Larval morphology of the hangingfly Bicaubittacus longiprocessus (Huang and Hua, 2005) (Mecoptera: Bittacidae) and its taxonomic significance

Fossils in Myanmar amber demonstrate the diversity of anti-predator strategies of Cretaceous holometabolan insect larvae

Holometabolan larvae are a major part of the animal biomass and an important food source for many animals. Many larvae evolved anti-predator strategies and some of these can even be recognized in fossils. A Lagerstätte known for well-preserved holometabolan larvae is the approximately 100-million-year-old Kachin amber from Myanmar. Fossils can not only allow to identify structural defensive specializations, but also lifestyle and even behavioral aspects. We review here the different defensive strategies employed by various holometabolan larvae found in Kachin amber, also reporting new cases of a leaf-mining hymenopteran caterpillar and a hangingfly caterpillar with extensive spines. This overview demonstrates that already 100 million years ago many modern strategies had already evolved in multiple lineages, but also reveals some cases of now extinct strategies. The repetitive independent evolution of similar strategies in distantly related lineages indicates that several strategies evolved convergently as a result of similar selective pressures.

Mouthpart structure of the adult Bicaubittacus appendiculatus () (Mecoptera: Bittacidae)

The structure and functional morphology of the mouthparts were investigated in adult hangingfly Bicaubittacus appendiculatus (Esben-Petersen, 1927) by scanning electron microscopy and histological serial sections. The mandibulate mouthparts consist of a labrum-epipharynx, paired mandibles and maxillae, and unpaired labium and hypopharynx. The labrum is elongated and tapered toward the apex. The epipharynx is furnished with numerous sensilla. The mandibles are sword-shaped, with an outer sharp tooth curved mesad and an inner blunt corner. The basal region of each mandible processes a conical projection. The maxillae are well-developed, each consisting of a sclerotized cardo, an elongated stipes, which bears an inner lacinia, an outer galea, and laterally a five-segmented maxillary palp. The labium is formed by a postmentum, a prementum and a pair of two-segmented labial palps. The hypopharynx is concave inward on the anterior side, with numerous microtrichia on the posterior surface. Seven types of sensilla were found on the mouthparts: sensilla basiconica on the epipharynx, and maxillary and labial palps; sensilla chaetica on the epipharynx; sensilla palmata, sensilla placoidea and sensilla trichodea on the epipharynx and maxillary palp; sensilla campaniformia and hair plates on the basal joints of palps. The sensillar function and the feeding mechanism of mouthparts in bittacids are briefly discussed.