a series of workshops held in Davis, Fresno and at the Kearney Agricultural Research and Extension Center during the spring of 2014 presented by Dr. Doug Gubler (Dept. of Plant Pathology, UC Davis), Dr. Larry Godfrey (Dept. of Entomology and Nematology, UC Davis), Dr. Beth Grafton-Cardwell (Lindcove Research and Extension Center and UC Riverside), and Dr. Kassim Al-Khatibi (UC Statewide IPM Program).
- Author: James Bethke
- Contributor: Ryan Krason
Insecticides play an important role in pest management efforts in California, but it's very important to keep sprays on-target. Improper targeting or poorly maintained equipment can cause spray drift, which can result in unnecessary exposure to people, wildlife and the environment. With that in mind, your application technique and equipment maintenance are keys to reducing the movement of insecticides.
Spray drift occurs when spray droplets are carried from the application site and deposited on non-target sites. Spray drift can also occur from vapor drift (evaporation of insecticide from a plant surface) and particle drift (spray carrier droplets evaporate, leaving concentrated insecticide droplets). Spray drift is influenced mainly by droplet size; the larger the droplet, the less likely it will be carried off-site. Since small droplets are lighter and remain airborne longer than larger ones, they travel greater distances from the treatment site. A high spray height or wide nozzle tip angle will also increase drift distance. Several environmental and spray conditions affecting spray drift potential are shown below:
Factor |
More Drift |
Less Drift |
Nozzle Type |
Fine droplets |
Coarse droplets |
Nozzle Orifice Size |
Smaller |
Larger |
Nozzle Height |
Higher |
Lower |
Spray Pressure |
Higher |
Lower |
Wind Speed |
Higher |
Lower |
Air Temperature |
Higher |
Lower |
Relative Humidity |
Lower |
Higher |
Air Stability |
Vertically Stable |
Vertical Movement |
Insecticide Volatility |
Volatile |
Non-volatile |
To increase pest control success and reduce the likelihood of spray drift, consider the following application factors before
spraying:
- Label Instructions: Carefully read and follow directions before applying
- Environmental Conditions: Take weather conditions into consideration before spraying (i.e. wind, rain, fog, temperature, time of day, etc.).
- Buffer Zones: Leave adequate space between treatment site and non-targets.
- The Sprayer: Maintain equipment and calibrate for efficient use of insecticides.
- Nozzle Selection: Using a spray nozzle that emits large droplets is less prone to drift Spray Pressure: Keep spray pressure as low as possible according to the label instructions.
- Spray Volume: Check nozzle tip wear frequently and change when the flow rate differs by 10% from that of a new nozzle.
- Boom & Nozzle Height: Operate nozzles at their lowest recommended height.
- Travel Speed: Use a travel speed of 3-5 mph. Above 6 mph can create a wind-sheer effect on spray droplets.
- Spray Additives: Spray drift retardants can reduce drift by up to 95%.
*Adapted from Kurt Hembree and Stephen Vasquez-Farm Advisory, UCCE, Fresno County
- Author: James A. Bethke
- Author: Mary Louise Flint
[From the July 2014 issue of the UC IPM Retail Nursery & Garden Center News]