Two phenolic compounds occurring in nature were useful in the control of some pests. Salicylaldehyde is a substance produced by some plants and some animals. A novel pest control agent is based on salicylaldehyde. It is active against caterpillars (larvae of butterflies and moths) as well as earthworms and molluscs. In combination with garlic extract it enhances the activity of such extract. An agent for the control of insects in agriculture comprises vanillin. The vanillin powder is solubilised in water for spraying onto insects infesting crops.