Pyrethrum is a nerve poison and paralyzes insects on contact. Nicotine, another botanical insecticide, is best not use it is very highly toxic to mammals. Organic sprays and dusts include insecticidal soap and diatomaceous earth. Both are effective against soft-bodied insects such as aphids, spider mites, and some caterpillars. Insecticidal soaps penetrate insect membranes, causing paralysis and starvation.
Diatomaceous earth is a dust composed of the fossilized skeletons of microscopic sea organisms.
The individual particles are sharp and cut insect bodies, causing them to dehydrate and die. It is applied as a dust, or in a water solution. Homemade sprays of ground up garlic and hot peppers can also effectively repel some insect pests. Cultural and mechanical practices involve handpicking insect pests when they are few in number and crushing them underfoot, keeping the yard and garden free of decaying refuse, rotating the position of crops each year, and maintaining healthy plants with fertile soil. Bt works in a natural, environmentally friendly manner.