Anopheles aconitus Dön. has long been known as an important vector of malaria in Indonesia. More recently it has been shown to be the principal, if not the only vector in the inland areas of Java. A. maculatus Theo. has been regarded as an important vector in hilly regions.

The observations recorded in the present paper were carried out in an inland area in East Java between June 1957 and May 1958, and in a hilly one in West Java between April 1956 and March 1957, and were concerned, in particular, with the resting and feeding habits of these two species in so far as they might influence methods of control.

A. aconitus is found in great numbers throughout the year with a major peak of density from March to May, about harvest time of the first and more extensive rice crop.

In the areas studied, A. aconitus is largely exophilic and, where man is concerned, exophagous, nearly three times as many examples being taken biting man outdoors as indoors, and 17 per cent. of 359 examples taken outdoors were positive for human blood as compared with 5 per cent. of 1,438 examples from all situations. Of the remainder, 93·5 per cent. were positive for ox. On the whole, therefore, this species is highly, though not exclusively, zoophilic and readily enters cattle-sheds, built of bamboo matting, to feed, and, in those sheds that have walls as well as roofs, up to 75 per cent. may remain for at least two hours after having fed, and appreciable but variable numbers of fully fed individuals may remain during day-time.

Most of the feeding on man outdoors took place before midnight, and, on cattle in sheds, between midnight and 0600 hr., with peaks between midnight and 0100 hr. and between 0400 and 0500 hr., respectively. Peak periods of entry into an animal-baited trap were during the second and fourth quarters of the night.

These results differ somewhat from those reported from certain other localities in Java by other workers. There is, therefore, a need for careful repetition, in other areas, of studies of the bionomics and for experiments on the effect on a population of A. aconitus of applications of a residual insecticide.

A. maculatus occurs in the hilly area in considerable numbers throughout the year, and there seems to be no great seasonal fluctuation. This species rests mainly on coffee and palm plants both by day and by night, but readily enters cattle-sheds at night. No blood-meals from this species were subjected to the precipitin test. It is suggested that the importance of A. maculatus in the transmission of malaria needs further investigation.

Over 1,000 examples of A. maculatus and A. aconitus, taken in the hilly area, were dissected, but no malaria infection was found.

A. vagus Dön. is present in the inland area in large numbers during the greater part of the year, with its peak from November to February, during the rainy season. It is more endophilic and endophagous than A. aconitus but is not considered important in malaria transmission.

A. annularis Wulp has its peak in March, and A. kochi Dön. in May. A. barbirostris Wulp, A. subpictus malayensis Hack, and A. tessallatus Theo. were found only in small numbers. All these species are highly zoophilic in the areas studied; they are not considered important in malaria transmission.