Landing periodicity of Aedes aegypti with implications for dengue transmission in Trinidad, West Indies

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1 158 Journal of Vector Ecology December, 2000 Landing periodicity of Aedes aegypti with implications for dengue transmission in Trinidad, West Indies Dave D. Chadee and Raymond Martinez Insect Vector Control Division, Ministry of Health, 3 Queen Street, St. Joseph, Trinidad and 9 Gaston Johnston Street, St. James, Port of Spain, Trinidad, West Indies Received 5 Jan 2000; Accepted 15 May 2000 ABSTRACT: The diel landing/biting periodicity of the Trinidad strain of Aedes aegypti (L.) was monitored using human-bait during January-August Hourly light intensities were measured both indoors and outdoors at both urban and rural sites. The periodicity of females was diurnal and nocturnal, with 90% arriving during daylight and twilight and 10% during the night. The pattern of landing was trimodal, with consistent peaks at 0700h, 1100h and 1700h. The diel periodicities at indoor and outdoor urban sites were virtually identical. In contrast, the periodicities in rural areas differed, with no nocturnal activities being recorded at indoor and outdoor sites. At both urban and rural sites, larger numbers of adults were collected outside than inside houses. A significant correlation between light intensities and mosquito landing patterns was observed. The implications of the changing landing patterns of Ae. aegypti within urban areas are discussed in light of the epidemiology and control of dengue fever in Trinidad.Journal of Vector Ecology 25(2): Keyword Index: Aedes aegypti, landing/biting cycle, dengue, light regimen, epidemiology and control. INTRODUCTION The recent emergence and re-emergence of dengue fever and its hemorrhagic manifestations within the Caribbean region can be attributed to numerous anthropological factors including demographic and societal changes (Monath 1994, Gubler and Kuno 1997), post World War II increases in air-and seatransportation (Monath 1994, Gubler and Kuno 1997), and failure of Aedes aegypti programs due to a lack of political will (Rosenbaum et al. 1995, Gubler and Kuno 1997). The dengue pandemic within the Caribbean region has been attributed to numerous biological factors including the development of insecticide resistance in the vector Ae. aegypti (Rawlins 1998, Vaughan et al. 1998), the longer feeding times required for dengueinfected mosquitoes (Platt et al. 1997), changes in physical size and geographical origin of mosquito strains that enhanced their vector potential (Sumanochitrapon et al. 1998), and the introduction of different dengue strains or serotypes within the Caribbean region (Rico-Hesse 1990, Gubler and Kuno 1997). Behavioral studies show varying patterns in biting times of Ae. aegypti according to locality and also to the form or subspecies studied (Lumsden 1957, McClelland 1959, 1960, Teesdale 1955, Boorman 1960, Atmosoedjono et al. 1972, Trpis et al. 1973, Corbet and Smith 1974 and Chadee 1988). Most studies show a characteristic diurnal landing pattern in Africa (van Someran et al. 1958, McClelland 1960, Boorman 1960, Trpis et al. 1973) and within the Americas (Chadee 1988) but some night-time feeding of Ae. aegypti has been reported in captive and wild populations in Africa (Macfie 1915, Teesdale 1955, Lumsden 1957). Corbet and Smith (1974) reported a trimodal periodicity of landing of Ae. aegypti in Tanzania with peaks at h, h and h, while Atmosoedjono et al. (1972) working in Indonesia also reported a trimodal pattern of landing, with peaks at h, h and h. In both studies the mid-morning peak was interpreted as either due to a sampling error (Corbet and Smith 1974) or a reflection of seasonal changes (Atmosoedjono et al. 1972). During the course of investigating dengue cases in Trinidad, two interesting and important observations were made on the landing behavior of Ae. aegypti. This involved a mid-morning peak in landing (similar to Atmosoedjono et al and Corbet and Smith 1974), as well as night-time landing activity by Ae. aegypti females at indoor and outdoor sites in Trinidad. These patterns were different to that described for the Trinidad strain of Ae. aegypti by Chadee (1988). Therefore, based on these preliminary observations, a pilot study

