Usually, the insecticides were quick-acting nerve toxins designed to kill any insect, including beneficial insects like bees, on contact. Although they are targeted at insects, the broad-spectrum insecticides can harm any creature that lives in or passes through areas in which they have been sprayed. This includes earthworms, birds, squirrels, dogs, cats and even people. Most manufacturers of insecticides used in the yard recommend waiting three days before walking barefoot on the sprayed areas and to keep pets and children away for at least that long.
People living as much as a quarter mile away from the insecticide application can be affected by evaporated insecticide and aerosols drifting in the air. In some individuals, this can result in severe reactions like headaches and numbness in the limbs. In others, it can cause less noticeable effects that might never be connected with the true cause of the reaction: toxic insecticides being applied somewhere in the neighborhood.
Neem's natural properties pose no danger of toxic reactions. The seeds and leaves of the neem tree are the source of a new class of "soft" pesticides. The term "soft" pesticide is used because no other word quite fits this remarkable product. The main mode of action is as an anti-feedant. Insect pests usually refuse to eat any plant covered with neem and do so until they starve to death. Other effects are as a repellent and a reducer of an insect's ability to reproduce.
Elimination of the insect pest occurs not by quick poisoning, but by starvation and drastic reductions in offspring. Birds and beneficial insects, which are not affected by neem, then feed on the remaining weakened pests and the small number of remaining offspring. The result is an almost-immediate halt to plant damage -- without poisoning the environment.
Neem is non-toxic to animals or people. Areas sprayed with neem are not poisonous areas to be avoided for days as are those sprayed with the typical synthetic insecticides. Neem is also a natural, biodegradable product. Only insects that eat plants are affected by neem, leaving honeybees and other beneficial insects essentially unharmed. In fact, in those areas sprayed with neem, the average size and number of earthworms is greater than in unsprayed areas.
The most active insecticidal compound found in neem is azadirachtin which acts as an anti-feedant. Azadirachtin causes insects to refuse to eat plants sprayed with neem. Insects will land and crawl on the plants but will refuse to eat as long as the azadirachtin is on the plant. In early tests of neem extracts, the desert locust, which is known for its voracious appetite, refused to eat any plants sprayed with neem and eventually starved to death surrounded by its favorite food.
As important as azadirachtin is, neem's true effectiveness comes from the interaction of all of the compounds which affect different aspects of an insect's life. Other compounds act as insect repellents, cause insects to lay sterile egg cases, prevent molting, and others simply enhance the effects of other compounds. The number and complexity of the compounds found in neem that affect insects make resistance to neem highly unlikely. This is extremely important as insects are rapidly developing resistance to the major synthetic insecticides. More and more insects are even developing resistance even to natural bacterial controls like Bacillus thuringensis (Bt).
Synthetic pesticides are less expensive in the short run, but factoring in their total impact dramatically increases their true long-term cost.
Neem has been found to be beneficial to bees. Bees are coming under assault on several fronts. There are mites and diseases that cause bees to produce less pollen and honey and to become sick and die. Neem treated bees showed reduced levels of Nosema and chalkbrood even over bees treated with the most current medicines and miticides. The neem treated bees produced three times as much pollen and twice the amount of honey as the non-treated bees.