Both biological control and host plant resistance are effective and safe means to protect crops against pests. Historically, these two mechanisms were thought to be independent, with one having no effect on the other. We now know that biological control agents may be harmed by the same plant traits that confer resistance to pests. Such effects present a difficulty in predicting the evolution of plant defenses: should evolution favor strong defenses that act directly on pests, or reduced defenses to favor the pests' natural enemies? This question will be answered by comparing the benefits for plant reproduction of a resistance trait that acts directly on pests with its indirect effects on the pests' natural enemies. Datura wrightii, an abundant, native species of jimsonweed, is ideal for such a comparison. The trait that helps plants resist pests, glandular hairs, is controlled by a single dominant gene. Glandular plants are less suitable for pests but glandular hairs also inhibit the natural enemies of these pests. I will quantify the direct and indirect effects of glandular hairs on seed production of D. wrightii in field experiments, determine the seasonal variation in densities of herbivores and natural enemies on glandular and non-glandular D. wrightii plants in natural populations, and determine the influence of glandular hairs on the foraging behavior of natural enemies in the laboratory. This research is among the first to disentangle the direct benefits of pest resistance from its indirect effects on natural enemies and has broad applicability to better integrate host plant resistance with biological control in the management of pests of potato, tomato, and other crops. A postdoctoral research associate, a graduate student, and several undergraduate students from NSF's underrepresented ethnic groups will be mentored and trained under this research project.
