Meiosimyza platycephala (Loew) (Lauxaniidae

Rotheray, Graham & Lyszkowski, Richard, 2015, Diverse mechanisms of feeding and movement in Cyclorrhaphan larvae (Diptera), Journal of Natural History 49 (35), pp. 2139-2211 : 2168-2169

Meiosimyza platycephala (Loew) (Lauxaniidae )

and Clusia flava (Meigen) (Clusiidae)

These larvae feed on watery biofilm coating relatively smooth substrates where access is restricted + to ++ ( Table 1). The oral cavity of M. platycephala is closed by a fleshy bridge, its surface coated with eight transverse rows of conspicuous, upstanding, apically sclerotised seta-like projections which also cover the inflated sides of the pseudocephalon and either side of the mandibular hooks ( Figures 33A and 33B ). This larva gathers food into the oral cavity by brushing with these setae (Films 1 and 15). The mandible base is narrow and elongate and the atrium is wide relative to the width of the mandibles ( Figure 34 ). The atrium is supported dorsally by the sclerotised apex of the epipharygneal plate and cibarial ridges are present. When feeding the larva sweeps from side to side (Film 1, Figures 19A–C ) and lunges repeatedly; the lunge distance is fairly short and the lunge time not particularly fast or slow ( Table 2). Throughout lunging, the mandibles are inclined and parallel, i.e. they do not elevate and only depress over the range 20–70 degrees ( Table 2), and they do not separate by much (Film 15, Figure 34 ). When feeding, the larva avoids obstacles such as prominent leaf veins. However, it crosses over such obstacles during locomotion, is able to make sharp changes in direction, such as over the edges of overhanging leaves, and by flattening its body can squeeze between adhering leaves.

Clusia flava : prothorax ovoid with a flattened apex surrounded by sensilla with antennae and maxillary organs almost flat to the surface ( Figures 35–37 ). The centre of this apex leads to the inverted pseudocephalon from which project the tips of the lightly sclerotised mandibular hooks. This larva feeds by spot-sucking watery biofilm coated and soaked into soft, decayed, annual layers of sapwood of dead trees and branches ( Table 1). Apart from the mandibular hooks, the head skeleton lacks sclerotisation, is translucent and short ( Table 3). Like the pseudocephalon, it is fixed in an inverted position and does not protract or retract. The intermediate sclerite is fused to the basal sclerite, and cibarial ridges and dental sclerite are absent. Unusually, the anterior and ventral margins of the mesothorax and metathorax are coated in spicules; spicules also coat much of the ventral and dorsal margins of the rear body compartment. Apart from an inverted head skeleton, this larva is remarkable for its slow movement and highly flexible, middle body compartment (Film 16). The middle body compartment can twist from side to side, rotate 360 degrees, and each segment can collapse and fold into the one behind. Feeding lunges consist of the middle compartment bending down and the apex of the prothorax being placed on to the substrate and remaining in this position for up to 4 minutes.

Figures

Figures 19. Meiosimyza platycephala, sweeping on the surface of a dead leaf, stills from Film 1 of a sequence lasting 12 sec in real time. (A) Limit reached of sweeping right; (B) sweeping back to the midline; (C) sweeping left.

Figures 33. Meiosimyza platycephala, preserved larva, pseudocephalon; (A) lateral view; (B) ventral view, length 0.2 mm.

Figure 34. Meiosimyza platycephala, anterior end, dorsal view, still from Film 15.

Figure 35. Clusia flava, preserved larva, lateral view, head to the right, length 8.7 mm.

Figure 36. Clusia flava, thorax, position at maximum forward extension, dorsal view, still from Film 15.

Figure 37. Clusia flava, prothorax, apical view still from Film 15.