Polyporivora picta (Platypezidae)

Rotheray, Graham & Lyszkowski, Richard, 2015, Diverse mechanisms of feeding and movement in Cyclorrhaphan larvae (Diptera), Journal of Natural History 49 (35), pp. 2139-2211 : 2147-2148

Mycophagy: Polyporivora picta (Platypezidae)

This larva excavates tunnels through fruiting bodies of the fungus, Trametes versicolor (L.) Lloyd ( Polyporaceae ) where access is restricted+++ ( Table 1). Rear compartment segments, anal segment to the metathorax, are subcyclindrical in cross-section and coated in transverse rows of spicules ( Figure 5 ). Segments of the middle compartment, mesothorax to the pseudocephalon, are wedge-shaped. Pseudocephalon is retractile and small, only about two thirds as high, half as long and less than half as wide as the prothorax. From the ventral margin of the pseudocephalon extends an elongate, sclerotised, oral plate, nearly as long as the head skeleton ( Figure 6A ). The front compartment is the retractile head skeleton which lacks cibarial ridges. Apically, it has three pairs of conspicuous labial teeth ( Figures 6 and 7 ). A gap exists between the rows of teeth ( Figure 6B ) and on either side of the upper two pairs of teeth are the poorly sclerotised, transluscent mandibles, which articulate with the labium posteriorly and have a serrated apical margin ( Figure 7 ). The entrance to the pharynx is between the upper pair of teeth.

To feed the larva grips the tunnel with the rear compartment and lunges against the face. Lunges consist of the middle compartment contracting and raising and the head skeleton retracting; these actions place the exposed, labial teeth high in the tunnel. Extending and lowering from these contracted states presses the labial teeth into and moves them down across the tunnel face, and the space between the rows of labial teeth fills with loosened and torn fungal hyphae and, if necessary, the mandibles depress to guide them towards the pharynx where they are sucked in by the pump. Ensuring the labial teeth are fully exposed during lunging, the ventral part of the pseudocephalon is pulled backwards and out of the way probably by contraction of muscles attached to the oral plate. Peristaltic waves keep the larva pressed up against the tunnel face. Differential contraction of the lateral margins enables the front end to alter the direction of lunging and to excavate a tunnel wide enough for the body to pass through. Tunnels extend many times body length and curve gently sideways or up or down. They penetrate the fungus in all directions and open out on both the dorsal and ventral surfaces.

Figures

Figure 5. Polyporivora picta, preserved puparium, lateral view, head to the right, length 5 mm.

Figures 6. Polyporivora picta, head skeleton from a puparium. (A) Lateral view, labial teeth to the right, length 0.6 mm; (B) apical view of labial teeth.

Figure 7. Polyporivora picta, labial teeth and mandible with serrated margin outside the upper two labial teeth.