Pesticidal compositions based on nontoxic, naturally unstable insecticides (pyrethrum, synthetic pyrethroids and mixtures thereof) include a liquid alkyl aryl silicone polymer which stabilizes the insecticide to provide an extended effective killing life. The compositions additionally include a synergist to provide an immediate killing action and an antioxidant to protect the insecticide against destruction by oxygen. Ultraviolet protectants and insect repellents may also be included. Applications include control of insect pests to animals and plants and general purpose insect control. Exemplary formulations are given for compositions to be applied as sprays, dips, powdered or dusts, foggers and shampoos.