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Extension > Garden > Landscape, Nursery and Greenhouse Management > Protecting bees and beneficial insects from systemic insecticides applied in landscapes

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Protecting bees and beneficial insects from systemic insecticides applied in landscapes

Vera Krischik

Why are bees in decline?

Honey bees and native bees, such as bumble bees, pollinate 30% of the plants that produce the vegetables, fruits, and nuts that we consume. More than 100 crops in North America require pollinators. Pollination by bees contributes over $18 billion worth of additional crop yields. In addition, bees pollinate native plants that require seed to sustain future populations. These seeds and fruits from native plants are fed on by many animals, from birds to bears. Both native bees and managed honey bees are in decline due to habitat loss, loss of high quality pollen (protein), loss of nectar plants, pathogens, and pesticide use.

Honey bee colonies in Europe and North America have faced some difficult problems for a long time. Beekeepers have been battling the devastating effects of a parasite of bees called the Varroa mite, which was introduced into Europe in the 1970's and in the US in 1980's and is very difficult to control. Honey bees are also faced with a number of diseases and viruses that compromise their immune systems and health in general. Since WWII, with the increase in monocultures and herbicide use, there has been a serious decrease in flowering plants that bees depend on for food.

Beginning in 2006 a yearly die-off of honey bee colonies occurred throughout the US. The cause of this mortality is still unknown but was coined, colony collapse disorder. Most researchers now agree that honey bee decline is due to multiple, interacting causes, including the effects of bee specific diseases and parasites, lack of floral resources that provide good bee nutrition, and lethal and sub-lethal effects of pesticides. It is known that insecticide use in general can take a toll on honey bees and native bees when the bees are exposed to high enough concentrations.

However, it is unclear how much the neonicotinyl insecticides contribute to honey bee poor health or even mortality. Recent research indicates that bees exposed to relatively low doses of neonicotinyl insecticides (10 ppb) may have suppressed immune systems, which makes them more susceptible to some bee diseases. Research also shows that neonicotinoids can have multiple sublethal effects on bees, including disorientation, effects on learning and a reduction in pollen collection and storage. More research needs to be conducted to determine actual residue levels that bees are exposed to in agricultural and urban environments.

Do systemic, neonicotinyl insecticides contribute to bee decline?

Neonicotinyl, systemic insecticides are the most widely used insecticide in the world, due to their low mammalian toxicity and the ability of the insecticide to move systemically, from soil into the entire plant. Application methods include seed treatments, foliar sprays, soil and trunk drenches, and trunk-injections. There are few systemic insecticides, while there are many systemic herbicides and fungicides.

There are six neonicotinyl active ingredients, imidacloprid, dinotefuran, thiamethoxam, and clothianidin, of which acetamiprid and thiacloprid are the least toxic to bees. There is another systemic insecticide, fipronil. You will find these active ingredients listed on the insecticide label in small print. The neonicotinyl class of insecticides is highly toxic to bees and kills bees at around 180 ppb in flower nectar or pollen. However, sublethal doses of neonicotinyl insecticide starting around 10 ppb, causes bees to lose navigation and foraging skills. The amount of the neonicotinoid compound in the pollen and nectar will depend on the mode of application and the concentration applied to the plant or soil. How long the compound lasts within the plant also depends on application method, concentration applied, and binding capacity of the soil.

The use of neonicotinyl insecticides as trunk injections and soil drenches for ash trees is important to slow the spread of the exotic, invasive Emerald Ash Borer. As bees do not collect ash pollen in quantities, the risk to bee pollinators is low. In contrast, the use of neonicotinyl insecticides on flowering garden plants, shrubs and trees, including linden and basswood trees can kill bees and beneficial insects that utilize the flowers for pollen and nectar. It is wise to avoid using systemic neonicotinyl insecticides on flowering plants that bees visit regularly.

What are bee-friendly flowers?

Retrofit your garden to include many species of flowers that bloom from May to September to provide pollen and nectar to bees and beneficial insects. Avoid treating flowering plants that bees utilize, with any insecticides, especially systemic, neonicotinoids.

There are numerous lists identifying these plants:

  1. CUES: Pollinator Conservation, Plants for bees and other pollinators
  2. CUES: Poster, Save the bees: plant flowers and trees
  3. CUES: Bulletin, Protecting bees and beneficial insects from systemic insecticides applied in landscapes
  4. CUES: Bulletin, Plants for butterfly gardening
  5. CUES: bulletin, Plants that provide pollen and nectar for beneficial insects

Protect bees from insecticides

The conservation of beneficial insects is an essential part of Integrated Pest management (IPM) programs. When scouting plants for pest insects, check for populations of both pest and beneficial insects, such as lady beetles and bees. If beneficial insects are present, wait to spray insecticides to see if the beneficial insects control the pest insects. Do not apply insecticides while plants are in full bloom. If possible avoid beneficial insects by spraying leaves in the evening when bees and lady beetles are not foraging.

Use spot treatments of contact insecticides, not systemic insecticides

Only spot spray the patch of pest insects, never spray flowers or buds. Flowers that open after spraying with contact insecticides do not contain insecticide residue. Use contact insecticides, such as bifenthrin, cyfluthrin, azadirachtin, and spinosad. Toxicity lasts 1-3 weeks. However, flowers that open after systemic insecticides are sprayed can contain the insecticide residue for months.

For discussion with nursery and greenhouse growers: Alternatives to systemic insecticides are contact insecticides, which are available to professional applicators. For the last 10 years the EPA has been registering selective insecticides that conserve beneficial insects and pollinators.

  • pymetrozine, Endeavor, stops mouthparts from feeding/working;
  • flonicamid, Aria, stops mouthparts from feeding/working;
  • pyriproxifen, Distance, diflubenzuron, Adept, Dimilin, or novaluron, Pedestal, IGR, insect growth regulator, stops larval growth;
  • Beauveria bassiana, Botanigard, microbial;
  • s-kinoprene, Enstar II, juvenile hormone mimic;
  • spinosad, Conserve, Entrust, bee friendly when dried;
  • Mites only; Akari, Floramite, Hexygon, Judo, Promite, Sanmite
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