Hi,

Depending upon the insecticide, the plant and the method of application (injection vs spray vs seed coating, etc.) the answers vary.

Here are a number of links that discuss various insecticides, methods of application and vulnerable insects:
http://www.extension.umn.edu/garden/plant-nursery-health/protecting-bees-beneficial-insects-systemic...

http://www.extension.umn.edu/garden/plant-nursery-health/toxicity-to-pollinators/

Most harm occurs when a systemic is used on the same plant for consecutive seasons because the insecticide builds up in the soil.

Although neonics have been implicated in the decline of pollinators, it's important to realize that many other factors come into play as well. In the meantime, try to purchase "Bee Friendly" plants from the nurseries next year, and encourage the
vendors to avoid growers who use neonicotinoids.

For a much longer, fairly scientific examination of this issue, here is another link that is very helpful:
http://www.xerces.org/wp-content/uploads/2012/03/Are-Neonicotinoids-Killing-Bees_Xerces-Society1.pdf.

(Thanks to Mary C for her research on this question.)