INSECTS AND DISEASE 



409 



Anopheles have been found to convey one or other of the 

 three Protozoa causing human malaria (see Fig. 68). Only 

 the female mosquito bites man. Through the extensive 

 distribution of these mosquitoes malaria has become the 

 most widespread of all diseases. Anopheles macultpennts , 

 which occurs all over Europe, A. funestus and A. gamhice 

 in Africa, A. culicifacies and A. fuliginosus in India, and 

 A. ludlowi in Malaysia, are well-known malaria carriers. 

 Various species of Culex, a related genus, carry Plas- 

 modium prcecox, which causes malaria in birds. C fatigans 

 and C. pipiens, amongst others, spread the nematode 

 worm Filaria bancrofti {F. nocturna), which causes 

 filariasis in man. In a person suffering from this 

 disease the blood vessels of the skin swarm by night with 

 larval filariae, which during the day retire to the deeper 

 vessels of the body. Manson has pointed out that this is 

 probably an adaptation to the night-flying habits of the 

 mosquitoes, within which the next stage in the life-history 

 of the parasite is passed. When such a mosquito sucks 

 the blood of an infected person, the larval filariae pass from 

 the mosquito's stomach to the thoracic muscles, where they 

 develop. Thence they migrate to the region of the mouth 

 to await being liberated on to the skin of a new host, and 

 boring into it. They then migrate to the lymphatics and 

 soon mature. 



A mosquito, Aedes argenteus {Stegomyia fasciata)^ which 

 occurs in all parts of the world between the parallels 40° 

 N. and S., is the proved carrier of the, as yet, unknown 

 parasite of yellow fever. " It is a most vicious biter both 

 by day and night, and breeds in small artificial collections of 

 water, such as barrels, puddles, cisterns, and even in such 

 small receptacles as sardine tins " (Theobald). Aedes and 

 othermosquitoesalsotransmitDengufe Fever (Australia, etc.). 



Control measures are based on knowledge of the life- 

 history and habits of the mosquito. The eggs are laid 

 on or near water. Hence drainage to destroy breeding- 

 places is of first-rate importance. Covering the surface of 

 ponds, etc., with a thin film of oil kills off the newly 

 hatched larvae and pupae, which cannot breathe through 

 the oil. Where oil cannot be used, pools or tanks may be 

 stocked with certain fish known to feed on mosquito larvae. 



