Insecticidal Property of Plumeria obtusa L. (Apocynaceae) Leaf Extracts Against Aedes aegypti (Diptera: Culicidae)

Mosquitoes are one of the most lethal animals in the world and transmit many dangerous human pathogens, causing millions of deaths each year. Aedes aegypti is generally known to be a vector of dengue, chikungunya and zika. Mosquito control is a major challenge nowadays when they became resistant against commonly available insecticides. To reduce this, it is important to look for alternative that are easily biodegradable. One such alternative could be bioactive products from phytochemicals by systematically exploring the global floral biodiversity. Therefore the present study was to evaluate the ovipositional deterrent activity of the ethanol, hexane leaf extracts of Plumeria obtusa against Aedes aegypti and also observe various types of sensilla located on the antennae, maxillary palp, tarsi and ovipositor of the Ae. aegypti using scanning electron microscope. The effect of ethanol and hexane leaf extracts of P. obtusa on oviposition of Ae. aegypti was determined under two sets of conditions (Choice and no choice oviposition assay). Among the total number of eggs laid 33.83% (ethanol), 38.15(hexane) was present in control medium when placed along with ovitraps with 0.1, 0.3, 0.7, 0.010 and 0.013% ethanol and hexane leaf extracts of P. obtusa in which appeared 27.88, 23.27, 11.79, 9.371 and 0.038 % (ethanol), 26.09, 18.14, 13.19, 4.357 and 0.042% (hexane) of eggs respectively. This was also indicated by ODI values (9.649, 18.48, 48.30, 82.86 and 99.77) (ethanol) and (18.76, 35.53, 48.59, 79.50 and 99.77) (hexane) (choice oviposition assay). Percent oviposition in 0.1, 0.3, 0.7, 0.010 and 0.013 % ethanol and hexane of leaf extracts of P. obtusa was 43.11, 28.77, 19.51, 3.875 and 0.090% (ethanol), 36.36, 26.21, 18.03, 8.888 and 0.181% (hexane) which were less compared to their control counterparts 56.88, 71.22, 80.48, 96.12 and 99.90 (ethanol), 63.63, 73.78 , 81.96 , 91.11 and 99.81 (hexane) respectively (no choice oviposition assay). The findings also revealed that both extracts (ethanol, hexane) showed promising ovipositional deterrent activity against adult Ae. aegypti.