Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2011
Publication Date: 5/1/2011
Citation: Dowd, P.F., Berhow, M.A., Johnson, E.T. 2011. Differential activity of multiple saponins against omnivorous insects with varying feeding preferences. Journal of Chemical Ecology. 37(5):443-449. Interpretive Summary: Insects that damage corn ears cause billions of dollars of losses each year due to yield reductions and contamination of ears with mold toxins. Several different compounds in the group called saponins, which also can have human health benefits, were tested against two major corn ear pests, the corn earworm and fall armyworm. Some of the compounds were active against both insect species, and some came from soybeans, switchgrass, and some tropical plants. Certain groups need to be present on the molecules for activity against the two insect species. Enhancing saponin levels through breeding or introduction of appropriate biosynthetic genes should reduce damage by these ear feeding insects, thereby increasing yields, reducing the levels of mold toxins, and making the corn safer for humans and animals and more marketable for exporters.
Technical Abstract: A variety of saponin glycosides and aglycones from seven different plant families (Aquifoliaceae, Asparagaceae, Caryophyllaceae, Dioscoreaceae, Leguminosae, Rosaceae, Sapindaceae) were tested against the corn earworm, Helicoverpa zea, and the fall armyworm, Spodoptera frugiperda. The corn earworm feeds readily on both monocots and dicots, while the fall armyworm is primarily a grass feeder. Most of the saponins were similarly effective or ineffective against both insect species, with the glucosides being the primary active form (compared to aglycones). Thus, in contrast to many plant secondary metabolites effective against either of these two species where the aglycone is more effective; in the case of the saponins, the opposite is true. This appears to be contradictory strategy of plant defenses that requires further consideration. The activity of protodioscin against insects is reported for the first time and may be important in insect defense by the bioenergy crop switchgrass.