Use of different coloured ovitraps in the surveillance of Aedes mosquitoes in an arid-urban area of western Rajasthan, India

Background & objectives: In the absence of any commercially available dengue vaccine or antiviral therapy, controlling the primary mosquito vector, Aedes aegypti, is currently the only means to prevent dengue outbreaks. Ovitraps are being employed as a sensitive method for detecting the presence of Ae. aegypti. Size, colour, material, paddle and use of oviposition attractant have been reported as important factors influencing the efficacy of ovitraps. Methods: For the study of coloured ovitraps baited with grass infusion, 24 households were randomly selected in a locality and five ovitraps/premises were installed. Weekly ovitrap surveys were conducted during the study for four times. Ovitrap data were analyzed on the basis of its location, day-wise percent positivity, presence of eggs laid and inference of different ovitrap parameters were drawn. Results: Grass infusion, used in the ovitraps has highest attractiveness on Day 6 in comparison to other days. Percent positivity of different coloured ovitraps revealed that red coloured ovitraps have highest positivity (92.7%), followed by black and orange (91.7% each), green (76.3%) and transparent (45.8%). The individual colour-wise ovitrap positivity revealed that the highest ovitrap positivity on Day 1 was recorded for black colour (21.8%), which on D2 and D3, in case of red colour (37.5 and 26%). However, on D4, D5 and D6 highest number of positive ovitraps was recorded in orange coloured (12.5, 21.9 and 31.3%, respectively) and on D7 highest number of positive ovitraps were recorded in transparent (21.9%), followed by green coloured ovitrap (20.8%). The overall location-wise ovitraps positivity revealed that highest positivity was recorded among the ovitraps installed inside bathrooms (92.0%), followed by bedrooms (85.0%), lobby (66.7%) and stores (48.3%). Interpretation & conclusion: The study revealed that for immediate detection of the presence of gravid females in a particular locality during epidemics, the black coloured ovitraps may be useful, however, in normal situations for surveillance of the vector species, the orange coloured ovitraps might be more suitable. Bathrooms were found to be the highest positive location for pitching ovitraps