August 22nd is National Honey Bee Day so we thought we'd repost one of our previous articles that discussed ways gardeners can help protect honey bees.
Most people have heard about the decline in honey bees (Figures 1 and 2) during the last several years and want to help. Gardeners and landscapers who want to help protect honey bees can do so by learning more about the factors that cause bee decline and by practicing Integrated Pest Management or IPM.
Better Nutrition, Fewer Pesticides
The actual cause of honey bee decline is still uncertain. What is known is a number of factors are probably involved. Honey bees are their most robust and able to best contend with stresses when well fed. In addition to water, honey bees require nectar sources for carbohydrates and a varied mix of pollens to provide proteins, lipids, vitamins, minerals, sterols, antioxidants, and other nutrients. Drought, flooding, and conversion of former foraging grounds into large agricultural monocultures, highways, airports, developments, and so forth have led to honey bee malnutrition in many locations.
In the last 20 years beekeepers have been encountering a series of previously exotic pests that invade the hive and kill bees, such as the varroa mite; new honey bee diseases, including Nosema ceranae; and many viruses.
Pesticides can also be involved in bee decline, especially when applied to plants when they are in bloom and bees are foraging. Many insecticides are highly toxic to bees including virtually all organophosphates, carbamates, and pyrethroids. If not killed in the field, foraging bees can collect residue-contaminated pollens and bring them back to the hive for immediate consumption or long-term storage. There are serious concerns over the chronic, sublethal effects of these residues on the physiology of immature and adult bees.
A newer class of insecticides, the neonicotinoids, which include imidacloprid, clothianidin, and dinotefuran, also pose hazards for honey bees. These products are systemic materials that move through the plant and are included in the nectar and pollen of flowers when they bloom. Although the neonicotinoid residues may not kill bees immediately, they may have sublethal effects, such as suppressing immune and detoxification systems, causing bees to be more sensitive to other stresses.
There are several ways you can help protect bees. When designing or replanting a landscape, consider honey bees and other pollinators in your plan. Use plants honey bees prefer, and ensure several bee-friendly plants will be blooming throughout the year (Figure 3). See the UC Davis Haagen-Daz Honey Bee Haven web page or the UC Urban Bee Gardens page for lists of California native plants bees visit. Also, if bees are still visiting certain flowers, delay removing spent flowers until bee visits taper off, even if the results aren't as aesthetically pleasing.
In addition, avoid applying highly toxic insecticides, especially when plants are in bloom. With neonicotinoids, avoid applying them before plants bloom, because these materials tend to be stable compounds that can remain in the soil and in plants for months. Even when plants aren't in bloom, use nonchemical management methods or pesticides with little or low toxicity to bees such as soaps, oils, or Bacillus thuringiensis whenever possible, as pesticides may leave toxic residues, or there may be flowering weeds or other blooms nearby.
For information about the relative toxicity of pesticides to bees, consult the publication How to Reduce Bee Poisoning from Pesticides. Toxicity of many landscape and garden pesticides to bees is also listed in the UC IPM landscape and garden pesticide active ingredient database.
This article was originally published in the June 2013 issue of the UC IPM Retail Nursery & Garden Center IPM News.