Structure and Distribution of Sensilla on the Mouthpart Palps in Caddisflies of the Family Hydropsychidae (Trichoptera)

A comparative morphological study of the structure and distribution of sensilla on the maxillary and labial palps in caddisflies of the family Hydropsychidae was performed. Morphology of palpal sensilla was studied by scanning electron microscopy in 17 species from 12 genera. The palps of the studied species have four types of sensilla: long trichoid, chaetoid, campaniform, and petaloid; at the same time, no basiconic and pseudoplacoid sensilla were found on the palps. All the studied species lack apical sensory complexes at the tips of both pairs of palps, where only long chaetoid sensilla are present. Petaloid sensilla form sensory fields on the 4th (in Arctopsychinae) or on the 3rd and 4th segments (in Diplectroninae, Hydropsychinae, Macronematinae) of the maxillary palps, but sensilla of this type are never present on the labial palps. The sensory fields include from 5–10 sensilla in Hydropsychinae to 40 sensilla in Arctopsychinae.