Lonchoptera lutea (Lonchopteridae), Panzer, 1809

Rotheray, Graham & Lyszkowski, Richard, 2015, Diverse mechanisms of feeding and movement in Cyclorrhaphan larvae (Diptera), Journal of Natural History 49 (35), pp. 2139-2211 : 2145-2146

Saprophagy: Lonchoptera lutea (Lonchopteridae)

The larva of this species feeds on watery biofilm, i.e. a matrix enclosed, microbial accretion ( Hall-Stoodley et al. 2004) coating smooth substrates, such as fallen leaves, dead wood, stones, etc. where access is restricted+ to ++ ( Table 1). The segments of the rear compartment, anal segment to the metathorax, are up to 3× wider than long, dorso-ventrally flattened and protected by sclerotised, dorsal plates. The ventral surface is coated in spicules. The plates of the anal and seventh abdominal segment and the metathoracic and first abdominal segment are fused. The front compartment, mesothorax to the head, is cylindrical and narrow relative to the rear compartment ( Figure 2 ). The head is an open trough, the sides of which each bear an antenna and a maxillary organ ( Figures 3A and 3B ). The apex of the trough has a bar-shaped, labial lobe on each side of which is an extrudable, tapered, setae-coated projection. Extending from the head skeleton into each side of the trough is a sclerotised rod, the parastomal bars of higher Cyclorrhapha and into the floor of the trough, paired labial rods which are joined by a lightly sclerotised strip, the ventral bridge of higher Cyclorrhapha . Each mandible consists of three or four sclerites which are not in the same plane ( Figure 3B ). The first sclerite articulates with the labial rods, the next two change plane and extend up through the fleshy sides of the trough and end in a large, oval-shaped sclerite. From this oval sclerite is a short projection orientated in another plane, at the end of which is a hook ( Figure 3B ). The hooks form an arch over the opening to the pharynx, at the base of the trough ( Figure 3A ). Cibarial ridges are present.

In feeding, this larva sweeps and lunges repeatedly at a rate of about one lunge per 0.1 sec (Film 2, Figures 4A–D ). Lunges consist of the front compartment extending down and across the substrate by which action biofilm is shovelled on to the trough ( Figure 4A ). During shovelling, the extrudable lobes swung round in front ( Figure 4B ), the trough tilts up and the oval mandibular sclerite twists backwards, the mandibular hooks elevate, the sides of the trough flick backwards and the pump in the basal sclerite sucks biofilm into the pharynx (Films 2–3, Figures 4C and 4D ). Action of the pump is revealed by inward movement of the dorsal cornua and there is one pumping action per lunge (Film 3). The head skeleton is fixed and does not protract or retract (Film 4). The dorsal plates are inflexible and do not fold during locomotion, but raise and lower in relation to the position of the peristaltic movement wave. Direction changes are due to the front compartment pressing against the substrate at an angle relative to the previous position. Alternatively, S-shaped, sideways motion occurs. With the anal segment and the pseudocephalon gripping the substrate, opposing contraction/expansion of the lateral margins of the first few abdominal segments presses one side against the substrate while the other expands, lifts and lowers. When the expanded side touches the substrate, inducing a characteristic rocking motion, the prothorax and pseudocephalon move to a position lateral to the start position and by repetition of these movements, the body shifts sideways (Film 2). This larva is unable to make sharp changes in direction, twist round and it avoids moving on narrow substrates, such as leaf petioles. It is, however, able to squeeze through spaces less than its height, such as between wet, overlapping leaves.

Figures

Figure 2. Lonchoptera lutea, larva with extended front compartment, still from a film. p = prothotax; m = mesothorax; m+a1 = fused metathorax + first abdominal segment.

Figure 3. Lonchoptera lutea, head skeleton. (A) Lonchoptera lutea, head skeleton. pseudocephalon and apex of head skeleton, still from Film 3. a = base of antenna; db = dorsal bridge; lb = labrum; m = mandibular hooks; mx = maxillary organ; pb = parastomal bar; (B) drawing of the mandible and articulation with the labium. b = basal mandibular sclerite(s); lr = labial rod; o = oval mandibular sclerite; m = mandibular hook; v = ventral bridge.

Figures 4. Lonchoptera lutea, feeding on biofilm coating dead wood, stills from Film 2. (A) Pseudocephalon lowered into biofilm; (B) extrudable cones swing round to front of pseudocephalon; (C) pseudocephalon lifted up; (D) limit of pseudocephalon lifting.