Horticultural Oil . . .

How Horticultural Oil Work

These oils (except neem oil) kill insects by suffocating them. Oils also kill insect eggs by penetrating the shells and interfering with metabolic and respiratory processes. In addition, oils disrupt feeding by insects such as flea beetles, white-flies, and aphids without necessarily killing them.

The fact that oils kill insects by smothering is a key virtue. Many other pesticides kill them by interfering with biochemical processes that are similar to those in other animals, including people. What kills a tiny insect can make us sick, too.

Also, oils have few residual effects and so their impact on beneficial or benign insects is minimal.

From DoItYourelf.com