Herbivore Offense

Herbivore offense describes traits that allow herbivores to increase their feeding and other uses of host plants when these uses benefit the herbivores. We argue that ecological interactions and coevolution between plants and herbivores cannot be understood without an offense-defense framework. Thus far, plant defense theory and data have far outpaced knowledge of herbivore offense. Offensive tactics include feeding and oviposition choices, enzymatic metabolism of plant compounds, sequestration, morphological adaptations, symbionts, induction of plant galls, and induced plant susceptibility, trenching, and gregarious feeding. We propose that offensive tactics can be categorized usefully depending upon when they are effective and whether they are plastic or fixed traits. The advantages of offensive traits have not been adequately described in terms of herbivore fitness. Similarly, a more complete understanding of the costs and limitations of offensive traits will help put the herbivore back in plant-herbivore interactions and coevolution.