Metro Atlanta Beekeepers Association

Guttation – New Pesticide Concern?

By Eric Mussen, Ph.D.  Entomology Extension, University of California Davis

What is guttation? It is a mechanism by which a plant can secrete water, taken up by the roots, which is excess to the plants immediate needs for growth and biochemical processing. Guttation is not pure water, but is mixed with materials we refer to as plant sap, often containing sugar. Guttation normally occurs over night, but it can be a daytime phenomenon.

The secreted droplets form along the edges and tips of leaves through pores called hydathodes. To the casual observer, this might look like dew. However, dew forms by condensation, all over the surface of the leaf.

Guttation droplets can be collected and analyzed for presence of systemic agricultural chemicals, such as herbicides, fungicides, and/or insecticides.

Recent colony collapse disorder (CCD) problems have led to various studies as to possible causes. In this case V. Girolami and eight other researchers in Italy teamed up to determine the amount of neonicotinoid that would be found in young corn plant guttation secretions from plants germinated from seeds coated with thiamethoxam, clothianidin, and imidacloprid, and from plants germinated from untreated seeds (the controls).

Seeds were planted in the field and in greenhouse pots. Guttation droplets were collected over three weeks and divided into two groups: one for chemical analysis and one for feeding to bees.

Bees in cages were fed known quantities of the insecticides in 15% honey syrup to determine the effects on the bees. Intoxication was observed at three successive levels. Least affected bees showed a “jerky inward arching of the abdomen.” Second was paralysis of the thoracic muscles, inhibiting flight. Finally, the bees died.

Imidacloprid moved into the field and lab droplets in the highest concentration, followed by clothianidin, then thiamethoxam. Interestingly, toxic effects of consuming the guttation liquid developed in the exact opposite order, thiamethoxam paralyzing the bees quickest and imidacloprid slowest. All residues were lethal.

Since newer varieties of corn can be planted early in the season, the corn plants and guttation droplets are available before flowers come into bloom. Water-foraging bees may collect that liquid (not analyzed for sugar content in this study). The authors concluded: “Regardless, the presence of a source of water carrying in solution neonicotinoid concentrations up to the levels shown in the current study, and persisting for weeks on more than a million hectares in northern Italy, is a threatening scenario that does not comply with an ecologically acceptable situation.”

For details see: “Translocation of Neonicotinoid Insecticides from Coated Seeds to Seedling Guttation Drops: A Novel Way of Intoxication for Bees,” Journal of Economic Entomology 102(5): 1808-1815, 2009.

In a separate study on rapeseed treated with a chlorpyriphos/cypermethrin mix in the Czech Republic it was determined that the secreted guttation droplets did not contain enough of the chemicals to damage the bees acutely, or enough to be detected by instrumental residue analysis. However, guttation fluid put into the sugar syrup reduced syrup consumption significantly.