Do grazing caddisfly larvae of Melampophylax mucoreus (Limnephilidae) use their antennae for olfactory food detection?

Abstract. The behaviour of larvae of Melampophylax mucoreus (Limnephilidae; Trichoptera) is studied to test their capacity for food detection over long distances by olfaction. In aquaria experiments with stagnant water, the larvae rapidly accumulate on a biofilm-covered stone (offered food patch) but not on control stones without biofilm-cover. Larvae in an artificial flow channel (flume), with uni-directional flow between an arrangement of stones covered with biofilm and stones without biofilm, can find food patches upstream from their location more rapidly than downstream. Stimuli transported towards the larvae by the water current might assist food location. However, no significant differences could be found in the movement of larvae with intact antennae compared with larvae without antennae. The results lead to the conclusion that the larvae of M. mucoreus find food patches mainly by random movement, which is assisted by their high mobility. Long-distance olfactory orientation towards food patches, mediated by antennae, can be precluded. Gustatory stimuli appear to play an important role in contact-chemoreception to identify biofilm patches on stone surfaces. Scanning electron microscopy studies of the larval head reveal that the antennae of M. mucoreus are small pegs (50 µm in length) with an apical plate (15 µm in diameter). The mouthparts of the larvae, especially the maxillary palps, show a variety of different sensilla types that are possibly used for contact-chemoreception. These sensilla also could be responsible for the orientation towards a food resource upstream of the larvae.