Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City

Bull. Org. mond. Sant '1971, 4, 629-633Bull. Wid Hlthi Org.J Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City 2. Larval Habitats * K. L. CHAN,' B. C. HO 2 & Y. C. CHAN3 Detailed information on the breeding habitats of Ae. aegypti and Ae. albopictus is necessary when planning programmes for their control. The larval habitats of the two species in 10 city areas were counted and classified according to type, frequency of occur- rence, location, and function. Of all the breeding habitats recorded 95 % were domestic containers. The most common Ae. aegypti breeding habitats were ant traps, earthenware jars, bowls, tanks, tin cans, and drums, ant traps being the most common indoors and earthen- ware jars the most common out doors. Breeding habitats for Ae. albopictus were com- monly found in earthen ware jars, tin cans, ant traps, rubber tires, bowls, and drums; ant traps were the most common indoor habitat and tin cans were most common outdoors. The majority of Ae. aegypti breeding habitats were found indoors, while only half of all the Ae. albopictus breeding habitats were indoors. The indoor and outdoor distribution ofbreeding habitats ofboth species was not related to the type ofhousing in the area. The distribution of the type of breeding habitats, however, was related to the type of housing in the area. Ant traps were common to all areas, but water-storage containers and unused containers were common in slum-house and shop-house areas. Flats, however, had more containers usedfor keeping plants andflowers. The most common breeding habitats of Ae. aegypti and Ae. albopictus are discussed in relation to the habits of the people. It is concluded that control of the two species will depend largely on a change in such habits, either through public health education or by some form of law enforcement. Much is known of the breeding habitats of Aedes aegypti. The breeding habitats of Aedes albopictus have been less well studied but most reports record this species as breeding primarily in natural habitats such as tree holes and bamboo stumps. In South- East Asian countries, this species is also known to be well established in artificial containers such as jars, tin cans, and bottles in and around human dwellings. For the control or eradication of Ae. aegypti and * This study was supported in part by a grant from the Rockefeller Foundation, New York, to the Department of Bacteriology, University of Singapore. Requests for reprints should be addressed to Dr Y. C. Chan, Department of Bacteriology, University of Singapore, Sepoy Lines, Singa- pore'3. 1 ChiefVector Control Officer, Vector Control & Research Branch, Ministry of Health, Singapore. ' Lecturer, Department of Parasitology, University of Singapore, Singapore. ' Lecturer, Department of Bacteriology, University of Singapore, Singapore. Ae. albopictus, exhaustive information on the breeding habitats is important. In addition to the major breeding habitats the minor ones must also be recognized as reinfestation can occur from them. Few such studies have been made, except in Honolulu, Hawaii (Bonnet, 1947), Guam (Hull, 1952), and Malaysia (Cheong, 1967). In the first paper of this series we showed that both Ae. aegypti and Ae. albopictus commonly breed in and around houses in Singapore City. This paper describes the larval habitats of the two species. STUDY AREAS Information on the larval habitats of Ae. aegypti and Ae. albopictus was obtained from surveys carried out between 1966 and 1968 in 10 city areas. The areas and the different types of housing have already been described (Chan, Chan & Ho, 1971). 