The combined effects of temperature and food consumption on body weight, egg production and developmental time in Chaoborus crystallinus De Geer (Diptera: Chaoboridae) : Some new evidence for the adaptive value of vertical migration.

Chaoborus crystallinus fourth-instar larvae were reared individually at 14°, 17° and 20° C under different food conditions. Daphnia magna of 1.25 mm average length served as prey. The following were measured: amount of prey ingested, larval weight gain, duration of fourth instar, body weight of the adults, and egg number per female. At a given temperature, the body weight, egg-number and developmental rate increased with food consumption. At a given food consumption, higher temperatures caused a decrease in body weight and egg number, and an increase in developmental rate. Gross production efficiencies for fourth-instar larvae were highest at temperatures around 17° C. The results clearly indicate that from an energetic point of view higher temperatures are disadvantageous. In C. crystallinus vertical migration is evidently a way of lowering the temperature to which the animals are exposed and hence optimizing food conversion into biomass and offspring production, especially if prey densities are below the saturation level.