Elongated mouthparts of nectar-feeding Meloidae (Coleoptera)

Abstract

Coleoptera of at least three taxa in the Nemognathini (Meloidae) possess mouthparts that are specialized for nectar feeding from flowers with a deep corolla. Parts of the maxillae are modified to form an elongate proboscis-like organ. In Leptopalpus species, the four-segmented maxillary palps form the proboscis, whereas in Nemognatha and Gnathium species, the elongated galeae enable nectar feeding. With the use of scanning electron microscopy and micro computerized tomography, the present study clearly demonstrated that neither of the two kinds of proboscides possesses a median food canal. The filiform galeae of Nemognatha and Gnathium species are densely covered with long bristles; in Gnathium species the tip bears conspicuous sensilla. Nectar uptake is probably accomplished by capillarity along the bristles of the proboscis and is enhanced by the cibarial and pharyngeal musculature. The investigation of Leptopalpus species revealed a muscular valve-like structure in the head that probably closes the pharynx and could be part of a sucking pump in conjunction with the compressor and dilator muscles of the cibarium and prepharynx. In addition to nectar feeding by means of the maxillae, these Coleoptera feed on pollen using their mandibles. Morphological and anatomical results yield new insights into the functional aspects of proboscides in nectar-feeding Meloidae that probably evolved at least two times convergently, that is, by elongation of the maxillary palps or the galeae.