Structure and protective devices of the egg of the mosquito Culex pipiens.

Abstract

Abstract The structure and function of the egg shell of Culex pipiens L. is described. The outer layer of the shell consists of two sheets that hold a film of air between them. The film of air functions as a plastron when the egg is submerged in water. The outer sheet is an open hydrofuge network except near the anterior pole. Single eggs and rafts of eggs distort the surface film in different ways, and differences in their behaviour can be accounted for by differences in the way they make use of the surface tension of the water. The egg is protectively coloured: it is dark above and pale beneath. The pale colour of the under-surface is produced by light reflected from a water-air interface. The reflecting surface beneath erect eggs is on the anterior cup. The reflecting surface beneath eggs floating on their sides is the plastron water-air interface. On the posterior pole of each egg there is normally a drop of liquid. This liquid is shown to be a defensive fluid in experiments with two species of ants, which are natural enemies of the eggs. The defensive fluid is of maternal origin. It is kept wetted by water translocated from the anterior pole in contact with the water through the substance of the outer layer of chorion.