A freely breeding colony was allowed to oviposit in clean water and in water containing different concentrations
of decayed vegetable matter. Over 70% of the eggs were laid in the clean water, and fewer eggs were laid as the contamination increased (Surtees, 1960b). It is of interest to note that eggs placed in solutions of contaminated water all hatched, and the larvae developed more rapidly than in cleaner water.
Surface area
When a series of shallow containers was available for egg-laying, varying in surface area from 19 cm2 to 95 cm2, 28% of all eggs laid were found in the largest container, and a direct linear relationship existed between surface area and number of eggs laid (Surtees, 1960c).