An investigation into the behaviour of Anopheles parensis Gillies at Malindi on the Kenya coast

Extract

In investigations made in January to November 1962, Anopheles parensis Gillies was found biting man in large numbers in a zone near Malindi, Kenya, in which house-spraying with DDT had been carried out between March 1961 and October 1962. Densities were greatest just outside villages, less so on the verandah of a house and least indoors. In one open type of unsprayed house, however, moderately large numbers were caught. The monthly average catch per night by two men was greatest (over 200) outdoors in July and August.

Biting activity reached two peaks during the course of the night, catches in all situations being greatest during the two hours following sunset and the three hours preceding sunrise. The evening peak was highest in the outdoor catches, and the late-night peak in the indoor collections. A distinct influence of moonlight on the catches was observed, the early evening peak under certain conditions being greater during the moon's first quarter and the late-night peak during its last quarter.

Numbers of examples were caught biting cattle, but owing to the absence of large herds of stock it is believed that most feeding took place on man. The proportion of nulliparous females was 64 per cent, in the sprayed zone and 50 per cent, in an unsprayed village, and in the latter the nulliparous rate in females resembling A. funestus Giles (the majority of which would have been that species) was 24 per cent. No specimen of A. parensis infected with sporozoites was found in the sprayed zone. In the unsprayed village, no infected glands were found in a small series dissected. Thus no evidence was obtained that A. parensis was acting as an exophilous vector of malaria in the sprayed zone. Moreover, in view of the high nulliparous rate observed in the unsprayed area, this species is considered unlikely to be of any importance under normal conditions.