INTRODUCTION
Dengue is one of the most serious vector-borne dis- eases of public health importance in the world. It is caused by four serotypes of dengue virus (DEN 1–4) in India.
Aedes aegypti is the principal vector of dengue in India with recent reports of Ae. albopictus also transmitting dengue viruses1–2. According to an estimate, about 40%
of the world’s population is at risk of infection with den- gue viruses3. Dengue is prevalent throughout India af- fecting most of the metropolitan cities and towns. During the year 2014, 40,571 cases of dengue with 137 deaths were reported from India4.
The biology of mosquito vectors is influenced by sev- eral factors of which temperature is one of the key fac- tors. Effect of temperature on larval biology has been studied in different mosquito species including Ae.
aegypti5–7. Temperature for rearing of mosquito larvae
influences body size, fecundity and longevity of emerg- ing adult mosquitoes8–10. Developmental time of larvae is also influenced by the temperature resulting in faster development at higher temperatures while slow develop- ment at lower temperatures11.
Ae. aegypti is container breeder mosquito preferring intradomestic and peridomestic containers such as tank, cooler, cistern, bird pot, tyre, water storage jar, plastic cup etc12. All these containers are made up of different materi- als, i.e. plastic, iron, rubber, earthen material etc. The tem- perature of water in different containers is likely to vary depending upon the materials of the container. A signifi- cant variation between environment and water-container temperatures has been reported earlier13. While studying the effect of temperature on development of Ae. aegypti in Australia, Tun-Lin et al6 found that the position of water containers kept in different places in field and larval food resources in nature affected larval developmental period
Impact of container material on the development of Aedes aegypti larvae at different temperatures
Gaurav Kumar
1, R.K. Singh
1, Veena Pande
2& R.C. Dhiman
11National Institute of Malaria Research (ICMR), New Delhi; 2Department of Biotechnology, Kumaun University, Nainital, Uttarakhand, India
ABSTRACT
Background & objectives: Aedes aegypti, the primary vector of dengue generally breeds in intradomestic and peridomestic containers made up of different materials, i.e. plastic, iron, rubber, earthen material etc. The material of container is likely to affect the temperature of water in container with variation in environmental temperature.
The present study was aimed to determine the effect of different container materials on larval development of Ae.
aegypti at different temperatures.
Methods: Newly hatched I instar larvae (2–4 h old) were used in the study and experiments were conducted using three different containers made up of plastic, iron and earthen material. Three replicates for each type of container at 22, 26, 30, 34, 38, 40, and 42°C were placed in environmental chamber for the development of larvae.
Results: At temperatures >22°C, 50% pupation was completed in earthen pot within 4.3±0.6 to 6.3±0.6 days followed by plastic containers (5±0 to 8±0 days) and iron containers (6±0 to 9±0 days). Developmental time for 50% pupation in the three containers differed significantly (p < 0.05) at all the experimental temperature ranges.
A significant variation was found in the temperature of environmental chamber and the temperature of water in three types of containers (p < 0.05). The difference in the temperatures of water in different containers resulted in significant variations in the developmental period of larvae. More than 35°C temperature of water was found inimical for pupal development.
Interpretation & conclusion: The results revealed the variation in temperature of water in different types of containers depending on the material of container, affecting duration of larval development. As the larval development was faster in earthen pot as compared to plastic and iron containers, community should be discouraged for storing the water in earthen pots. However, in view of containers of different materials used by the community in different temperature zones in the country, further studies are required for devising area-specific preventive measures for Aedes breeding.
Key words Aedes aegypti; container material; environmental temperature; larval development; water temperature
Eggs of Ae. aegypti were obtained from the insectary of the National Institute of Malaria Research, New Delhi on moist filter paper strips. The egg strips were placed in porcelain tray containing one litre of water and allowed to hatch for 24 – 48 h. Newly hatched I instar larvae (2–
4 h old) were used in the study. Experiments were con- ducted using three different containers made up of plas- tic, iron and earthen material. The 500 ml of tap water kept for 24 h was added to each of the containers and 50 I instar larvae were pipetted into them. Three replicates for each type of container at 22, 26, 30, 34, 38, 40, and 42°C were placed in environmental chamber (Kaleido- scope Climatic Solutions, Bengaluru). Water temperature in each container was measured using portable digital thermometer every day at 1100 hrs. Larval food compris- ing of dog biscuits and fish food (60 : 40) was provided for larval feeding. The larval development in different containers was monitored after every 24 h and checked for mortality, if any. At the same time water and food in the containers was also changed. The difference in devel- opmental time from larva to pupa was analysed by single factor ANOVA. Mortality rate and difference of tempera- ture in water containers and environmental chamber was analysed by two factor ANOVA. All the statistical analy- ses were done with the help of MS-Excel 2007.