2 December, 2000 Journal of Vector Ecology 159 was conducted using human-bait collections, to reexamine the landing periodicity of Ae. aegypti females at urban and rural sites in Trinidad. MATERIALS AND METHODS This study was conducted during January-August 1999 at Woodbrook (10 o 41 N; 61 o 33 W), representing an urban site of approximately 200ha, 5000 people and 1000 houses, within the suburban area of the capital city of Port of Spain, and Tableland (10 o 17 N; 61 o 17 W) representing a rural community of approximately 100 ha, 2000 people and 500 houses, 31km east of San Fernando, the industrial capital of Trinidad. Human bait captures were conducted according to the procedures outlined by Haddow (1954). Collections were made one day each week between 0400 and 2400 hours in two houses, with one man sitting on the porch (outside) and another sitting in the living room. Mosquito collectors worked a 10 h shift in the morning and afternoon. Mosquitoes were caught with hand nets or aspirators from the catcher s lower legs and ankles and transferred into moistened plaster of Paris lined jars. After each hour, a new collection jar was used. The jars containing mosquitoes were labeled giving location, time of collecting, date and name of collector. These jars were then stored on ice and subsequently transported to the Insect Vector Control Division laboratory, St. Joseph, Trinidad where they were identified. While mosquitoes were being collected, light intensities were simultaneously measured each hour at both indoor and outdoor sites and at both urban and rural locations using a standard Weston Master II photographic light meter (Model 753) facing directly upwards (incident light) and directly downwards (reflected light) at the center of the collection room. The mean reading was then calculated and recorded in foot candles. RESULTS A total of 1239 Ae. aegypti females was collected at the two sites, with 49.1% (278 indoors and 330 outdoors) in the urban area and 50.9 % (279 indoors and 352 outdoors) in the rural area (Table 1). Figure 1 shows the trimodal patterns of landing of the domestic strain of Ae. aegypti mosquitoes at indoor and outdoor sites in both urban Port of Spain and rural Tableland, Trinidad. Within the urban area, the diel landing periodicity of Ae. aegypti was predominantly diurnal (90%) but with a small nocturnal component (10%). In contrast, in the rural area the landing periodicity was predominantly diurnal with no significant nocturnal activity (Figure 1). Females were collected during every daylight hour. In both the urban and rural areas the overall pattern was trimodal and similar with distinct peaks 1 hour after sunrise, 1 hour before noon and 1 hour before sunset. Light measurements at both indoor and outdoor locations in Tableland and Woodbrook are shown in Figure 2. The light intensity measurements at both the urban and rural sites were similar during the periods 0500 to 1800 hours. However, from 1900 to 0100 hours, significantly (G=45.9 d.f. 12, P>0.01) lower intensities were measured at both indoor and outdoor Table 1. Summary of collections of Aedes aegypti females landing on human bait at indoor and outdoor sites, in urban (Woodbrook) and rural (Tableland) Trinidad, West Indies (January-July, 1999). Sites No. of females collected % % % % URBAN SITE Indoors Outdoors Sub-total RURAL SITE Indoors Outdoors Sub-total Total

3 160 Journal of Vector Ecology December, 2000 Figure 1. Diel landing periodicity of Aedes aegypti at indoor (A) and outdoor (B) urban sites in Woodbrook and at indoor (C) and outdoor (D) rural sites in Tableland, Trinidad, West Indies. The number of females landing is expressed as percent.

4 December, 2000 Journal of Vector Ecology 161 Figure 2. Indoor (solid line) and Outdoor (dotted line) light intensity measurements (foot candles) at urban Woodbrook (A) and rural Tableland (B) sites in Trinidad, West Indies. sites in the urban and rural areas (Figure. 2). DISCUSSION The results of this study demonstrate that the diel landing periodicity of the Trinidad strain of Ae. aegypti is both diurnal and nocturnal (Figure 1). At both indoor and outdoor sites, the diel landing was tri-modal with peak landing occurring during the same three hours each day, with the peaks in the early morning and late afternoon being larger than that observed at midmorning. Similar peaks in landing were observed at rural and urban indoor and outdoor sites in Trinidad (Fig.1) These findings suggest that the trimodal patterns previously found by Atmosoedjono et al. (1972) in Indonesia and by Corbet and Smith (1974) in Tanzania were real and not due to sampling error, seasonal differences or geographical variations as suggested by those authors. However, in an earlier study using the same Trinidad strain of Ae. aegypti, Chadee (1988) observed a predominately diurnal landing pattern with only two peaks, one between and the other at hours. These results suggest that Ae. aegypti may have modified its landing activity at indoor and outdoor sites at both urban and rural areas. Chadee (1988) reported a slightly extended landing period at indoor sites during h but no landing adults were observed after 2000 h. It is noteworthy that Chadee and Corbet (1990) also found oviposition occurrences between h and suggested it may have resulted from increased activity in homes and recommended that further studies were required. Here we provide additional data required to support that original inference and also to extend it. The collection of Ae. aegypti during nocturnal hours ( h) is new for the Trinidad strain but this feature is known to occur in Africa, where it is often confined to the 2 h following sunset (Macfie 1915, Teesdale 1955, Lumsden 1957, Van Someen et al. 1958; McClelland, 1959, 1960). The night-feeding component observed at only the urban sites may have significant epidemiological consequences because it extends the period during which dengue transmission can occur. This extended window of opportunity for human-vector contact culminates at times of peak human activity as reported by Chadee (1988). That is, at late evening and at night when householders are usually casually dressed with more surface area of the human body exposed and accessible to landing Ae. aegypti mosquitoes. Therefore, the number of female Ae. aegypti per person (whether small or large in number) can increase transmission by multiple feeding (a feature well recognized by Macdonald 1956, Scott et al. 1993)

