OVIPOSITION BEHAVIOR, EGG-MASSES AND HATCHING RESPONSE OF THE EGGS OF 5 NEARCTIC SPECIES OF SIMULIUM (DIPTERA, SIMULIIDAE)

The oviposition behaviour of Simulium decorum Wlk., S. vittatum Zett., S. verecundum Stone & Jamnback and S. vernum Macq. is described, with emphasis on the approach by the females to the egglaying sites, the substrates selected and the behaviour of the flies while laying. The eggs and egg-masses of these four species and S. longistylatum Shewell are described; the eggs can be distinguished on the basis of size, and a key is provided to aid their identification. Eggs of S. vittatum completed embryonic development and hatched more quickly than those of S. verecundum of the same age at both 15 and 24°C. The hatch rate of the eggs of both species exceeded 90% when the eggs were present in single-layered masses. The position of an egg Within a multi-layered mass had an important effect on its ability to complete development; significantly lower proportions of eggs of both S. verecundum and S. vittatum in the lowermost layers of large egg-masses hatched, compared with the hatch of those in the top layer. The location of an egg within an egg-mass must be considered a major factor of mortality in the egg stage. The eggs of neither S. verecundum nor S. vittatum were resistant to drying; mortality due to desiccation was related to both the duration of the drying period and the stage of embryonic development when they were subjected to drying. © 1979, Cambridge University Press. All rights reserved.