Host plant trichomes and the advantage of being big: progeny size variation of the pipevine swallowtail

1. Plants possess numerous traits that confer resistance against insect herbivores, and herbivores, in turn, can evolve traits to ameliorate the effectiveness of these traits. The pipevine swallowtail, Battus philenor, is an extreme specialist on plants in the genus Aristolochia. The only host plant available to the California population of B. philenor is A. californica. Aristolochia californica is distinct from most other B. philenor host plants in that it is pubescent. 2. The progeny of B. philenor are larger in California compared with populations examined in Texas. Size differences persist throughout larval development. 3. Regardless of maternal host plant, population differences in progeny size persist, and crosses between California (large progeny) and Texas (small progeny) B. philenor populations resulted in offspring producing intermediate sized progeny, indicating a heritable component to progeny size variation. 4. California neonate caterpillars more easily overcame the trichomes of A. californica compared with Texas neonates. When trichomes were removed from A. californica, time to feeding establishment was reduced for caterpillars from both populations. Texas caterpillars established feeding sites on A. californica with trichomes removed, in the same time required to establish feeding on their non‐pubescent host plant, A. erecta. 5. This study shows that plant trichomes might impose selection pressure on progeny size.