Coevolution in Insect Herbivores and Conifers

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Abstract
The use of anti-herbivore toxins in a long-lived perennial has coevolutionary consequences. Individual trees will benefit by diverging from the defensive pattern of their neighbor, and the array of toxins should be diverse. For the pine-scale system, differentiated insect populations will develop on individual trees, reducing the fitness of the insect offspring on hosts of differing defense phenotypes. Intraspecific defensive variation forces the coevolved herbivore into an evolutionary dichotomy. Breeding and cloning programs for rapid-growth conifers can narrow variation in the pine gene pool. Reduction of defensive variation will destabilize coevolutionary equilibrium, increasing vulnerability of trees to insect damage. Maintaining defensive heterogeneity in plants should be a major objective in agricultural genetics.
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