Bioinsecticidal effect of the flavonoids pinocembrin and quercetin against Spodoptera frugiperda

Flavonoids function in many aspects of plant-insect interactions, but the responses of insects to these compounds vary greatly. In this study, we determined the effects of two widely distributed flavonoids, pinocembrin and quercetin, on the feeding behavior, survival, and development of the fall armyworm Spodoptera frugiperda J.E. (Smith) (Lepidoptera: Noctuidae). In a choice test, S. frugiperda larvae strongly rejected leaves treated with pinocembrin at concentrations of 10, 50, or 100 mu g/cm(2). Larvae fed normally on leaves treated with quercetin at 10 and 50 mu g/cm(2), but showed 57 % deterrence when fed on leaves treated with 100 mu g/cm(2) quercetin. At concentrations of 0.01-1 A mu g/cm(2), pinocembrin and quercetin functioned as phagostimulants for S. frugiperda. In a multiple-choice experiment, S. frugiperda larvae preferred to consume untreated leaves or those treated with 0.1 A mu g/cm(2) pinocembrin, but rejected leaves treated with 5-50 A mu g/cm(2) pinocembrin. In a no-choice feeding experiment, larvae fed on leaves treated with 5 and 50 mu g/cm(2) pinocembrin consumed less than those fed on leaves treated with 0.1 and 1 mu g/cm(2) pinocembrin or untreated leaves. Pinocembrin at 1-50 mu g/cm(2) negatively affected larval weight and survival, thus showing a toxic effect. In contrast, leaf consumption and larval weight were not significantly affected by quercetin at 0.1, 1, 5, and 50 mu g/cm(2), and mortality rates only slightly increased. Because of its dual activity, pinocembrin could be used for insect control in a stimulo-deterrent diversionary strategy: the same compound could promote both stimulate (low doses) and deter insect activity (high doses).