INSECTS INJUEIOUS TO MAN AND STOCK IN ZANZIBAR. 303 



The Mosquitos of Zanzibar Town. 



Anopheles costalis, Lw. The only Anopheline taken in the town area. 

 Larv'ae are generally found in shallow pools rich in decaying vegetation and algal 

 growth, occasionally in water fountains, tin drums, rain-water left in dug-out canoes 

 and crab-holes. They are able to thrive in pools exposed to direct sunlight. Larvae 

 in captivity are difficult to rear, unless under suitable and natural conditions ; 

 many become infested with Vorticella and speedily succumb to this infection. This 

 is the common vector of malaria in Zanzibar, and sporozoits have been found on 

 several occasions in the salivary glands. A. funestus, a much rarer species, has 

 not yet been found infected, but only a small number of adults have been captured. 



Stegomyia fasciata, F. This species is to be found everywhere, breeding 

 under the most varied conditions, generally in household utensils, old tins, earthen- 

 ware jars, etc. They show a marked preference for clear water, being rarely taken 

 in association with Culex fatigans. Some of their rarer haunts are holes in mango 

 trees and slots cut in the trunks of coconut palms to facilitate climbing. The 

 larvae of S. fasciata are very hardy and able to exist in water with a very poor food 

 supply. Experimentally larvae mature and pupate in water to which 2% of sea- 

 water has been added. Adults fed on a patient showing numerous microfilariae 

 {Filaria hancrofti) in his peripheral blood exhibited microfilariae in the thoracic 

 muscles nine days afterwards. Specimens of S. fasciata have been captured on 

 several occasions showing a natural thoracic infection with microfilariae. 



Stegomyia vittatn, Big. (sugens, Theo., nee Wied.). Larvae were found on 

 one occasion in a large dirty pool in a poultry run. 



Culex fatigans, Wied. The commonest mosquito in all quarters of both 

 towns. The larvae are nearly always found in water rich in decaying animal or 

 vegetable matter, and are very common in cesspools. Large numbers of adults 

 have been found to contain microfilariae {Filaria hancrofti), showing both thoracic 

 and proboscis infections. Experimentally these mosquitos are difficult to feed in 

 captivity, as they do not bite at all readily ; they feed better about an hour before 

 dawn. Larvae thrive and pupate in water to which 1% of common bar soap or 1% 

 human urine has been added. 



Culex tigripes, Grp. A considerable number of these useful larvae have 

 been taken throughout the town in association with C. fatigairis, S. fasciata and 

 A. costalis, They are capable of destroying large numbers of mosquito larv^ae ; I have 

 seen two adult larvae destroy thirty Stegomyia larvae in an hour. Adults have never 

 been taken in houses, and in captivity will not feed on blood. In a mixed collection 

 of larvae C. tigripes can be easily detected by their almost Anopheline position in 

 the water and generally white colour. 



Eretmopodites quinquevittatus, Theo. Larvae are common in small dirty 

 collections of water, especially in empty Molluscan shells ; those of the land snail, 

 Achatina panthera, nearly always harbour a number of these larvae. Adults have 

 never been captured in houses, but are common in low bush and wooded areas. 

 I have never been able to induce adults to feed on human blood in captivity. They 

 partake greedily of banana and dates, and when fed on such a diet females have 

 been shown to lay fertile eggs. The eggs, which are of a dark brown colour, are laid 



