D3141: How do phenotypic differences among Silphium integrifolium ecotypes affect pest insect performance?

Silphium integrifolium (“silphium”), a perennial plant native to prairies of North America, is being domesticated as an oilseeds crop in central Kansas, with its use as forage and for pollinator services also being explored. Understanding silphium’s existing pest defense capabilities is key to breeding a hardy perennial crop whose ingrained defenses are part of integrated pest management. Silphium from different ecotypes display a range of leaf, stem, vein, and flower traits. We hypothesize that some of these traits may provide physical defense against herbivory. To test this hypothesis, we conducted a bioassay using fall army worms (Spotoptera frugiperda). We tested silphium genotypes grown from wild-collected seed from an east-west rain gradient: central Kansas, eastern Kansas, and central Illionois. We placed leaves from 93 of these genotypes on agar plates with the caterpillars and compared weight gain of the pest across ecotypes and across plant traits. Plant traits associated with low caterpillar weight gain would imply higher defense for the corresponding genotypes possessing those traits. Statistical analyses of pest performance and implications for plant defenses will be discussed.