Adding a snippet to the Plant Whisperer post, Steven Ley at the University of Cambridge has worked for 22 years to make a natural compound that stops predatory insects from feeding but will not harm bees or ladybugs, animals or people.
Azadirachtin is a highly active substance that inhibits the development of the larvae of a broad spectrum of destructive insects. Found on the neem tree in 1968, learning how to make the complicated molecule started in 1985. [story at Science blog]
Using plant extracts and powdered plant parts as insecticides started near the time of Roman Empire. When chemical insecticides appeared in the 1940s, problems also appeared such as environmental contamination, residues in food and increasing resistance. There is no doubt biological insecticides are a top choice for safe pest control, but only a few of the more than 250,000 plant species have been adequately evaluated.