Guttation is a natural process seen in many vascular plants whereby drops of xylem sap exude from leaf tips or margins. Honey bees are known to drink this water, especially in the early spring before large numbers of nectar-containing flowers are available to foragers.
A problem with this type of water collection occurs in agricultural areas where plants are treated with systemic insecticides. Bees collecting guttation drops can be poisoned by the pesticides flowing through the xylem. Worse, sublethal doses of pesticide can be carried back to the hive and fed to the developing larvae by way of the nurses. Researchers are currently trying to determine the type and frequency of damage this may cause to honey bee colonies.
Tests were performed in Italy to see if the guttation drops of corn treated with seed dressings of neonicotinoid pesticides contained enough pesticide to damage bees. The researchers used corn seed treated with three different systemic neonicotinoids (imidacloprid, thiamethoxam, and clothianidan) and one moderately systemic pesticide (fipronil). The seeds were purchased from the manufacturer with the pesticide already applied and ready for commercial distribution.
Guttation drops were collected from seedling emergence through the first three weeks of growth. For each individual seedling, the drops were collected and held at 2? C. After 2-3 days half the liquid was sent away for analysis and half was used for the bee experiments.
Bees held in captivity were chosen at random and caged with the drops. The bees were monitored constantly and timed from the beginning of drinking until they began to show symptoms. The two symptoms monitored were arching of the abdomen and paralysis of the wings. Previous research has shown that wing paralysis is not reversible, so once that happened it was assumed those bees would die.
The results showed that there was easily enough of all three of the systemic pesticides in the drops to cause wing paralysis and death. The moderately systemic fipronil was not found in the guttation drops.
However, not all the drops containing the insecticides contained a lethal dose. In a way, this is even worse because doses low enough that they don’t kill the forager may be carried home and fed to the developing young–a result that could have serious effects on the survival of the colony. Doses of poison that don’t kill an adult bee may have developmental effects on the young larvae.
If you would like to read the whole article, the information is below.
Girolami, V., L. Mazzon, A. Squartini, N. Mori, M. Marzaro, A. Di Bernardo, M. Greatti, C. Giorio, A. Tapparo. 2009. 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.