Yes, insecticides do cause bees to die
A common insecticide really does contribute to the death of bees, according to a large-scale field study. This helps set to rest some of the controversy over the use of the chemicals.
The type of insecticide in question, called neonicotinoids, is often used to coat crops. In a study published today in the journal Science, researchers grew rapeseed in 33 sites across Germany, the United Kingdom, and Hungary. They coated the crop with neonicotinoids, introduced various bee species to the area, and monitored the health of the colonies compared to control groups. (These chemicals were made by the companies Bayer CropScience and Syngenta, which helped fund the study.) The bees who lived near the plants treated with neonicotinoids had more trouble surviving the winter.