|MadSci Network: Biochemistry|
There are a variety of ways in which insecticide sprays kill. Many depend upon which insect you are wanting to eliminate. Many fly sprays work in a similar fashion.
These insecticides generally attack and disable the nervous system insects. Some must be ingested, others are so potent that they work "on contact" as do the sprays. The most common contact spray ingredient is Pyrethrin. This ingrediant is very fast acting and imobilizes flying insects almost instantaneously. However, pyrethrin does not last long in well lighted environments and thus degrades.
Much more information can be found on the links provided below. The best link to describe Pyrethrin in general is:
http://npic.orst.edu/factsheets/pyrethrins.pdf (28kb PDF download): Pyrethrin factsheet (though this file is password protected, if you click "DONE" in the password window, you will be able to read it).
For more genral information about insecticides please see the following links:
Try the links in the MadSci Library for more information on Biochemistry.