Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2008
Publication Date: 5/17/2008
Citation: Johnson, E.T., Berhow, M.A., Dowd, P.F. 2008. Colored and white sectors from star-patterned Petunia flowers display differential resistance to corn earworm and cabbage looper larvae. Journal of Chemical Ecology. 34:757-765. DOI: 10.1007/s10886-008-9444-0 Interpretive Summary: Insect damage to crops causes billions of dollars of losses each year. In addition, the insect damage also causes contamination with mold toxins, which also causes losses. New sources of insect resistance, preferably identified from plant sources, could help minimize these losses. Petunia flowers with a star pattern of alternating colored and white sectors were used for studies on insect resistance. The experiments found that cabbage-feeding and corn ear-eating caterpillars ate more of the white sectors than colored sectors. The most resistant petunia sectors were colored purple to blue. Growth of the cabbage-feeding and corn-earworm caterpillars was significantly inhibited by partially purified mixtures of the pigments from one of the purple-sectored petunia lines. These studies indicate that some petunia pigments are moderately effective insect resistance molecules. Genetic modification of valuable crop plants to produce similar pigments in specific tissues may result in lower crop damage.
Technical Abstract: Anthocyanins are likely a visual aid for attracting pollinators. However, there is also the possibility that anthocyanins are present in some flowers as defensive molecules protecting them from excess light, pathogens or herbivores. In this study, resistance due to anthocyanins from commercial petunia flowers (Petunia hybrida) was examined for insecticide/antifeedant activity against corn earworm (CEW, Helicoverpa zea) and cabbage looper (CL, Trichoplusia ni). The petunia flowers studied contained a star pattern, with colored and white sectors. CEW larvae ate significantly less colored sectors than white sectors in most cases. All CEW larvae feeding on blue sectors weighed significantly less after two days than larvae feeding on white sectors, which was negatively correlated with total anthocyanin levels. CL larvae ate less of blue sectors than white sectors, and blue sectors from one petunia cultivar caused significantly higher CL mortality than white sectors. Partially purified anthocyanin mixtures isolated from petunia flowers, when added to insect diet discs at approximately natural concentrations, significantly inhibited both CEW and CL larva development. These studies demonstrate that the colored sectors of these petunia cultivars slow the development of these lepidopteran larvae and indicate that anthocyanins play some part in flower defense in petunia.