Imidacloprid – Risks to Beneficial Insects

Q: I began treating my shrubs and woody plants with a systemic insecticide last year. Its active ingredient is imidacloprid. Despite its effectiveness, I’m wondering if a systemic insecticide in a plant’s system can be harmful to desirable insects that gather pollen and nectar from that plant.

A: I sought an answer to your question from two leading entomologists and here is what they each responded.

For even more information, see this position paper from Bayer assessing imidacloprid.

From: Dr. Paul Guillebeau,
IPM/Pesticide Coordinator
Department of Entomology
University of Georgia

The only thing that I have heard is some odd sub-lethal effects on bees. The French were calling it mad bee disease. Here is a blurb I put in our newsletter back in 1999. I have not really followed the situation since.

“France has withdrawn the provisional label for Gaucho (imidacloprid) over possible adverse effects on honeybees. The French think that imidacloprid may cause ‘mad bee disease,’ a syndrome in which bees do not behave normally. There are also reports that imidacloprid drenches on tomatoes adversely affect the behavior of bumblebees. Several imidacloprid products are registered in the United States, including Gaucho, Admire, and Provado.” (APIS, 1-99)

There are serious implications if imidacloprid is causing these problems. This pesticide is widely used on a variety of crops, and it has very low toxicity for humans and most non-target species.

From: Dr. Dan Horton
Entomologist
University of Georgia

… I have not done a literature search, however, I have heard similar comments suggesting imidacloprid having a tendency to sometimes cause an increase in mite populations. In peaches, related nicotinoids often increase armored scale. I don’t know if this is from not controlling crawlers, from taking out beneficial insects, or both. I recall reading somewhere that imidacloprid may have negative impacts on bumblebee pollination of glasshouse tomatoes…