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R. B. JACKSON
flaps and collects such mosquitoes as are imprisoned between the nets with the help of a flashlight. In a room in a house close to Anopheline breeding places catching was done for 27 nights, the average catch per night worked out at 2 Anophelines.
In the same locality day catching between the hours of 9.30 a.m, and 12.30 p.m. for 67 days averaged 10 per day or 3 per hour, which were nearly all A. minimus. Dissections of Anophelines mosquitoes caught in January, February, and March revealed no infections. In April there was 1 infection out of 139 dissected, in May none, in June 3 out of 304, in July 46 out of 517. All these were A. minimus. In July the sporozoite rate was 5%. Now if 2 A. minimus can be caught in a bedroom every night during July, 62 would have been caught, and of these 62, 3 would have had sporozoites in their salivary glands and so be capable of infection whoever they bit, so that the chances of persons not protected by nets getting malaria during the months of high mosquito infection is by no means slight. Culicine biting pests have their uses by making people use mosquito nets which they are inclined to dispense with if only a few non-obtrusive Anophelines are present which are not very noticeable. The obtaining of Anophelines in quantity for dis- sections in this part of the world has not so far been found an easy task: those of A. minimus forming the great majority in both day and night catches.
If the blood of persons suffering from filarial infection is taken late in the evening or at night and examined under the microscope it is often found swarming with little worms. If a mosquito feeds on such a person these worms find their way into the insect's stomach and from thence to the muscles of its thorax, and undergo development there if the mosquito is a suitable host: from the thoracic muscles the worms make their way through the neck into the head and finally come to rest in the proboscis. When the mosquito proceeds to bite a victim, the sheath opens and the worms make their way through the end of it on to the skin and pass through the skin into the body where they attain sexual maturity. The female gives rise to numer- ous embryos which find their way into the blood and can be demonstrated there as already mentioned.
The worms in the mosquito are known as larval filaria, the adult worm in the human body as filaria and the worm in the blood as microfilaria. In some parts of the world filarial infection gives rise to Elephantiasis, in other parts, enlarged glands are a prominent feature, in others affections of the genitals. There is a disease called heart worm in dogs which, I under- stand, occurs in the Island. A mosquito said to be Culex fatigans is the vehicle by which this filarial infection is carried from one dog to another in a similar fashion to the human infection. Sir Patrick Manson discovered other species of filaria-Filaria corvi-torquati in the white necked crow and Filaria pecemedia in a magpie: so when one finds larval filarial infection in a Culicine or Anopheline mosquito it does not always follow that the in- fection is derived from human sources. A. minimus has been found in- fected with larval filaria to the extent of 3.5% in an area where 13 out of 106 persons harboured microfilaria in their blood. Up to date five A. minimus have been met with infected both with malaria, and larval filaria.
A Brief Account of Mosquitoes
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Epidemics of Dengue take place from time to time in Hong Kong.
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In many parts of the world Aedes argenteus is considered to be the carrier. The infection cannot be demonstrated in the mosquito by means if a microscope as in the case of malarial infection or filarial infection. This mosquito is the great carrier of yellow fever. In Hong Kong I have seldom encountered this insect which is a small black and white mosquito with a lyre. shaped device on the back of its thorax, but Aedes albopictus which closely resembles it, is very common. Aedes albopictus has a single white stripe on the back of the chest. It has been experimentally infected with dengue in the Philippines, and mosquitoes infected in Java by feeding on dengue patients have been kept alive and sent to Amsterdam where they infected volunteers in that city.
The Hong Kong Naturalist.
December 1932.
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