A quick check at Wikipedia will give you the following information about Neem Oil:

Neem oil is a vegetable oil pressed from the fruits and seeds of the neem (Azadirachta indica), an evergreen tree which is endemic to the Indian subcontinent and has been introduced to many other areas in the tropics. It is perhaps the most important of the commercially available products of neem for organic farming and medicines.

“Neem oil is not used for cooking purposes. In India and Pakistan, it is used for preparing cosmetics (soap, hair products, body hygiene creams, hand creams) and in Ayurvedic, Unani and folklore traditional medicine, in the treatment of a wide range of afflictions. The most frequently reported indications in ancient Ayurvedic writings are skin diseases, inflammations and fevers, and more recently rheumatic disorders, insect repellent and insecticide effects.

“Formulations made of neem oil also find wide usage as a bio-pesticide for organic farming, as it repels a wide variety of pests including the mealy bug, beet armyworm, aphids, the cabbage worm, thrips, whiteflies, mites, fungus gnats, beetles, moth larvae, mushroom flies, leafminers, caterpillars, locust, nematodes and the Japanese beetleNeem oil is not known to be harmful to mammals, birds, earthworms or some beneficial insects such as butterflies, honeybees and ladybugs. It can be used as a household pesticide for ant, bedbug, cockroach, housefly, sand fly, snail, termite and mosquitoes both as repellent and larvicide (Puri 1999). Neem oil also controls black spot, powdery mildew, anthracnose and rust (fungus).”  (Emphasis added)

What is important to the organic gardener is that it is generally a safe and effective insecticide that does not appear to harm beneficial insects…or your pets!  Gardeners should be aware that Neem oil does not work like chemical pesticides and the process for it to work is much slower.  That means, you have to be patient when looking for results.

Whereas chemical insecticides give almost immediate results and you can visually see the insects dying in front of you, Neem oil works on an insects neurological and reproductive systems.  It causes them to get confused to the point of forgetting they can fly, forgetting to eat, and more importantly, renders them unable to reproduce.  It is this life-cycle destroying effect that slowly eliminates your bug problems.

Neem oil can be an effective and affordable addition to your organic pest control efforts.

Prices accurate as of 11/19/2012