The genus Acerocephala and observations of the life history of Acerocephala hanuuanamu sp. nov. (Hymenoptera, Cerocephalidae) and its bark beetle host on the island of O‘ahu, Hawai‘i

Abstract

The behavior of Acerocephala hanuuanamu sp. nov. found parasitizing Cryphalus brasiliensis under the surface of wood in Ficus microcarpa trees on the island of O‘ahu in Hawai‘i is deduced from observations in naturally occuring branches, and from direct observation using specially designed “phloem sandwich” observation chambers which consist of tree bark peeled through the phloem layer from freshly cut branches and sandwiched between a sheet of aluminum and a sheet of plexiglass. Cryphalus brasiliensis beetles, found living in large numbers in the phloem tissues in F. microcarpa trees, were collected and placed into these chambers. They tunneled into the wood and reproduced, producing an active colony of all life stages. Acerocephala hanuuanamu wasps were then placed into the system and their behavior observed. Typical behavior, aspects of which were recorded in video and still images, was as follows. A female A. hanuuanamu enters the tunnels of the bark beetles. She digs through the debris in the tunnels in a search for larvae and pupae. Cryphalus brasiliensis prepupae construct a hard pupal chamber around themselves before they pupate, and upon encountering a larva in the tunnels or the exterior of a pupal chamber with a pupa inside, she adeptly turns around in the tunnel to sting it, either inserting her ovipositor directly into the larva or by laboriously pushing it through the hard shell of the pupal chamber. When finished stinging, she withdraws her ovipositor slowly and carefully, often extracting tissue from the beetle immature as a sheath around her ovipositor. This structure remains projecting from the larva or pupa, and then the wasp turns around and host feeds through this structure, in the case of a pupa at a substantial distance through the wall of the pupal chamber. Oviposition occurs on larval stages and pupal stages. The egg hatches and the larva develops as an ectoparasitoid on the beetle. When finished feeding, it detaches and pupates in the tunnel. Mating behavior is also described. In addition to C. brasiliensis in F. microcarpa, A. hanuuanamu was also observed attacking Cryphalus mangiferae in mango (Mangifera indica) branches. Acerocephala ihulena sp. nov. was also found on O‘ahu parasitizing Eidophelus pacificus in hau (Hibiscus tiliaceus) branches, and is described. The genus Acerocephala is revised given the perspective resulting from these two new species and aspects of functional morphology observed in the behavioral studies, Acerocephala indica comb. nov. is transferred to the genus, and a key to the genus is provided.