In 1933, the late Dr. Drysdale Anderson made a series of laboratory experiments at Onitsha, Southern Nigeria, to study the mosquito larva-killing properties of a number of mineral oils and of some mixtures of these oils. For the experiments he used fresh fourth instar larvae of Anopheles costalis, Giles, which is the most common malaria-carrying species in Nigeria; these larvae he obtained from two temporary pools in the bush, which produced large numbers of larvae in wet weather but dried up after a period of 48 hours without rain.

For his experiments Dr. Anderson used plates marked at a diameter of 19-5 cm. (giving a depth of fluid of 2-5 cm.) with 20 to 30 larvae for each plate and one observer for every 3 plates. An experiment consisted of an average of 200 larvae. The oil was applied by discharging 0·65 cc. from a pipette.

It was suggested that confirmatory experiments in the field were required to check the results of these laboratory experiments. This led to the methods described below being devised by us for testing the efficiency of larvicides under conditions as nearly natural as practicable.

To ensure comparability of results we dug our own breeding-pits, each approximately 2 feet by 2 feet square, on low-lying ground where the ground water is very near the surface. The pits were made of such a depth as to contain 8–12 inches of water and are kept under observation for breeding, and when this occurs its intensity is recorded by measuring out a definite number of dips taken along the four sides of the pit and by counting the larvae captured.

For this “dipping” we made our own rectangular dishes of zinc sheeting with sloping sides 2 inches from rim to bottom, 9 inches by 5½ inches in area at rim level, and 8 inches by 4½ inches in area at the bottom. In practice, such dishes collect about 30 fluid ounces at each complete dip.