Kimberly A. Stoner
Department of Entomology, The Connecticut Agricultural Experiment Station, New Haven, Connecticut

Brian D. Eitzer
Department of Analytical Chemistry,
The Connecticut Agricultural Experiment Station, New Haven, Connecticut


Pot filled with soil and little seedling emerging.Neonicotinoids are a group of systemic insecticides that have come under recent scrutiny because of the threats they pose to bees. Dr. Kim Stoner and Dr. Brian Eitzer studied the levels of two specific neonicotinoids in squash plants after being applied directly to the soil. They used imidacloprid—which accounts for 26% of the global insecticide market—and thiamethoxam. They found residue levels in the entire plant, nectar, and pollen of the squash. However, while the results found residue levels below the EPA concern threshold, the levels found in the squash were being investigated for sub-lethal effects on honey bees and bumble bees.

Imidacloprid and Thiamethoxam are the largest selling insecticides in the world. Dr. Stoner and Dr. Eitzer studied the movement of these systemic insecticides throughout squash plants to determine the concentration of the insecticide in the fully developed plant, nectar, and pollen. The squash was treated two ways: by spraying the insecticide into the soil before seeding and applied through drip irrigation in a single treatment after transplant. The study found that the entire plant had a higher concentration of insecticides than just the flowers, nectar, or pollen. The results found concentrations of 10 ±3 for Imidacloprid and 11±6 ppb of Thiamethoxam in nectar and 14±8 ppb of Imidacloprid and 12±9 ppb Thiamethoxam in pollen. The concentration found in the squash fell into the range of what is being investigated in the range of what is believed to be sub-lethal for bees.


There has been recent interest in the threat to bees posed by the use of systemic insecticides. One concern is that systemic insecticides may translocate from the soil into pollen and nectar of plants, where they would be ingested by pollinators. This paper reports on the movement of two such systemic neonicotinoid insecticides, imidacloprid and thiamethoxam, into the pollen and nectar of flowers of squash (Cucurbita pepo cultivars ‘‘Multipik,’’ ‘‘Sunray’’ and ‘‘Bush Delicata’’) when applied to soil by two methods: (1) sprayed into soil before seeding, or (2) applied through drip irrigation in a single treatment after transplant.

Download Movement of Soil-Applied Imidacloprid paper