Biting rhythm, fecundity and longevity rate of Aedes albopictus (Skuse) females from different urbanized settings in Penang Island, Malaysia under uncontrolled laboratory conditions

Urbanization could potentially modify Aedes albopictus’ ecology by changing the dynamics of the species, and increasing the abundance of their breeding sites due to environmental changes, and thus contribute to dengue outbreaks. An efficient control of the vector requires a deeper understanding on the biological components of this vector. Thus, this study was conducted to evaluate the biting rhythm, fecundity and longevity rate of Ae. albopictus in relation to urbanization strata; urban, suburban and rural areas in Penang Island, Malaysia. The experiments were done in comparison to a laboratory strain. Twenty-four hours biting activity of all the mosquito strains showed a clear bimodal biting activity, with morning and evening twilight peaks. A two-way analysis of variance (ANOVA) found that there was statistically no significant interaction (F(69,192) = 1.337, P > 0.05) between the effects of biting time and mosquito strains. Meanwhile, fecundity rates were shown to be statistically significantly different between mosquito strains (F(3,442) = 10.559, P < 0.05) with urban areas having higher mean number of eggs (mean = 107.69, standard error = 3.98) than suburban (mean = 94.48, standard error = 5.18), and rural areas (mean = 72.52, standard error = 3.87). Longevity rates were significantly higher (F(3,441) = 31.259, P < 0.05) for mosquito strains from urban areas compared to the other strains. These findings would provide crucial and relevant fundamental information to the planning of control program in Malaysia, particularly Penang. Author Summary Aedes mosquito populations associated with human habitation in urban area do not only have the potential to cause biting nuisance, but also cause significant public health risks through the transmission of dengue virus. The socioeconomic effects of urbanization have been comprehensively studied by socio-ecologists, but the ecological effects and their impact on this vector biology was not known. The authors found that in Penang Island, the mean number of eggs laid per female of Aedes albopictus is high in the urban areas than those in suburban and rural areas. The survivorship is high for urban populations parallel to the fecundity rate and apparent biting pattern which is peak at dawn and dusk was noted for all Ae. albopictus strains. The changed environment in the urbanized area where more kinds of breeding containers and more blood sources produced by condensed human population supported by warm climate may facilitate larval development, enhance the vector survivorship and its reproductive fitness. These might be the reasons for quick adaptation and susceptibility of Ae. albopictus in urban areas. As higher fecundity rate and longer adult survival may enhance disease transmission, this species studied is indeed need high attention in terms of vector control.


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Aedes mosquito populations associated with human habitation in urban area do not 49 only have the potential to cause biting nuisance, but also cause significant public health risks 50 through the transmission of dengue virus. The socioeconomic effects of urbanization have 51 been comprehensively studied by socio-ecologists, but the ecological effects and their impact 52 on this vector biology was not known. The authors found that in Penang Island, the mean 53 number of eggs laid per female of Aedes albopictus is high in the urban areas than those in 54 suburban and rural areas. The survivorship is high for urban populations parallel to the 55 fecundity rate and apparent biting pattern which is peak at dawn and dusk was noted for all 56 Ae. albopictus strains. The changed environment in the urbanized area where more kinds of 57 breeding containers and more blood sources produced by condensed human population 58 supported by warm climate may facilitate larval development, enhance the vector 59 survivorship and its reproductive fitness. These might be the reasons for quick adaptation and 60 susceptibility of Ae. albopictus in urban areas. As higher fecundity rate and longer adult space, population density and the destruction of natural ecology [20]. The socioeconomic 72 effects of urbanization have been comprehensively studied by socio-ecologists [22,28,15]. 73 However, the ecological effects and their impact on vector biology and vector-borne 74 infectious disease transmission remain unclear.

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Most of the previous studies were concerned mainly on oviposition ecology from 76 larval habitats and abundance of Aedes species in various urbanized settings (13,20,29] The ovitrap sampling was conducted in three different areas which represent urban, 92 suburban and rural settings in Penang Island (Fig 1). The distance between each area is 93 approximately 21 km. Urban area is an area that is in a city without wooded areas containing a lot of 95 buildings and houses close to each other, high densities of human population, where people 96 often store water for domestic usage due to insufficient water supply (from indoor) (Rahman,97 2012). The urban location chosen for this study was Jelutong (5°23'15.9"N 100°18'29.2"E) 98 which is located at the Northeast Penang Island District. It is an urban area which contains 99 little vegetation with the land use types being primarily residential and commercial buildings 100 which are close to each other and public services.   In this study, Ae. albopictus were collected as larvae (fourth instar) and pupae from the 122 three study sites. A total of 30 ovitraps were deployed randomly at two meters apart 123 throughout the respective study areas at shaded sites to maximize the attractiveness of females 124 to oviposit [23]. Each of the ovitraps was filled with approximately 250 ml of chlorine-free 125 water and a paddle (10 cm x 2.5 x 0.3 cm) was placed as an oviposition substrate for the 126 mosquitoes to lay eggs. Five days later, samples from the ovitraps were placed into plastic 127 bottles and brought back to the insectary for rearing. Only larvae (fourth instar) and pupae 128 samples were transferred into paper cups as temporary containers containing water from the 129 7 ovitraps used and the top of the cup surface covered with nylon netting. The pupae were 130 reared until adult emergence. The eggs from the laboratory strain which were retrieved from 131 the VCRU were reared until adult emergence to be used in the experiment as well.

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Throughout this study, temperature and relative humidity in the insectary were 134 allowed to fluctuate with the weather outside which is an uncontrolled condition. Photoperiod 135 was also unregulated and changed with the surrounding environment. Windows were opened 136 and neither temperature controller nor air conditioner was used during this study.

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The mosquitoes were given access to a small cotton wool soaked in 10% sucrose solution on 145 the first day of their emergence and were replaced every two to three days in order to avoid 146 any fungal growth. The mosquitoes were allowed to freely mate for two days, and thereafter 147 starved for a brief period (12 h (Fig 2). Cotton wools were replaced every two to three days. A small 174 disposable plastic cup filled with 30 ml of chlorine-free water and lined with filter paper as an 175 oviposition substrate was placed in each cage to provide females with sites for egg deposition.    Whereas, for fecundity rate, the number of eggs produced per mosquito (dependent 207 variable) was used to compare between mosquito strains (independent variable) and were 208   The survival analysis shows distinct differences of the longevity rate of Ae. albopictus 280 females between four strains (urban, suburban, rural and laboratory strain). Referring to Fig 5,   281 females from the urban area showed the highest mean days of lifespan with 25.29 ± 1.10 than 282 those in suburban (23.12 ± 0.97), in rural (18.60 ± 1.14), and laboratory strain (11.89 ± 0.90).

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A log-rank test showed significant difference in the survival distributions for the four 284 different mosquito strains (X 2 = 72.28, d.f. = 3, P < 0.05).  [19], the nocturnal host-seeking activity positively correlated with the increasing light 309 intensity as Ae. albopictus is sensitive to dim light. In their study, they found out that the host- wherever the vector inhabits (urban, suburban or rural areas).

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The previous studies were concerned mainly on oviposition ecology and abundance of 321 species by urbanization [13,20,29]  showed how Aedes mosquitoes are better adapted to urban environment.

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The fecundity and longevity rate of laboratory strain mosquitoes was recorded as the