BASAL HATCHING BY MACULINEA BUTTERFLY EGGS - A CONSEQUENCE OF ADVANCED MYRMECOPHILY

Larvae of Maculinea alcon and M. rebeli are unique among Holarctic Lycaenidae in hatching through the base of the eggshell and emerging on the opposite side of the leaf to the egg. This occurs because the exposed upper surfaces of their eggs have exceptionally thick shells. Other species of Maculinea have normal or unusually thin‐shelled eggs. It is suggested that both types of Maculinea eggshell have evolved to reduce mortalities from parasitoids and predators. Maculinea alcon and M. rebeli are forced to lay in exposed places due to the structure of their foodplants, and protect their eggs with thick shells. The other three species hide their eggs deep within the inflorescences of their foodplants; M. nausithous and M. teleius require thin flexible shells to achieve this. These adaptations are necessary because Maculinea eggs often occur at much higher densities on their initial foodplants and are hence more vulnerable—than is the case with other Lycaenidae. This is a consequence of myrmecophily. Maculinea population size is regulated more by the status of the ant host than by that of the initial foodplant. Large Maculinea populations, and high densities of eggs, occur on the many sites where the ant is abundant but the foodplant is scarce. Maculinea alcon and M. rebeli eggs occur at the highest densities, and need the greatest protection, due to the advanced form of myrmecophily found in these species. Whereas M. anon, M. teleius and M. nausithous larvae are predators of ant brood, M. alcon and M. rebeli feed mainly at a lower trophic level on ant regurgitations. This leads to roughly seven times more M. alcon and M. rebeli adults emerging per ant nest, and to a similar increase in egg densities per foodplant. Copyright © 1991, Wiley Blackwell. All rights reserved