A new group of plant-derived naphthoquinone pesticides

A series of compounds with structures based on insecticidal/acaricidal naphthoquinones isolated from Calceolaria andina has been synthesised. A feature of the series is the lack of resistance shown by strains resistant to established classes of pesticides. The importance for activity of the tetra-substituted carbon atom in the side-chain, as observed in the natural products, has been investigated. In analogues with acyclic side-chains the position of the tetra-substituted carbon for optimum activity was dependent on the length of the sidechain. With cyclic side-chains, activity was dependent on the size of the ring, the number and position of the substituents therein. Activity of the compounds examined was particularly high against Bemisia tabaci and Tetranychus urticae in direct-contact tests, but was much lower than expected in leaf-dip tests. A partial improvement based on formulation has been demonstrated.