Biology and Immature Stages of Parydra quadrituberculata (Diptera: Ephydridae)1

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Abstract
Adults of Paryda quadrituberculata, distributed in North America east of the Rocky Mountains, occur most abundantly in mud- and sand-shore habitats where they feed upon stranded motile, benthic diatoms. Adults use the labellar canalicular processes for scooping and fanning diatoms into the mouth, or prestomum, whereas larvae use their rapidly protracting and retracting mouthhooks to dislodge and move diatoms close to the mouth into which they are sucked by cibarial action. Adults exhibit a definite activity rhythm consisting of searching/feeding, cleaning, and resting with intervening periods of copulation and oviposition during the daylight period followed by “roosting,” or sheltering upon vegetation or prominent objects at twilight. Heavy rain during daylight elicits “roosting” activity. Eggs are laid on emergent objects in conterminal masses of 2–16 and covered by a thin, uniform, green or yellow-green fecal layer, which turns white in old egg masses. Sparsity of emergent objects on mud flats frequently leads to extensive, multiparental encrustations of egg masses. The incubation period lasts 2–5 days. Serial longitudinal sections of 24 second- and 3rd-instar larvae revealed guts packed with diatoms. The larval stadia total 10–23 days and the puparial phase lasts 5–9 days (or much longer in overwintering forms). Pupation occurs in mud with the postanal elongation bent upward and the bifurcated posterior tracheospiracular siphons projecting slightly above the mud surface. At moderate latitudes, both puparia and adults overwinter, but winter collecting indicates that the adult is the main overwintering stage. The adults typically shelter deep in shoreline grass and sedge hummocks. Some gravid females overwinter and adults in general feed and fly during still, sunlit winter days when the air temperature is above 3.3°C. The primary mortality agents are believed to be parasitic Hymenoptera, weather, and shore birds. Urolepis rufipes (Pteromalidae), Hexacola spp. (Cynipidae), Asobara sp. (Braconidae) were reared from puparia. Aggregation of larvae in isolated, drying mud pools was frequently observed, and it is surmised that this aggregation facilitates parasitization. The egg, 3 larval instars, and puparium are described and illustrated.

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