EGG AND LARVAL DEVELOPMENT TIMES FOR 35 SPECIES OF TROPICAL STREAM INSECTS FROM COSTA-RICA

We examined total development times for 5 mayfly species, 2 stoneflies , 10 caddisflies, and 18 chironomid midges collected from three stream s that now through tropical evergreen forest in northwestern Costa Ric a. Most eggs, larvae, and pupae were reared in the laboratory in a pho toperiod of 12:12 LD and at 20 degrees C, which simulated field condit ions. Algae, algal detritus, and leaves were provided as food for all species; predators were also given various animal prey. All study spec ies had total development times that were rapid relative to the univol tine life histories observed or assumed for many temperate species. Eg g development times ranged from a few days to approximately a week for chironomids and from 10 to 38 days for mayflies, stoneflies, and cadd isflies. Most chironomids had short larval/pupal development times: de velopment was completed in 19-29 d by seven species, in 30-40 d by nin e species, and in >50 d by two species. Relatively short development t imes (including the pupal stage when present) were also observed for t he mayfly Acerpenna sp. (28 d) and the caddisflies Wormaldia sp. (45 d ) and Oecetis nr. prolongata (52 d). Larval/pupal development times we re longer for the other four mayflies (76-159 d), two stoneflies (83-1 67 d), and eight caddisflies (72-209 d). No evidence of egg or larval diapause was observed. The combination of rapid development and absenc e of diapause suggests that all these species have multivoltine life h istories. This finding has important implications for temporal changes in the structure and function of the aquatic insect assemblage in the se streams.