266 -629- 4 630 K. L. CHAN, B. C. HO & Y. C. CHAN Table 1. Number of different types of breeding habitat METHODS of Ae. aegypti or Ae. albopictus in Singapore city A breeding habitat is defined here as one in which Type of habitat No. Percentage larvae or pupae, or both, are present at the time of I___________ _ _ of total inspection. A potential habitat is one containing Natural habitats: water but no larvae or pupae at the time of inspec- Earth drains, pits, trenches 28 tion. The habitats were not examined for the presence of eggs. Definitions of other terms may beCoconut shells 6 found in the previous paper (Chan, Chan & Ho, Vehicle tracks 5 1971). Leaf axils 4 All breeding and potential habitats were examined Mollusc shells 4 and counted, except for dumps of scrap metal and Ground pools 2 rubber tires where the number of habitats was0.6 estimated from a random sample of 10 habitats from each dump. Such dumps were very few and were not Domestic habitats: found in all the areas studied. Ant traps 2 050 All the larvae and pupae (collectively called larvae Earthenware jars 1 533 in this paper) found in breeding habitats, except Bowls 830 large ones such as drums, earthenware jars, and Tin cans 705 rubber tires, were collected, identified, and counted. Tanks 613 Only a few random collections were made from large containers. Drums 497 Pots 286 RESULTS Bottles 258 Types ofbreeding habitat Plates 166 Table 1 lists the types of habitat in which larvae of Vases 165 either Ae. aegypti or Ae. albopictus, or both, were Basins 164 found. The breeding habitats have been classified Pails 125 into 6 categories: (1) natural, (2) domestic, (3) rubber Cups 114 tires, (4) water and sewage-disposal installations, Barrels 46 (5) building equipment and parts of machinery, and(6) boats. Breeding of both species occurred in aPans 22 great variety of habitats but the largest number of Dishes 20 habitats belonged to the domestic category. The Others (total of 13 types) 204 domestic containers were those directly associated 94.6 with the household and were used for such purposes Rubber tires 291 3.5 as water storage, ornamentation (e.g., flower vases and flower pots), or the prevention of pests (e.g., Water and sewage disposal ant traps). They constituted 95% of the total breed-installations: ing habitats of the two Aedes species in the urban Drains 52 parts of Singapore. Others a 20 0.9 Common breeding habitats Building equipment and machi- Altogether 6 915 Ae. aegypti breeding habitats and nery parts b 29 0.4 1 872 Ae. albopictus breeding habitats were found (Table 2). The 6 most common Ae. aegypti breeding Boats 3 habitats were ant traps, earthenware jars, bowls, tanks, tin cans, and drums, in that order. Ant traps Total 8 242 100.0 accounted for 28 % of the total breeding habitats of this species and were the most common breeding a Water-pipes, manholes, sewage tanks, stop-cock pits, sumps, habitat found indoors, while earthenware jars were gb Cement-mixers, concrete blocks, scrap iron, etc. the most common outdoor breeding habitat (Table 3). AE. AEGYPTI AND AE. ALBOPICTUS IN SINGAPORE. 2 631 Table 2. Common breeding habitats of Ae. aegypti Table 3. Percentage distribution of the most common and Ae. albopictus and their percentage distribution Aedes breeding habitats indoors and outdoors Habitat Ae. aegypti Ae. albopictus Ae. aegypti Ae. albopictus abitatI Habitat Indoors Outdoors Indoors Outdoors Ant traps 27.8 12.8 Earthenware jars 19.4 16.5 Ant traps 35.1 2.8 30.5 1.1 Bowls 10.8 6.6 Earthenware jars 16.5 29.0 13.5 18.5 Tanks 8.3 3.3 Bowls 12.6 4.7 13.8 1.9 Tin cans 7.0 15.9 Tanks 8.8 6.6 3.1 3.4 Drums 6.2 5.8 Drums 5.0 10.2 3.6 7.2 Pots 3.4 3.5 Tin cans 4.2 16.2 8.2 20.9 Bottles 2.7 4.7 Rubber tires 0.8 7.2 1.5 15.4 Rubber tires 2.3 9.9 Others a 17.0 23.3 25.8 31.6 Vases 2.1 1.7 Total number of habi- Basins 1.9 2.5 tats with larvae 5 335 1 580 740 1 132 Plates 1.8 2.8 .1 Pails 1.3 2.6 a Including 23 different types. Others a 5.0 11.4 Total number of Table 4. Percentage of breeding habitats indoor habitats with larvae 6 915 1 872 in different areas Percentage of breeding a Including 17 different items. Housing habitats indoors AAreaegypt,Ae. albo-Ae. aegypti pictus Earthenware jars, tin cans, ant traps, rubber tires, bowls, and drums were the 6 most common breeding Chinatown Shop house 75.5 51.8 habitats of