Allelochemicals in castor (Ricinus communis L.) plants and their impact on pest larval feeding as anti-herbivore defensive

Among the chemical defensive strategies developed by the plant, leaf phenolics generated due to insect herbivory play a major role in controlling the herbivore damage. This study deals with the quantitative and qualitative changes in castor (Ricinus communis L) plant leaf phenolics due to the feeding of its major pests, the castor semilooper [Achaea janata (L.)], tobacco caterpillar [Spodoptera litura (Fabricus)] and the capsule borer [Dichocrosis punctiferalis (Guenee)]. The foliar phenolics extracted from the pest damaged leaves were compared between the pests having different modes of feeding. These experiments revealed the presence of elevated levels of phenolic acid in insect infested plants than uninfested plants. Seven individual phenolic acids were monitored by high performance liquid chromatography (HPLC) in pest damaged and normal healthy castor plant leaves and an increase in vanillic, coumaric, ferulic and syringic acids was noted in the insect infested plants. The impact of increased phenolics on pest feeding behaviour and the growth were analysed through antifeedant assays. A significant difference in the modification of phenolic acids between specialist and generalist leaf feeders was found.