Dormancy, embryogenesis, and hatching of eggs of Prosimulium kiotoense (Diptera: Simuliidae) under natural and experimental conditions.

The egg dormancy and embryogenesis of the univoltine black fly, Prosimulium kiotoense Shiraki, in southwestern Japan were examined under natural and laboratory conditions. Eggs laid in April remained dormant until August (approximately 14 wk after oviposition). Hatching commenced in early October (after 23 wk), when air and water temperatures decreased to 20 and 15 degrees C, respectively, and continued until mid-December (32 wk) in the field. Laboratory experiments showed that lower temperatures (10 and 14 degrees C) supported embryogenesis similar to that observed in the field. In contrast, higher temperatures (18 and 22 degrees C) retarded or completely suppressed embryogenesis after the termination of dormancy. However, completion of dormancy was accelerated when eggs were exposed experimentally to these higher temperatures for 3-12 wk, then returned to a constant low temperature (14 degrees C). Daylength did not affect the maintenance and termination of dormancy. Therefore, temperature played an important role differentially affecting completion of dormancy and postdormancy development. Variable lengths of developmental periods among egg batches under the same conditions indicated possible genetic control of dormancy intensity.