Ae. albopictus. Ant traps were also the Roh Shop house 82.1 54.9 most common indoor breeding habitat of the species, while tin cans were the most common out- Henderson Slum house 58.2 32.6 door breeding habitat (Table 3). Geylang West Slum house 75.9 55.3 Tiong Bahru Flat 86.1 83.8 Distribution of breeding habitats indoors and outdoors Al da| Flat 86.1 3.8Alexandra Flat 92.9 39.7 Of all Ae. aegypti breeding habitats, 78% were found indoors, whereas 50% of Ae. albopictus breed- All areas All types 78.1 49.8 ing habitats were indoors (Table 4). There were differences in the distribution of breeding habitats in the different areas according to the predominant . . type of housing. In general, areas with fats had the D uction highest percentage of Ae. aegypti breeding habitats function indoors while slum-house areas had the lowest The distribution and usage of the various breeding percentage. Ae. albopictus breeding habitats showed habitats in the slum-house, shop-house, and flat wider differences in their distribution even in areas areas are shown in Table 5. Ant traps were common with a predominantly similar type of housing. In the in all three areas although they were used to a two slum-house areas, for instance, the proportion of lesser extent in shop houses. Shop houses in China- breeding habitats indoors was 33% and 55 %; town are generally occupied by more than one family similarly, of the two areas with flats, one had 40% and the overcrowding in the kitchen makes it while the other 84% of the breeding habitats necessary for some families to hang their meat safes indoors. from the ceiling, obviating the need for ant traps. 632 K. L. CHAN, B. C. HO & Y. C. CHAN Table 5. Distribution of Aedes breeding habitats according to usage in three areas Usage of the following types of container Area and housing type Total no. of Ant-traps Water storage Ornamental Junk No. % No. % No. % No.| % Henderson (Slum houses) 436 132 30.3 133 30.5 18 4.1 153 35.1 Tanjong Pagar (Shop houses) 373 81 21.7 118 31.6 62 16.6 112 30.0 Alexandra (Flats) 379 144 38.0 29 7.7 137 36.1 69 18.2 Total 1 188 357 30.1 280 23.6 [217 18.3 334 128.1 It is also possible that at the time of survey many of containers for water storage because not every house the ant traps in Chinatown were dry and were has a piped water supply. Shop houses usually do not therefore not classified as breeding habitats. have enough taps to supply all the families living in Water-storage containers (earthenware jars, tanks, each house. Flats, on the other hand, are usually and drums) were more common in the slum-house and occupied by only one family and water containers shop-house areas than in flats. Slum houses require are found in them less frequently. Flower vases and flower pots were common in Table 6. Number of actual and potential breeding flats but were seldom found in slum houses. On the habitats for Aedes in Singapore city other hand empty tin cans, bottles, and other unused containers were abundant in slum-house areas but No. of habitats were less frequently found in the areas with flats. _ _ _ _ 1 ~~~Breeding Potential ToaType of habitat _-_ _-_Brn a TPotential breeding habitats Earthenware jars 1 533 16 949 18 482 In addition to the survey of breeding habitats, the number of potential habitats was enumerated, as far as possible, to determine the relative abundance of Tanks 613 4 546 5 159 each type of habitat in the city areas. The two most Bottles 258 4 244 4 502 common habitats (breeding and potential) utilized by Tin cans 705 3 179 3 884 the two Aedes species were ant traps and jars Bowls 830 2 425 3 255 (Table 6). Drums 497 2 607 3 104 DISCUSSION Rubber tires 291 797 1 088 Our study has confirmed that both Ae. aegypti and Vases 165 593 758 Ae. albopictus in urban areas breed in a great Pots 286 433 719 variety of habitats. Measures for the control or Pails 125 463 588 eradication of these two species can be effective onlyif information on their breeding habitats is available.Cups 114 374 488 In