Antifeedant Effects of Citrus Limonoids Differing in A-Ring Structure on Colorado Potato Beetle (Coleoptera: Chrysomelidae) Larvae

The antifeedant effects of three citrus limonoids (limonin, obacunone, and nomilin) which differ only in the structure of the A-ring were compared in feeding assays with fourth-instar Colorado potato beetles, Leptinotarsa decemljneata (Say). In contrast to studies with other insects, the results of choice assays showed no differences among the three limonoids in their ability to deter feeding. No-choice assays also indicated no differences among the limonoids and, along with incidental observations, suggested that all three Iimonoids acted as toxins. The changes in the A-ring represented by obacunone and nomilin may be important in enhancing deterrency against some insect species but have no effect in increasing the toxicity of limonoids against Colorado potato beetle larvae