Two plant defense theories may predict plant-insect interactions involving inbred plants. The Plant Stress Hypothesis predicts that stressed plants will be more susceptible to generalist herbivores. The Plant Vigor Hypothesis predicts that specialist herbivores prefer and perform better when feeding on the most vigorous plants (low stress plants). Inbreeding (self-pollination) frequently occurs in many plant populations. Inbreeding typically results in broad, detrimental changes in plant morphology and physiology. These phenotypic changes may be analogous to other environmental stresses. We studied the interactions between insect herbivores and their inbred and outbred host plants in an attempt to determine if plant defense theory could accurately predict the effect of inbreeding on plant-insect interactions. Our work with the morning glory, Ipomoea hederaceae var. integriscula (Convolvulaceae), and its generalist and specialist herbivores suggests that plant defense theory may accurately predict the outcome of interactions between inbred plants and their herbivores. Inbred plants were more susceptible to generalist herbivores than specialist herbivores. Conversely, outbred plants were more susceptible to specialist herbivores and not generalist herbivores. In addition, specialist herbivores perform better on outbred plants than inbred plants and they choose to eat outbred plants when given a choice. Thus essential tenets of the Plant Stress/Plant Vigor hypotheses accurately predicted the effects of inbreeding on the outcome of interactions between I. hederaceae and its generalist and specialist herbivores.
Species 1: Lepidoptera Noctuidae Spodoptera exigua (beet armyworm)
Species 2: Coleoptera Chrysomelidae Chariodetlla bicolor (golden tortoise beetle)
Species 3: Coleoptera Chrysomelidae Deloyala guttata (mottled tortoise beetle)
Keywords: plant defense theory, plant stress
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