5 162 Journal of Vector Ecology December, 2000 during these opportune periods of human presence and possible inactivity (e.g watching television, computing or having dinner) and longer feeding hours. These factors may well explain the increase in the occurrence of clusters of dengue patients in the same household with similar dates of onset of illness (Morrison et al. 1998), the rapid and often explosive spread of dengue (Rodriguez-Figueroa et al. 1995) and the low prevalence of dengue in rural populations (Hayes et al. 1996). In addition, the extension of the landing periodicity of Ae. aegypti during nocturnal hours may have occurred as an adaptation to light, that is, the effect of an increase in electrical lighting in and around houses may have had a similar effect to that observed among forest mosquitoes during moonlight. For example, Anopheles bellator Dyar and Knab shifted its peak landing periodicity from to hours during moonlight (Chadee 1992). It is noteworthy that at both urban and rural sites most landing Ae. aegypti were collected when light intensities ranged from 15 to 25 foot candles and this suggests that internal and external lighting may influence the landing pattern of this vector species. Therefore, the increase in street lighting, use of dusk to dawn external security lighting and use of other internal light fittings in houses may have increased light intensities that mimic conditions similar to daylight/twilight within homes, thereby providing suitable conditions to extend the hours of landing activity by Ae. aegypti in urban environments. However, during the present study nocturnal activity was not observed in the rural area which was generally darker than the urban area, with minimal or no street lighting, only essential internal light fittings in houses and extensive shade and shadows cast by large trees (Figure 2). Consequently, due to the high intensity of light observed in some urban areas it is difficult to follow the strict definition of day and night due to the amount of artificial light measured during night-time. Mosquitoes found within cities and major townships in Trinidad and elsewhere may well modify or adapt their behavior to changing light regimens. Acknowledgements We thank Dr Joan M. Sutherland, Department of Biological Sciences, Dundee University for the initial observations and suggestion to conduct this study. We also thank Messrs Lester James, F. Mohammed, S. Deonarine and J Alfonso, Insect Vector Control Division for assistance in the field. This paper is published with permission of the Ministry of Health, Trinidad, West Indies. REFERENCES CITED Atmosoedjono, S., P.F.D. van Peenan, R. See and J.S. Soroso Man-biting activity of Aedes aegypti in Djakarta, Indonesia. Mosq. News 32: Boorman, J.P.T Studies on the biting habits of the mosquito, Aedes (Stegomyia) aegypti Linn., in a West African village. W. Afr. Med. J. 9: Chadee, D.D Landing periodicity of the mosquito Aedes aegypti in Trinidad in relation to the timing of insecticidal space-spraying. Med. Vet. Entomol. 2: Chadee, D.D Effects of moonlight on the landing activity of Anopheles bellator Dyar and Knab (Diptera: Culicidae) in Trinidad, West Indies. Bull. Soc. Vect. Ecol. 17: Chadee, D.D. and P.S. Corbet Diel patterns of oviposition indoors of the mosquito, Aedes aegypti (L.) (Diptera: Culicidae) in Trinidad, W.I.: a preliminary study. Ann. Trop. Med. Parasitol. 84: Corbet, P.S. and S.M. Smith Diel periodicities of landing of nulliparous and parous Aedes aegypti (L.) at Dar es Salaam, Tanzania (Diptera: Culicidae). Bull. Entomol. Res. 64: Gubler, D.J. and G. Kuno Dengue and Dengue Haemorrhagic Fever. CAB International, Oxon, UK. 478 pp. Haddow, A.J Studies of the biting-habits of African mosquitoes. An appraisal of methods employed, with special reference to the twenty four hour catch. Bull. Entomol. Res. 45: Hayes, C.G., I.A. Phillips, J.D. Callahan, W.F. Griebernow, K.C. Hyams, S. Jue-Wu, and D.M. Watts The epidemiology of dengue virus infection among urban, jungle, and rural populations in the Amazon region of Peru. Am. J. Trop. Med. Hyg. 55: Lumsden,W.H.R The activity cycle of domestic Aedes (Stegomyia) aegypti (L.) (Diptera Culicidae) in Southern Province, Tanganyika. Bull. Entomol. Res. 48: Macdonald, W.W Aedes aegypti in Malaysia. II. Larval and adult biology. Ann. Trop. Med. Parasitol. 50: Macfie, J.W.S Observations on the bionomics of Stegomyia fasciata. Bull. Entomol. Res. 6: McClelland, G.A.H Observations on the mosquito Aedes (Stegomyia) aegypti (L.) in East

