M 147
Few A. hyrcanus were caught in the night catches and fewer still in day catches. The chief breeding place of A. hyrcanus, namely, the rice ravine was a good distance from the tent and there were numerous huts in between.
As in 1932 A. jeyporiensis was absent from the catches made during the period April-September inclusive. In 1932, comparatively large numbers were obtained during the last quarter of the year. The locality was visited in November 1932 when the rice had been cut and water in the ravine was draining off. In it were found numerous larvae of A. jeyporiensis and A. hyrcanus.
In October 1933 when the ravine was inspected the water was being drained off, but the adjacent ditch previously mentioned had been both deepened and widened. On enquiry it was ascertained that rice cultivation was to be discontinued for economical reasons, and that vegetables were to be grown instead, after suitable drainage. Another visit was paid after the rice had been cut, but owing to the operations on the ditch very little water was left in the rice fields as compared with the amount found in the previous year; however, 93 larvae of A. jeyporiensis and 121 of A. hyrcanus were collected. It would seem that as at Shing Mun, drainage preparatory to cutting the rice makes the water suitable for A. jeyporiensis, which continue to breed while it is draining off. Drainage is not done when the first crop is cut, but the stubble is ploughed in, and another crop planted, hence no adults were obtained at that period as the water was not apparently suitable for the larvae. It would also appear that hill streams do not affect the catches of A. jeyporiensis to any extent.
Table XI gives the results of dissections for malarial infection. In A. minimus it was highest in June, July, August and usually high in December—6% as compared with 1.6% in the previous year.
Table XII gives the result of dissections for filarial infection of mosquitoes captured. In November and December 25 A. minimus were obtained which had recently fed, the midgut was opened and the red blood corpuscles examined—none were nucleated, therefore these Anophelines had fed on mammalian blood only.
(2) Shing Mun Camp.
The coolie lines were divided into two sections, separated by a narrow ridge, one section being situated in a ravine marked A in the map, the other section in a ravine forming a branch of stream B2. Streams abound on all sides of the camp. There was a certain amount of rice cultivation, shown in the map as shaded areas. The rice fields in the Shing Mun Valley above the site of the Dam had been abandoned for a considerable period previously.