Biology and Immature Stages of <I>Brachydeutera sturtevanti</I> (Diptera: Ephydridae), a Hyponeustic Generalist

Abstract

Brachydeutera sturtevanti Wirth is a shore fly found commonly in a variety of lentic habitats, including ephemeral pools, in the American Southwest and northern Mexico. We conducted field studies and laboratory rearings to elucidate the morphology and trophic ecology of this colonizer species important 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 substrates, or by bringing their mouthparts to the water surface and creating a vortex to initiate filter feeding. The mouthhooks are modified to form dorsoventrally-flattened plates lined with stout projections that facilitate the versatile larval feeding. The incubation period under laboratory conditions (20–22°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 liter 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 tule extract and algae (TA) illustrated the ability of B. sturtevanti to colonize and complete larval development in habitats varying broadly in food quality. Adults were equally attracted to all treatments and each treatment produced equivalent numbers of puparia. The mean dry weight per puparium formed in each treatment showed an increasing trend of tule extract and algae > A > T > L > C, but dry weights among treatments were statistically equal. These data illustrate the generalist and opportunist nature of B. sturtevanti. The egg, three instars, and puparium are described and illustrated, and a preliminary key to Brachydeutera third instars from North America north of Mexico is given.