| Abstract: |
At Madhyamgram, near Calcutta, 61 rice plots were examined for anopheline larvae once a week from June to October and at Sonarpur, a few miles away, 136 plots were examined once a fortnight from July to December during two consecutive rice seasons. Larvae of 11 species were found: Anopheles philippinensis, the local malaria vector, A. hyrcanus var. nigerrimus, A. barbirostris, A. annularis, A. ramsayi, A. pallidus, A. tessellatus, A. varuna, A. aconitus, A. vagus and A. subpictus, In fallow fields A. vagus and A. subpictus occurred and a few A. hyrcanus var. nigerrimus. In cultivated fields at Sonarpur all 11 species were present while at Madhyamgram A. aconitus and A. tessellatus were absent. During the transplanting season larvae of A. vagus and A. subpictus persisted in the muddy water
the other species began to appear as the silt settled. At the beginning of the season when shade was absent the water temperature occasionally reached 42°C. and over and in such conditions only the larvae of A. hyrcanus var. nigerrimus and A. vagus were found. As the rice grew and provided more shade, larvae became more numerous
most were found in water 2 to 12 inches deep and where the rice was 1 to 2 feet in height. Larvae of A. philippinensis first appeared when the rice was 15 inches high but disappeared again after it reached 2 feet in September. Harvesting of the rice in October and November disturbed the environment and increased the organic contamination of the water in which only larvae of A. hyrcanus v. nigerrimus and A. annularis could then be found. A. philippinensis is the only natural vector of malaria in these areas and the author feels that he has shown by these studies that rice fields are not nearly so dangerous as are the permanent ponds in villages, where the breeding of this species is particularly prolific. H. S. Leeson.
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