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  • From: Douglas Woodard <>
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  • Subject: [NAFEX] Bees and pesticides: intake mode
  • Date: Fri, 30 Apr 2010 19:47:15 -0400

Pesticide Dew - Exposure route for bees

dew dropHumans aren't the only ones whose drinking water has been
contaminated by pesticides: in Europe, a new study

finds that the insects already on the frontlines

in the battle
against toxic pesticides are consuming lethal doses of neonicitinoid
pesticides in the droplets of dew [SIC] they drink. Plants emit guttation
droplets -- a source of morning dew -- as part of their respiration
process. These droplets of water are a favorite source of moisture and
nutrients for bees to drink from after leaving the hive in the morning.
Germans scientists have found that seeds treated with neonicitinoid
pesticides such as imidacloprid (Gaucho) and clothianidin (Poncho) show
contaminated guttation droplets for as long as two months after
germination. The study, which looked at corn, barley and canola plants,
showed levels were highest during the ten days after germination -- as
high as 100 parts per million (ppm). Two weeks after germination, levels
were closer to 10 ppm. Levels of imidacloprid in the pollen of plants
treated with commercial levels of the pesticide averaged around 3.4 ppm
- 1,000 times lower than the levels found in the guttation droplets.
Imidacloprid has been shown to affect bees with as little as 0.1
nanogram. A range of serious effects has been documented in the 1-20
nanogram per bee level. This means that a bee drinking a small fraction
of a guttation droplet with 100 ppm of imidacloprid would be consuming a
potentially fatal dose. The study's authors say that in light of their
findings, strong and rapid action is needed to protect bee populations.

*shareMORE** *Film trailer:* *Vanishing of the Bees


Warning: "Guttation is not to be confused with dew" -



Guttation is probably a route for other insects including parasitic and predatory insects (e.g. parasitic/parasitoid wasps) to ingest pesticides
which enter plant sap, whether they are primarily systemic in action or not. I surmise that they are especially dangerous when the night air is dry (which often happens on warm summer nights in southern Ontario and Quebec) and the soil is moist (which also often happens here), so guttation droplets would be present without the alternative of dew.

Doug Woodard
St. Catharines, Ontario

  • [NAFEX] Bees and pesticides: intake mode, Douglas Woodard, 04/30/2010

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