pupation did not differ significantly among different types of containers at different temperatures except at 26°C (p <0.05). In earthen pots, 50% pupation was achieved faster (4.3 ± 0.6 days) as compared to the plastic (5 ± 0 days) and iron containers (6 ± 0 days) at 34°C. At tem- peratures >22°C, 50% pupation in earthen pots was com- pleted within 4.3 ± 0.6 to 6.3 ± 0.6 days whereas in iron containers it took 6 ± 0 to 9 ± 0 days and 5 ± 0 to 8 ± 0 days in plastic containers. Duration of 50% pupation in the three containers differed significantly (p <0.05) at all the selected temperature ranges. At 22°C the larvae took longest time to pupate (12.7 ± 0.6 to 15.7 ± 0.6 days) while shortest time in pupation was at 34°C (6 ± 0 to 7 ± 0 days) in all the containers. Except at 38°C, the differ- ence in pupation time was significant (<0.05) among the three containers at all the selected temperature range . Out of the three containers, pupation did not occur in the iron containers at 38°C while at 40°C there was no pupa- tion in any of the three types of containers. Larval devel- opment period at different temperatures was averaged for each of the containers, which was found shortest (6.4 days) in case of earthen pots followed by plastic containers (7.2 days) and iron containers (8.3 days) (Fig. 1)
A significant variation was found between the temperature of water in three types of containers and the temperature of environmental chamber (p < 0.05). The
Table 1. Impact of container material on development of Aedes aegypti larvae at different temperatures
Temperature of Day of commencement p-value Day of 50% pupation p-value Day of cessation p-value
environmental of pupation (Mean±SD) (Mean±SD) of pupation (Mean±SD)
chamber (°C) Plastic Iron Earthen Plastic Iron Earthen Plastic Iron Earthen
container container pot container container pot container container pot
22 10.3±0.6 9.7±0.6 9.3±0.6 0.177 12.3±0.6 11±1 10.3 ±0.6 0.042 15.7 ±0.6 12.7±0.6 13.7 ± 0.6 0.001
26 7.3±0.6 7.3±0.6 5.6±0.6 0.018 8±0 9±0 6.3 ±0.6 0.0 9 ±0 10±1 7.6 ± 0.6 0.014
30 5±0 5±0 4.6±0.6 0.421 5±0 6.3±0.6 5 ±0 0.003 6.3 ±0.6 8±0 6.6 ± 0.6 0.010
34 4.7±0.6 5.3±0.6 4.3±0.6 0.177 5±0 6±0 4.3 ±0.6 0.002 6 ±0 7±0 6.3 ± 0.6 0.027
38 5.6±0.6 NP 5±0 0.11 6±0 NP 5 ±0 0.0 8.3 ±0.6 NP 9 ± 0 0.116
40 NP NP NP NP NP NP – NP NP NP –
SD—Standard deviation; NP—No pupation.
DISCUSSION
In this study temperature of water in the different types of containers was found lower than the temperature of environmental chamber. The observed difference was highest in case of earthen pots (1.9–4.1°C) and least in iron containers (0.8–2.5°C) which may be due to the dif- ference in thermal conductivity of these materials. Iron has the thermal conductivity of 80 W/mK making it most conductive while the earthen pots have a thermal con- ductivity of <1 W/mK making it a thermally insulated material14. Thus, the water was found warmer in iron con- tainers in comparison to that in plastic and earthen pots.