6 December, 2000 Journal of Vector Ecology 163 Africa. I. The biting cycle in an outdoor population at Entebbe, Uganda. Bull. Entomol. Res. 50: McClelland, G.A.H Observations on the mosquito Aedes (Stegomyia) aegypti (L.) in East Africa. II. The biting cycle in a domestic population on the Kenya coast. Bull. Entomol. Res. 51: Monath, T.P Dengue: the risk to developed and developing countries. Proc. Natl. Acad. Sci. USA 91: Morrison, A.C., A. Getis, M. Santiago, J.G. Rigua-Perez, and P. Reiter Exploratory space-time analysis of reported dengue cases during an outbreak in Florida, Puerto Rico, Am. J. Trop. Med. Hyg. 58: Platt, K. B., K. J. Linthicum, K. S. Myint, B. L. Innis, K. Lerdthusnee and D. W. Vaughn Impact of dengue virus infection on feeding behavior of Aedes aegypti. Am. J. Trop. Med. Hyg. 57: Rawlins, S.C Spatial distribution of insecticide resistance in Caribbean populations of Aedes aegypti and its significance. Pan Am. J. Publ. Hlth. 4: Rico-Hesse, R Molecular evolution and distribution of dengue viruses type 1 and 2 in nature. Virology 174: Rodriguez-Figueroa, L., J. Rigau-Parez, E.L. Suarez, and P. Reiter Risk factors for dengue infection during an outbreak in Yanes, Puerto Rico in Am. J. Trop. Med. Hyg. 52: Rosenbaum, J., M.B. Nathan, R. Ragoonanansingh, S.C.Rawlins, C.Gayle, D.D.Chadee and L.S. Lloyd Community participation in Dengue prevention and control: a survey of knowledge, attitudes and practice in Trinidad and Tobago. Am. J. Trop. Med. Hyg. 53: Scott, T.W., C.G. Clark, L.H. Lorenz, P. Amersinghe, P. Reiter and J.D. Edman Detection of multiple blood feeding in Aedes aegypti (Diptera; Culicidae) during a single gonotrophic cycle using a histological technique. J. Med. Entomol. 30: Sumanochitrapon, W., D. Strickman, R. Sithiprasasna, P. Kittayapong and B.L. Ennis Effect of size and geographic origin of Aedes aegypti on oral infection with dengue -2- virus. Am. J. Trop. Med. Hyg. 58: Teesdale, C Studies on the bionomics of Aedes aegypti (L.) in its natural habitats in a coastal region of Kenya. Bull. Entomol. Res. 46: Trpis, M., G.A.H McClelland, J.D.Gillett, C. Teesdale and T.R. Rao Diel periodicity in the landing of Aedes aegypti on man. Bull. Wld. Hlth. Org. 48: Van Someren, E.E.C., R.B. Heisch, and M. Furlong Observations on the behavior of some mosquitoes of the Kenyan coast. Bull. Entomol. Res. 49: Vaughan, A., D.D. Chadee, and R. ffrench-constant Biochemical monitoring of organophosphorus and carbamate insecticide resistance in Aedes aegypti mosquitoes in Trinidad. Med. Vet. Entomol. 12:

Further Evaluation of Indoor Resting Boxes for Aedes aegypti Surveillance

Further Evaluation of Indoor Resting Boxes for Aedes aegypti Surveillance By Pattamaporn Kittayapong Department of Biology, Faculty of Science, Mahidol University, Bangkok, Thailand Kenneth J. Linthicum