Leaf buds, a factor in host selection by Battus philenor butterflies

.1 Field and laboratory experiments identified a character intrinsic to Aristolochia reticulata Nutt. host plants, the terminal leaf bud, that is involved in host‐selection behaviour by female pipevine swallowtail butterflies ( Battus philenor L.) searching for oviposition sites. 2 In the field, the frequency with which females landed on non‐host buds declined seasonally as the proportion of host foliage that consisted of buds decreased. Female butterflies did not land on non‐host species in proportion to their abundance; rather, females landed on those non‐host species whose buds resembled those of A.reticulata.3 A.reticulata plants whose terminal leaf bud was concealed by plastic tape were less susceptible to oviposition in the field than were control plants. 4 Female butterflies released in a large, outdoor enclosure were conditioned to search for leaf buds only when exposed to a host species bearing a prominent terminal leaf bud. 5 The significance of conditioning of leaf‐bud searching behaviour is discussed with respect to discrimination between hosts and non‐hosts, between host species, and among plants within a host species.