Host plants and immatures as mate-searching cues in Heliconius butterflies

The study of interactions between phytophagous insects and their host plants extends beyond understanding how insects deal with plant chemical defences. Sexual behaviour of these herbivores is integrated in several ways with host plants, as the latter influence timing and location of reproduction, and can provide clues for finding mates. Nevertheless, while numerous studies link butterfly evolution to host plant adaptations, the influence of plants on butterfly sexual behaviour has been little studied. We conducted experiments to determine the role of host plant cues in mate-searching behaviour of Heliconius charithonia butterflies. This species exhibits precopulatory mate guarding behaviour, wherein males find and perch on pupae, then copulate with eclosing females (‘pupal mating’). We found that males (1) visited plants damaged by feeding larvae more often than they visited undamaged plants and (2) displayed searching behaviour around the plant and in front of larvae, suggesting that odours signal the location of potential partners (pupae). Although males were attracted to common plant odours released after tissue damage, plants damaged by heterospecific butterfly larvae were less attractive, indicating that species recognition can occur at early life stages. Overall, our results suggest that host plants influence mate-searching behaviour of Heliconius. This might also be true for other species of butterflies with more conventional mating strategies, potentially contributing to the diversification of this group of phytophagous insects.