Biology and immature stages of Brachydeutera sturtevanti (Diptera : Ephydridae), a hyponeustic generalist

Brachydeutera sturtevanti Wirth is a shore fly found commonly in a variety of lentic habitats, including ephemeral pools, in the American Southwest an d northern Mexico. We conducted field studies and laboratory rearings to el ucidate the morphology and trophic ecology of this colonizer species import ant to newly flooded habitats such as constructed wetlands. The larvae are generally hyponeustic, suspended from the water surface by hydrofuge hairs on the posterior spiracles. All instars exhibit extremely versatile feeding strategies by collecting or scraping algae and detritus from solid substra tes, or by bringing their mouthparts to the water surface and. creating a v ortex to initiate filter feeding. The mouthhooks are modified to form dorso ventrally-flattened plates lined with stout projections that facilitate the versatile larval feeding. The incubation period under laboratory condition s (20-22 degrees C) was 1-4 d; the three stadia lasted 3-5 d each while the pupal period was 6-8 d. The results of a colonization experiment with 15 l iter tubs containing distilled water (controls, C), oligotrophic lake water (L), lake water with a tule extract (T), lake water supplemented with the green alga Chlamydomonas (A), or lake water with both a rule extract and al gae (TA) illustrated the ability of B. sturtevanti to colonize and complete larval development in habitats varying broadly in food quality. Adults wer e equally attracted to all treatments and each treatment produced equivalen t numbers of puparia. The mean dry weight per puparium formed in each treat ment showed an increasing trend of tule extract and algae > A > T > L > C, but dry weights among treatments were statistically equal. These data illus trate the generalist and opportunist nature of B. sturtevanti. The egg, thr ee instars, and puparium are described and. illustrated, and. a preliminary key to Brachydeutera third instars from North America north of Mexico is g iven.