most control programmes, it is necessary only to Basins 164 221 385 reduce the mosquito population to below the Plates 166 146 312 disease-transmission level, which could be achieved Barrels 46 116 162 by removal of only the most common breeding Pans 22 24 46 habitats. For purposes of eradication, however, it is Dishes 20 6 26 necessary to destroy also the minor breeding habitatsso that reinfestation from these sources is not Others (27types) 357 92 449 possible. In Singapore City, 99% of the breeding habitats of Total 8 242 49 385 57 627 the two species were of the artificial type. Natural habitats, such as earth drains, coconut shells, and AE. AEGYPTI AND AE. ALBOPICTUS IN SINGAPORE. 2 633 leaf axils, comprised only 0.6% of the total breeding habitats. Of the artificial habitats, domestic con- tainers were predominant (95%), and the ones in which breeding was most commonly found were ant traps, earthenware jars, bowls, tanks, tin cans, and rubber tires. Thus the most common breeding habitats of Ae. aegypti and Ae. albopictus in Singapore are closely associated with the habits of the people. Control of these mosquitos will depend largely on a change in such habits, either through public health educa- tion or by some form of law enforcement. ACKNOWLEDGEMENTS The authors thank the Deputy Director of Medical Services, Ministry of Health, for pennission to publish this paper. They also acknowledge the valuable assistance of the staff of the Vector Control and Research Branch, especially Miss Tay Siew Khuan, Mr Gan Sing Hai, and Mr Teo Boo Teck. RtSUMt AEDES AEGYPTI (L.) ET AEDES ALBOPICTUS (SKUSE) DANS LA VILLE DE SINGAPOUR: 2. GtTES LARVAIRES Les gites larvaires d'Aedes aegypti et d'A. albopictus decouverts dans 10 secteurs de la ville de Singapour ont t6 etudies et classes d'apres leur type, leur frequence, leur emplacement et l'usage auquel ils 6taient primitive- ment destines. Ces gites, a la fois naturels et artificiels, offraient une tres grande variet6, mais les recipients a usage domestique repr6sentaient 95% d'entre eux. Parmi les principaux gites utilises par A. aegypti figuraient les pieges a fourmis, les jarres en terre cuite, les cuvettes, les reservoirs, les boites de conserve et les tonneaux; les pieges 'a fourmis fournissaient les gites de predilection a l'interieur des maisons, et les jarres a l'ext6rieur. A. albopictus s'installait particulierement dans les jarres, les boites de conserve, les pieges a fourmis, les pneus, les cuvettes et les tonneaux; sa pref6rence se portait sur les pieges a fourmis as l'interieur et sur les boites de conserve en dehors des locaux. Les gites situes a l'interieur des habitations represen- taient 78% de tous les gites d'A. aegypti et 50% de ceux d'A. albopictus. La r6partition des gites des deux esp6ces a l'interieur ou 'a l'exterieur n'etait pas fonction du genre d'habitation, mais ce dernier influengait en revanche la repartition par type des gites. Si les pieges a fourmis etaient partout nombreux, on rencontrait des recipients servant au stockage de l'eau ou non utilises surtout dans les bas quartiers et dans les centres commerciaux, tandis que dans les quartiers residentiels on trouvait de nom- breux recipients contenant des plantes ou des fleurs. Ce sont en definitive les pieges a fourmis et les jarres qui se sont rev61s les plus propices a l'installation de gites des deux especes d'Aedes dans tous les secteurs. Les auteurs examinent pour terminer les caracteris- tiques de chacun des gites les plus courants en relation avec les habitudes des habitants. Ils concluent que le succes de la lutte contre Aedes est en grande partie tri- butaire d'une modification de ces habitudes, profonde- ment enracinees, par la coercition ou par l'education sanitaire. REFERENCES Bonnet, D. D. (1947) Proc. Hawaii ent. Soc., 13, 43-49 Chan, Y. C., Chan, K. L. & Ho, B. C. (1971) Bull. Wld Hlth Org., 44, 617-627 Cheong, W. H. (1967) Bull. Wld Hith Org., 36, 586- 589 Hull, N. B. (1952) U.S. ArmedForces med. J., 3, 1287-1295