Species Composition and Life Histories of Aquatic Insects in a Lowland Sonoran Desert Stream

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Abstract
From July 1977 to Nov. 1979, 99 taxa of aquatic insects and a total of 104 macroinvertebrate taxa were collected in Sycamore Creek; Arizona. The fauna is primarily composed of organisms restricted to southwest USA, although many widespread Nearctic taxa are also present. Life histories of 17 taxa were examined with emphasis on total developmental time (egg to adult), reproductive period and dormancy. Ephemeroptera, small Diptera and the corixid Graptocorixa serrulata developed rapidly (1-3 wk) and reproduced continuously. Aquatic beetles (Dytiscidae and Hydrophilidae) developed in 4-8 wk and reproduced only in spring and after summer rains. Trichoptera (2 spp.) required 6-7 wk for development and reproduced continuously. Degree-day developmental rates (ca. 1200) were similar for some desert and temperate species. Dormant stages were restricted to stoneflies (egg diapause) and tabanids (larval diapause). Drought and flooding markedly influenced life histories. Adaptations to drought are habitat selection by ovipositing adults and rapid development. Adaptations to floods are behavioral avoidance, rapid development and seasonal reproduction. Floods also contribute to the rarity of dormancy; aerial adults become the life stage resistant to disturbance. Floods, which do not occur in temporary lentic systems, are an imporant selective pressure in temporary lotic systems.