ABSTRACT ELISA techniques were used to detect imidacloprid in guttation fluid of young cantaloupe plants in Arizona. Imidacloprid was detected at up to 4.1 micro g/ml (ppm) in a coincidental guttation collection 3 d after a top label rate soil application and at 37 micro g/ml one d after a separate top label rate soil application study. These imidacloprid titers exceed reported median oral toxicities for several insect species by factors of 10 or more. Pesticides in guttation fluid are a relatively unexplored route of exposure for both pest and beneficial insects, and could represent an important risk for both of these groups in guttation-prone environments.
"The reviewed data of imidacloprid oral toxicities suggest that imidacloprid concentrations below 20 ppm (micro g/ml) are toxic to a broad range of insects. For the most sensitive species, the guttation concentrations recorded here exceed median lethal concentrations by a factor of 10 or more."
"Our results affirm recent reports (Girolami et al. 2009, Thompson 2010, Tapparo et al. 2011) that viewed guttation fluid containing imidacloprid as a risk factor to honey bees and other sensitive benefcial insects. The occurrence of guttation in arid environments such as Arizona is probably rare, but the fact that guttation fluid was observed and collected unexpectedly in August, and again in October as part of a planned study, suggests a need for future attention."
Eric J. Hoffmann and Steven J. Castle, 2012. Imidacloprid in Melon Guttation Fluid: A Potential Mode of Exposure for Pest and Beneficial Organisms, Journal of Economic Entomology, 105(1):67-71.