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REPORT REGARDING THE MOSQUITOES THAT OCCUR IN THE
COLONY OF HONGKONG.
HONGKONG, 15th February, 190%.
SIR—I have the honour to submit, for purposes of the Annual Medical Report, the results of a systematic examination and classification of the mosquitoes that prevail in Hongkong and its Dependencies, on which I was engaged during the twelve months ending 30th September, 1901.
For some months previous to September, 1900, I was working at the subject as I had opportunity, but my field of observation was limited to the Colony itself until in that month the Honourable F. H. MAY, C.M.G., Captain Superintendent of Police, kindly consented to my proposal that I should be supplied with at least one dozen mosquitoes from each of the Police Stations throughout Hongkong itself and the New Territory once a week for a year. As the Police Stations are approximately equally scattered over the whole area, the mosquitoes that were sent to me may be assumed to fairly satisfactorily represent the actual relative prevalence of these insects in this locality.
2. I distributed a number of glass test-tubes to each of the thirty-six Police Stations, with general instructions for the catching and transmitting of the insects in such a way as to avoid injury to them. They were to be caught by means of the glass tubes, killed by a whiff of tobacco-smoke, and sent enclosed in match-boxes to the Central Police Station, from which they would be duly forwarded to me. It was requested that about two-thirds of each consignment should be caught in the evening, or from mosquito-curtains in the early morning, and the remainder from species seen flying about in the day time; and further that no selection of any kind should be made, the first dozen or so caught on any given date being sent.
The arrangements made have been carefully carried out by the officers in charge of the stations, with few exceptions; and I beg to express my thanks to the Captain Superintendent of Police, Chief Inspector MACKI, and the officers of the Police Force for their hearty co-operation in this research.
3. During the twelve months, 1st October, 1900, to 30th September, 1901, 32,266 insects were sent to me from the Police Stations. Of these, 31,390 proved to be mosquitoes; the others were chiefly insects belonging to cognate families, such as fungus gnats (Mycetophilidae), midges (Chironomidæ), sand flies (Simulidæ), &c.
1,169, or 3.7 per cent. were Anopheles, of three species, and 30,221, i.e., 96.3 per cent. were Culex, of twelve species. As is shown in Appendix II, the number of species of Culex is probably considerably larger, some that I describe as varieties being perhaps distinct species.
4. I enclose a Table (Appendix I) showing in detail my observations during the year as regards the various Police Stations. I show for each station the number of specimens received, the number of Anopheles and Culex respectively, and the names of the species of both that have come from the station. I describe the different species by letters corresponding to those used in the Systematic Account of Hongkong Mosquitoes given below (Appendix II). Similar tables showing the same facts, but without the names of species, for each month and each quarter of the year are included in my quarterly reports on this subject, which have appeared in the Government Gazette.
5. The monthly percentage of Anopheles and Culex has been as follows:-
...
6. In considering the percentage of Anopheles in the foregoing table, two modifying circumstances require to be allowed for. The percentage for October, 1900, is too high, owing to the fact that I was then receiving an unduly large number of insects from the more malarial Police Stations, and less in proportion from the more healthy stations. And on the other hand, the percentage of Anopheles shown for August and September, 1901, is probably much below the average for the Colony as a whole during those months, owing to the fact that from the end of June vigorous measures for the destruction of the larva and breeding-places of these insects were in operation in the neighbourhood of all my collecting stations. I drew up a series of simple instructions on this subject, as brief and elementary as possible, and these were embodied in a General Order to officers in charge of Police Stations by the Captain Superintendent of Police (cf. Appendix III). They were carried into effect more or less thoroughly, and, while the Police reaped the benefit, my statistics were vitiated in the direction I have indicated. Allowing for these modifying circumstances, it will be found that the prevalence of the Anopheles mosquito runs quite parallel with what we already know of the prevalence of malaria in the Colony. Both are at their minimum in February, and at their maximum between the months of July and October.
7. No Anopheles were found among mosquitoes sent to me from the following stations:-
No. 5, No. 7, No. 8, Kennedy Town, Mount Gough, Shaukiwan, Tsim Sha Tsui, Stone Cutters' Island, Hung Hom, and Kat O.
8. The following Table shows the stations from which Anopheles were sent to me, and the percentage of Anopheles among the total mosquitoes received from those stations:-
Station Mosquitoes examined Anopheles Culex Aberdeen 1,261 6 (0.5%) 1,255 (99.5%) Stanley 575 1 (0.2%) 574 (99.8%) Shek O 1,178 1 (0.1%) 1,177 (99.9%)9. In Appendix II I describe systematically the mosquitoes that prevail in the Colony, examining in each case the wings, legs, head, appendages, thorax, abdomen, and size. The size I express in millimetres (inch). It will be noted that, so far as Hongkong is concerned, the wings of Anopheles are in all species spotted, and those of all forms of Culex unspotted.
There are three species of Anopheles—a sub-species of Anopheles Sinensis, and two species which have been recognised as new species, not thus far observed elsewhere, by Mr. F. V. THEOBALD, Entomologist at the British Museum, to whom I submitted them. He has named one of them Anopheles Maculatus from its markings, the other Anopheles Minimus from its minute size. The former I at first believed to correspond to Anopheles Costalis of West and South Africa, but there are specific differences. I need not here enter into descriptive details, which I have set forth at length in the Appendix.
Anopheles Sinensis breeds chiefly in the rice-fields and the ditches surrounding or draining them, the other two chiefly in the ravines; but they do not confine themselves exclusively to their usual habitats.
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