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