Monitoring the post-exposure effectiveness of a new herbal incense stick formulation against Aedes aegypti and Aedes albopictus

Abstract

Aedes mosquitoes have a high prevalence and are responsible for the transmission of dengue fever among humans. The objective of this study was to develop a herbal incense stick (HS) formulation using mosquito-repellent plant materials and investigate the effectiveness, if any, of the HSs in reducing the population of vector mosquitoes. The effectiveness of the HSs was evaluated by monitoring their impact on the fecundity, egg hatchability, pupation, and adult emergence of Aedes aegypti and Aedes albopictus. HSs were prepared mixing extracts of Ocimum basilicum, Tagetes erecta, Mentha piperita, Syzygium aromaticum, Cinnamomum verum, Salvia rosmarinus, Laurus nobilis, Cymbopogon nardus with inactive matrix material, namely, charcoal, “patta”, and sawdust. Three different herbal formulations were created making the final weight of an HS as 1.5 g. Mosquito eggs were collected using ovitraps. Twenty-five unfed adult female mosquitoes per species were exposed for 3 minutes in a glass chamber of 8000 cm3. Their mortality was recorded 24 hours later. The surviving females were blood-fed for 2 days. They were allowed to mate with unexposed healthy males. Gravid females were isolated to measure fecundity. After 5 days, the eggs were hatched (24±2℃, 70±10% RH) to determine their hatchability. The larvae were then reared and fed until pupation and adult emergence. Counts were recorded at each stage of observation. ANOVA, Welch ANOVA, and Tukey-Kramer HSD tests were conducted. Results of the study revealed a significant effect of HS on the fecundity of the mosquitoes (F3,8=610.13, P<0.01), and on the hatchability of eggs (F3,8=1899, P<0.01). Transformation of larvae into pupae and pupae into adults showed no significant difference between the treatments. HS containing 45% herbal ingredients demonstrated the highest post-exposure effectiveness. The tested formulation of HS has proven to be an effective tool for reducing human-vector contact and inhibiting the development of both embryonic and post-embryonic stages of the relevant mosquito species.