Amy Moorhouse, 2012

Minnesota State University Moorhead

Nipped in the Bud: New Groundcherry Moth Performs Better as a Frugivore than a Budworm

All organisms have a specific strategy for eating, and while most have one strategy, a few have multiple. Life history feeding polymorphism is when organisms of the same species utilize multiple feeding strategies at one life stage, particularly at the larval stage. Larval feeding polymorphism may signify either 1) intraspecific competition over a preferred resource, such that the polymorphism only occurs when the preferred resource limits population growth or 2) variation in the success of one strategy over another under different contexts, such that a poor strategy under some circumstances may be a good strategy during others. The groundcherry moth (Symmetrischema sp.) exhibits a feeding polymorphism while utilizing its host plant, Physalis spp. The larvae either feed on a single fruit or a single floral bud, but it is not known what guides the choice or governs the outcome of each strategy. To explore this, I looked for differences in body size, development time, predation, and parasitism across feeding strategies. I found that frugivores have larger pupal weights, and depending on the conditions can have a higher survival rate than budworms, but that larvae under both strategies take the same time to develop. With each generation, frugivores, which enter larger floral buds, are the first to be produced, indicating that it is the preferred strategy. I also found that frugivores were able to induce parthenocarpic fruit, thus ensuring fruit formation even in the absence of pollinators. In order to support large moth populations when larger buds are insufficient to support frugivores, larvae must use the secondary strategy of bud herbivory. Thus, intraspecific competition appears to be driving the use of the less preferred resource. Consequently, this reduces the potential for future frugivory, as buds used for the secondary strategy are no longer able to reach the size needed to support frugivores, thus shifting the entire system into the less preferred strategy.

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