How leaf domatia and induced plant resistance affect herbivores, natural enemies and plant performance

Predators and plant resistance may act together to control herbivorous arth ropod populations or antagonistically, which would reduce the control of pe st populations. In a field experiment we enhanced predation by adding simul ated leaf domatia to plants. Leaf domatia are small structures that often h arbor predaceous arthropods that are potentially beneficial to the plant. W e also manipulated host plant duality by inducing resistance with controlle d. early season exposure of seedlings to spider mite herbivory. Our manipulations had profound consequences for the natural community of ar thropods that inhabited the plants. Leaf domatia had a direct positive effe ct on abundances of two species of bugs and one species of thrips, all of w hich are largely predators of herbivores. On leaves with domatia, each of t he predators was found inside the domatia two to three times more often tha n outside the domatia. Eggs of predaceous bugs inside leaf domatia were pro tected from parasitism compared to eggs outside the domatia. The positive e ffects of leaf domatia on predator abundances were associated with reduced populations of herbivorous spider mites, aphids, and whiteflies. Plants wit h experimental leaf domatia showed significantly enhanced reproductive perf ormance. Induced resistance also affected the community of arthropods. Of the abunda nt predators, all of which also fed on the plant, only minute pirate bugs w ere negatively affected by induced resistance. Populations of herbivorous s pider mites and whiteflies were directly and negatively affected by inducti on. In contrast, aphid populations were higher on plants with induced resis tance compared to uninduced plants. Effects of induced resistance and domat ia were additive for each of the predators and for aphids. However, spider mite and whitefly populations were not suppressed Further by employing both induced resistance and domatia compared to each strategy alone. Our manipu lations suggest that plant defense strategies can have positive effects on some species and negative effects on others. Negative effects of "resistanc e trails" on predators and positive effects on some herbivores may reduce t he benefits of constitutive expression of resistance traits and may favor i nducible defense strategies. Multiple plant strategies such as inducible re sistance and morphological traits that aid in the recruitment of predators of herbivores may act together to maximize plant defenses, although they ma y also be redundant and not act additively.