Inbreeding frequently occurs in many plant populations and typically results in broad, detrimental changes in plant morphology and physiology. How these changes affect the herbivores that encounter inbred plants may provide insight as to why mixed mating systems are maintained in plant populations. Previous studies suggest that inbreeding ins analogous to plant stress. We placed larvae of two tortoise beetles (specialist leaf feeders), beet armyworms (generalist leaf feeders) and cotton aphids (generalist phloem feeders) on inbred and outbred plants in the greenhouse. The plant stress hypothesis predicts that generalist herbivores will perform better on inbred (stressed) plants; whereas plant vigor hypothesis predicts that specialist herbivores will perform better on outbred (healthy) plants. Growth rate and weight at pupation were recorded for beetles and armyworms as an indication of response to host plant. Increase in population density was recorded as the indication for aphids. We found that both specialist tortoise beetles and generalist armyworms performed better when reared on outbred plants, but that aphid density increased significantly faster on inbred plants. Our work with the morning glory, Ipomoea hederacea var. integriuscula (Convolvulaceae), and its generalist and specialist herbivores suggests that feeding strategy determine the response of these herbivores to inbreeding.
Species 1: Coleoptera Chrysomelidae Charidotella bicolor (golden tortoise beetle)
Species 2: Lepidoptera Noctuidae Spodoptera exigua (beet armyworm)
Species 3: Homoptera Aphididae Aphis gossypii (cotton aphid, melon aphid)
Keywords: plant defense, morning glory
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