24 MOSQUITO WORK IN KHARTOUM, ETC.

Distribution of genera in Khartoum

Reinfection by steamer bred mosquitoes

Mosquito Maps

Culex fatigans is ubiquitous, but is chiefly, as has long been known, a domestic variety. It is the well mosquito par excellence, and consequently is found all

over Khartoum, from the steamers back to the cemetery and Gordon s old ramparts, and from the British barracks in the east to the Zoological Gardens in the west. It also loves river pools, garden tanks, and bath-waste pits, and will breed in almost any kind of dirty water, even in that streaked with oil,

as found in steamer engine rooms.

Py retop horns costalis, on the other hand, is not domestic, and its range was found to be limited. It chiefly occurred in the various water collections rendered necessary by the irrigation of the Palace Gardens. It was found in those which were not stocked with fish, and especially in valve pits and shallow, reedy pools. It seemed indifferent to the presence of frogs. This mosquito has also been found in garden tanks along the river front, in the pools left by the falling Kile, in the sakia pits of the Gordon Gardens, and in a few, a very few, wells. It was present in considerable numbers in the Palace Gardens, and infested the neighbouring houses, but it does not appear to fly far from the shelter of vegetation, nor has it ever been found breeding on board steamers at

Khartoum, partly because it is somewhat fastidious in its tastes, and prefers natural collections, and partly because the larva? require plenty of light.

Stegomyia fas data again, is the great steamer mosquito, and has not been found to breed much in Khartoum itself. It is to be remembered, however, that the larvae of this genus differ somewhat in habits from those of the other genera. They are more worm-like, hug the bottom and come only infrequently to the surface, consequently they may have been more often missed. It has been found breeding in the zeers and a few other water collections, but very rarely in the wells. Further, and this is interesting, it seemed to be almost wholly confined to what may be called the front belt of the town, the river zone, and hence my belief that it was very largely an unwelcome gift from the steamers. Certain wells, opposite which steamers were accustomed to lie up, for example at the post office, (see page 19) constantly became reinfected with Culex after they had been treated and freed, and these also I believe came from the boats. Indeed it has been found much easier to keep the south part of the town free than that which borders the Blue Kile.

The accompanying maps show the respective distribution, and also exhibit another point, the effect of the treatment.

Map Ko. 1 represents the condition of the various water collections as found during the first complete round of the town made in August and the first part of September, 1903.

Map Ko. 2 shews the same collections and any new ones which may have been discovered or been formed (for new wells are constantly being sunk), after the necessary oilings. Different marks have been devised to explain different conditions so that the improvement which has resulted may be seen at a glance. The second map brings us down to the end of the summer (October 31st) and the summer work, thus excluding any fallacies which might arise from altered climatic