1. A sketch is given of the Malaria Control Organisation in Service areas in Mauritius with a summarised history of malaria work in the Island since the first epidemic in 1865.2. Keys to Mauritian Anophelines and their larvae with notes on their field recognition characters are followed by data on the distribution of adult Anophelines in the Colony and their relation to malaria intensity in different areas. A. melas appears to be absent from coastal swamps.3. The influence of a number of environmental factors is discussed. It is concluded that temperature is an important limiting factor generally in winter and perennially in the highlands (above 1,000 ft.), but that the flushing action of heavy rains and probably the precipitation of food supply by colloidal iron moving under high rainfall conditions (over 100 ins.) from ferrugineous lavas both play their part in the natural control of A. funestus and A. gambiae.The behaviour of A. gambiae with respect to temperature is expressed by an area enclosed by two symmetrical catenary curves, that illustrate well the adverse influence on development of low temperatures normally occurring in winter on the coast and all the year round in the residential uplands above 1,000 ft. The thermal death point of A. gambiae larvae is about 42°C. and that of A. funestus 40°C. and the lower limit of larval activity is 16·5°C. A. gambiae develops most rapidly at an estimated temperature of about 37°C.

There are three moth-borers of sugar-cane in Mauritius, Proceras sacchariphagus Boj. (Crambid.), Sesamia vuteria (Stoll) (Agrotid.) and Olethreutes schistaceana (Snell.) (Olethreutid.).The eggs of all three are parasitised by Trichogramma sp. ? australicum Gir., while a second undetermined species of Trichogramma parasitises the eggs of Sesamia and Olethreutes. Sesamia eggs are also parasitised by a Scelionid, Platytelenomus sp. ? hylas Nixon.

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