A quantitative analysis of underwater oviposition by the mosquito Mansonia titillans

ABSTRACT. Formation of the rosette-like egg mass of the neotropical mosquito Mansonia titillans Walker is described from video recordings of thirteen females ovipositing on the undersurfaces of water lettuce ( Pistia stratiotes ) leaves in the laboratory. The female abdomen executes symmetrical stroking behaviour to the right and left of centre line. Outstrokes consist solely of scratching, in which spines on the eighth tergite abrade the leaf surface preparatory to oviposition. A row of eggs is glued to the leaf only on instrokes, which are of longer duration than outstrokes, and may be interrupted by scratches and pauses. Scratching precedes oviposition of each of the first four eggs, which are laid without stroking behaviour. The egg mass is enveloped in an air bubble which is transported underwater on the hydrofuge female abdomen. The deposition of eggs on instrokes is homologous to the behaviour used by Culex and Culiseta mosquitoes in the construction of free-floating egg rafts.