Myrmecophily in Hesperiidae. The case of Vettius tertianus in ant gardens

The larvae of the hesperiid butterfly Vettius tertianus develop by eating t he leaves of Aechmea mertensii, a bromeliad epiphyte restricted to ant gard ens. The relationships between ants and V. tertianus larvae highlight the p referential association of the caterpillars with Pachycondyla goeldii (Pone rinae), an ant-garden initiator. The oviposition strategy of V. tertianus m ay thus imply the identification of the inhabiting ant species and not only the identification of the host plant. The caterpillars neither provide sec retions to the ants, nor possess defensive devices (i.e. hairs or appendice s) against ants. Their activity rhythm does not isolate them from foraging workers of P. goeldii and their shelters are also attainable by the ants. M oreover, as the cuticular lipid profiles of V. tertianus larvae are clearly different from those of the ants and also from the leaf-surface of A. mert ensii, acceptance is not due to mimicry between larvae and plants or ants. However, the caterpillars deposit, on the leaf they eat, silk containing a mixture of substances very similar to those found on their own cuticle. No interaction with ants was recorded during observations, even though the ant gardens were patrolled by numerous P. goeldii individuals during their act ivity period. But when confronted with the caterpillar, none of the tested ant species reacted aggressively. These results suggest the existence of co mpounds, other than cuticular lipids, responsible for the absence of aggres siveness in the ants. The case of V. tertianus is relatively new as myrmeco phily with in Hesperiidae has been described only once. Moreover, it prefer entially involves a member of the Ponerinae, a subfamily in which interacti ons with other arthropods are exceptional. (C) 2000 Academie des sciences/E ditions scientifiques et medicales Elsevier SAS.