The difference in the temperature of water in different types of containers resulted in the significant variations in the larval developmental period. Variation between temperature of water in iron and plastic containers was
< 1°C. It was lower than reported in an earlier study con- ducted in Australia where variation of 3.6°C temperature was found between plastic and metal containers resulting in faster development (6 days) from larva to adult in metal containers6. The temperature of water in contain- ers has been found to vary with the exposure of the containers with sunlight in one of the study conducted in Texas15.
In the present study the optimum temperature of wa- ter for larval development was found to be ranging from 23.6 to 32.2°C as delayed development was observed at 35°C in all the containers. Larval development was ar- rested leading to 100% larval mortality beyond this tem- perature. As per the results of the study, at temperature
>32.2°C, Ae. aegypti larvae experienced stress due to in- crease in temperature that might have caused abnormali- ties at the cellular level in larvae16. Higher temperature causes faster growth resulting in less nutrient reserves
Fig. 1:Impact of container material on Ae. aegypti larval development from larva to pupa.
Table 2. Observed variation in water temperature of different containers with respect to environmental temperature Temperature of Temperature of water in environmental different containers (°C)
chamber (°C) Plastic Iron Earthen
containers containers pots
22 20.8 21.2 20.1
26 24.2 24.8 23.6
28 25.9 26.5 25.5
30 27.6 28.3 27.2
34 31.3 32.2 31
38 35 35.9 34.3
40 36.7 37.7 35.9
42 38.7 39.5 37.9
temperature of water in all the containers was found lower than the temperature of environmental chamber (Table 2). The difference in temperature between water and environmental chamber was highest in case of earthen pots (1.9–4.1°C) followed by plastic (1.2–3.3°C) and iron containers (0.8–2.5°C). The difference of environmental and water temperature was positively correlated with the rise in temperature of environmental chamber.
Mortality rate of Ae. aegypti larvae in different con- tainers is shown in Fig. 2. At 38°C temperature, the lar- val mortality in earthen pots, plastic and iron containers was found 43.3, 50 and 100% respectively. At 40°C, 100%
mortality was observed in all types of containers. Over- all, lowest mortality rate was recorded in the earthen pots except at 22°C temperature. Mortality rate differed sig- nificantly (p < 0.01) among different types of containers and across all temperature treatments. Two way interac- tions between temperature and container materials were also significant for mortality rate (p <0.01).
Fig. 2:Impact of container material on larval mortality of Ae. aegypti at different temperatures.
undertaken with constant temperature in environmental chamber, while the earlier study was conducted in field conditions with diurnal variation of temperature in water storage drums.
In one of the study undertaken recently in Delhi, Singh et al20 reported that water filled earthen pots kept for birds are the second most preferred breeding habitats for Aedes mosquitoes. Similar observations were also made by Kumari et al1; and Das and Hazra21. Use of earthen pots may serve as very potent container for the breeding of Ae. aegypti due to faster development of larvae. There- fore, to reduce larval habitats for Aedes breeding, the use of earthen pots should be discouraged. In Delhi and other states of India, it is a common practice to store water in drums and containers made up of plastic. These contain- ers are one of the major sources of Aedes breeding. If iron containers are used instead of plastic particularly during summers when temperature reaches >34°C, de- velopment of Aedes larvae will be hampered resulting in lower density of Aedes mosquito.
CONCLUSION
This study underscores the importance of container material as breeding ground for in developmental time and survival of larvae of Aedes aegypti . The results pro- vide evidence of the variation in temperature of water experienced by mosquito larvae in different types of con- tainers depending on the material of container. As the development of Ae. aegypti was found more conducive in earthen pots as compared to plastic and iron contain- ers, community should be discouraged to store water in earthen pots. Keeping in view, the variety of containers used in different temperature zones of the country, fur- ther studies may be undertaken with other container ma- terials for better understanding of Aedes larval develop- ment in nature and to adopt better control strategies.
ACKNOWLEDGEMENTS
The authors are thankful to the Director, National
sion of dengue virus in Aedes albopictus (Diptera: Culicidae) in Kerala, a southern Indian state. Jpn J Infect Dis 2007; 60(5):
245–9.
3. Farrar J, Focks D, Gubler D, Barrera R, Guzman MG, Simmons C, et al. Towards a global dengue research agenda. Trop Med Int Health 2007; 12(6): 695–9.
