ECOLOGY AND POPULATION BIOLOGY Biology and Immature Stages of Brachydeutera sturtevanti (Diptera: Ephydridae), a Hyponeustic Generalist J. B. KEIPER AND W. E. WALTON Department of Entomology, University of California, Riverside, CA 92521 Ann. Entomol. Soc. Am. 93(3): 468Ð475 (2000) ABSTRACT Brachydeutera sturtevanti Wirth is a shore ßy found commonly in a variety of lentic habitats, including ephemeral pools, in the American Southwest and northern Mexico. We con- ducted Þeld studies and laboratory rearings to elucidate the morphology and trophic ecology of this colonizer species important to newly ßooded 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 Þlter feeding. The mouthhooks are modiÞed to form dorsoventrally-ßattened plates lined with stout projections that facilitate the versatile larval feeding. The incubation period under laboratory conditions (20Ð22ЊC) was 1Ð4 d; the three stadia lasted 3Ð5 d each while the pupal period was 6Ð8 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 supple- mented 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 Ͼ A Ͼ T Ͼ L Ͼ 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. KEY WORDS Brachydeutera sturtevanti, shore ßies, larval feeding habits, r-strategist, wetlands, keys THE BIOLOGY OF shore ßies (Diptera: Ephydridae) has adventive species from the Oriental region and re- received considerable attention by entomologists and mains unreared; no biological observations have been ecologists; however, the immatures of most species published for this species (Mathis and Steiner 1986). remain unknown. These small ßies exploit many tro- The third instars of B. hebes (Williams 1938), B. phic and spatial niches in aquatic ecosystems, and argentata (Johannsen 1935), and B. neotropica (Liz- although some exhibit specialized feeding or micro- arralde de Grosso 1972) have been described, whereas habitat preferences, larvae of many genera use a broad those of B. longipes and B. sturtevanti have not. No spectrum of resources (Foote 1995, Courtney et al. published information on the morphology of early 1996). The genus Brachydeutera Loew contains 15 instars of Brachydeutera is available. Herein, we give species worldwide (Mathis and Zatwarnicki 1995) and information on the biology and morphology of all is represented by Þve species in North America and immature stages of B. sturtevanti from southern Cal- Hawaii (Williams 1938, Mathis and Steiner 1986). Lar- ifornia. We also present the results of an experiment vae are present in a variety of lentic habitats and that addressed the hypotheses that adults are not se- appear to be trophic generalists. Adults and larvae are lective in their use of water containing different po- found at the water surface, usually among emergent tential larval food sources as breeding sites, and that vegetation. Williams (1938) reared B. hebes Cresson in the mean time until formation of the puparium and Hawaii and reported that larvae scraped materials pupal mass are equal regardless of the food source from dead and living leaves, consumed algal Þlaments, provided to larvae. Species of Brachydeutera appear to and scavenged dead animal tissues. Brachydeutera ar- be important colonizers, and frequently we have ob- gentata (Walker) (Johannsen 1935) and B. neotropica served B. sturtevanti adults and immatures in large Wirth (Lizarralde de Grosso 1972) also exhibit scav- numbers in newly ßooded habitats. Constructed wet- enging habits. Scheiring and Foote (1973) reared B. lands are becoming common in the arid southwestern sturtevanti Wirth on decaying lettuce; the larvae prob- United States (Walton and Workman 1998), and ably obtained most of their nutriment from associated knowledge of the natural history and feeding ecology microorganisms. Brachydeutera longipes Hendel is an of early colonists is important to understanding the 0013-8746/00/0468Ð0475$02.00/0 ᭧ 2000 Entomological Society of America May 2000 KEIPER AND WALTON:BIOLOGY OF B. sturtevanti 469 community structure and ecosystem processes of Dishes were examined daily for larval hatch and sub- these anthropogenic environments. A preliminary key sequent larval development. Larvae were observed to species of Brachydeutera larvae from North America with a dissecting microscope at 6Ð50ϫ with a Þber- north of Mexico is given to provide ecologists a means optics light source at the lowest setting needed for to identify Þeld-collected larvae, and to provide mor- observation to avoid altering larval behavior. Duration phological comparisons among species to shed light on of the incubation period and each stadium was deter- the systematics of the genus. mined by direct observation of eclosion and molts, respectively. Only specimens killed in near boiling water and Materials and Methods Þxed in KahleÕs solution were used for description and Adults were taken in several areas of Riverside illustration. Immature stages were placed in petri County, CA, during this study. Several hundred were dishes of 70% ethanol, and tagged image format com- collected at the Hemet/San Jacinto Multipurpose puter Þles were obtained using a low-light camera Treatment Wetlands, an assemblage of constructed (Optronics Engineering DEI-470; Goleta, CA) at- wetlands supplied with secondary efßuent from a tached to a Wild MZ8 dissecting microscope and Im- nearby sewage treatment plant (Walton and Work- age Pro Plus software for an IBM personal computer. man 1998). Flies were pan trapped (Southwood 1978) Tagged image format Þles were printed and then and swept with an aerial net from around the periph- traced on a light table or used as a reference to facil- ery of stands of tules [Schoenoplectus californicus itate illustration. The cephalopharyngeal skeleton and (Meyer) Soja´k]. Approximately 200 were collected spiracles were dissected from specimens cut in half from the Prado Constructed Wetlands near the city of longitudinally from the breathing tube to the met- Corona; these wetlands were supplied with water di- athoracic segment and placed in 10% KOH overnight. verted from the Santa Ana River. Adults were taken Dissected materials were neutralized with a drop of from stands of tules and cattails (Typha spp.). The glacial acetic acid, and slide mounted with Canada University of California-Riverside Agricultural Exper- balsam. Tagged image format Þles of dissections were iment Station is the location of a diverse array of obtained using the low light camera attached to a shallow mesocosms designed for the study of aquatic compound microscope at 100Ð400ϫ. entomology; adults were taken while resting on the To determine if adults were differentially attracted water surface or positioned on ßoating algal mats. The to newly inundated habitats with different potential last, and the most ephemeral habitat studied, was shal- larval food sources, 25 black plastic tubs (15 liter), low pools at the margins of the Colorado River Aq- each containing 8 liters of water, were arranged ran- ueduct near the city of Whitewater. These pools were domly in Þve rows of Þve at the University of Cali- formed when the level of the aqueduct receded, and fornia-Riverside Agricultural Experiment Station on water puddled in concavities of the rocky shore. 30 April 1999. Each tub was separated by 2 m. Treat- Immatures were usually located by hand at the ments were lake water only (L), lake water with a tule water surface near vertical structures such as emer- extract (T), lake water spiked with a culture of the gent vegetation and along the edges of mesocosms; unicellular green alga Chlamydomonas spp. (Chloro- larvae and pupae were collected with small mesh phyta) (A), tule extract coupled with the Chlamydo- scoops, whereas some specimens were collected with monas inocula, and control tubs (C) containing dis- standard 300-ml dippers during routine sampling for tilled water. Lake water obtained from holding ponds mosquitoes. Eggs were sometimes taken from ßoating on the premises that supported low densities of plank- algal mats where adults were observed to congregate. tonic algae (Ϸ700 cells per milliliter) and was sieved Field-collected immatures were saved for rearing, through a 1-mm mesh to remove large particles. The preserved in the Þeld with 50% ethanol (dips), or tule extract was prepared by adding 90 g of dried S. killed in near boiling water, Þxed in KahleÕs solution, californicus to 20 liters of lake water and left to incu- and preserved in 70% ethanol. Larvae saved for rear- bate at