4. Dengue/DHF situation in India. Delhi: National Vector Borne Disease Control Programme (NVBDCP), Directorate General of Health Services, Ministry of Health & Family Welfare 2016.
Available from: http://nvbdcp.gov.in/den-cd.html (Accessed on May 26, 2016).
5. Bar-Zeev M. The effect of temperature on the growth rate and survival of the immature stages of Aedes aegypti (L.). Bull Entomol Res 1958; 49: 157–63.
6. Tun-Lin W, Burkot TR, Kay BH. Effects of temperature and larval diet on development rates and survival of the dengue vec- tor Aedes aegypti in north Queensland, Australia. Med Vet Entomol 2000; 14: 31–7.
7. Mohammed A, Chadee DD. Effects of different temperature regi- mens on the development of Aedes aegypti (L.) (Diptera: Culi- cidae) mosquitoes. Acta Trop 2011; 119(1): 38–43.
8. Briegel H. Metabolic relationship between female body size, re- serves, and fecundity of Aedes aegypti. J Insect Physiol 1990;
36: 165–72.
9. Briegel H, Timmermann SE. Aedes albopictus (Diptera: Culi- cidae): Physiological aspects of development and reproduction.
J Med Entomol 2001; 38(4): 566–71.
10. Oda T, Eshita Y, Uchida K, Mine M, Kurokawa K, Ogawa Y, et al. Reproductive activity and survival of Culex pipiens pallens and Culex quinquefasciatus (Diptera: Culicidae) in Ja- pan at high temperature. J Med Entomol 2002; 39: 185–90.
11. Rueda LM, Patel KJ, Axtell RC, Stinner RE. Temperature-de- pendent development and survival rates of Culex quinquefaciatus and Aedes aegypti (Diptera: Culicidae). J Med Entomol 1990;
27(5): 892–8.
12. Samuel PP , Thenmozhi V, Nagaraj J, Kumar TD, Tyagi BK.
Dengue vectors prevalence and the related risk factors involved in the transmission of dengue in Thiruvananthapuram district, Kerala, south India. J Vector Borne Dis 2014; 51(4): 313–9 13. Townroe S, Callaghan A. British container breeding mosquitoes:
The impact of urbanisation and climate change on community composition and phenology. PLoS One 2014; 9(4): e95325. doi:
10.1371/journal.pone.0095325.
14. Thermal conductivity of some common materials and gases.
Available from: http://www.engineeringtoolbox.com/thermal- conductivity-d_429.html (Accessed on February 16, 2016).
15. Clayton JB. Effects of storage container color and shading on water temperature. M.Sc. Thesis. Texas, USA: Texas A & M University 2011; p. 1–30.
16. Clements AN. The biology of mosquitoes, v I. Development, nu-
Correspondence to: Dr R.C. Dhiman, Scientist ‘G’, National Institute of Malaria Research (ICMR), Sector 8, Dwarka, New Delhi–110 077, India.
E-mail: [email protected]
Received: 24 February 2016 Accepted in revised form: 25 March 2016 trition and reproduction. London: Chapman Hall 1992; p. 509.
17. Bayoh MN, Lindsay SW. Temperature-related duration of aquatic stages of the afrotropical malaria vector mosquito Anopheles gambiae in the laboratory. Med Vet Entomol 2004; 18(2): 174–9.
18. Denlinger DL, Yocum GD. Physiology of heat sensitivity.
In: Hallman GJ, Denlinger DL, editors. Temperature sensitivity in insects and application in integrated pest management.
Boulder: Westview Press 1998; p. 7–57.
19. Hemme RR, Tank JL, Chadee DD, Severson DW. Environmental
conditions in water storage drums and influences on Aedes aegypti in Trinidad, West Indies. Acta Trop 2009; 112(1): 59–66.
20. Singh RK, Mittal PK, Kumar G, Dhiman RC. Prevalence of Aedes mosquitoes in various localities of Delhi during dengue trans- mission season. Entomol Appl Sci Lett 2014; 1(4): 16–21.
21. Das B, Hazra RK. Entomological investigations with special at- tention to pupal indicators of Aedes vectors during outbreaks of dengue in coastal Odisha, India. J Vector Borne Dis 2013; 50(2):
147–50.
