Preparation and laboratory evaluation of herbal stick formulations using mosquito repellent plant materials against Aedes aegypti and Aedes albopictus

Abstract

Dengue, caused by Aedes mosquitoes, remains a significant public health issue. Current vector control methods have been unable to effectively reduce the Aedes populations, thereby failing to control dengue transmission rates. This study has attempted to develop an effective and practical tool for the control of dengue transmission by dengue vectors, Aedes aegypti and Aedes albopictus by reducing vector population and human-vector contact using mosquito repellent plant materials. In the current study, to prepare the incense herbal sticks Ocimum Basilicum, Tagetes erecta, Mentha piperita, Syzygium aromaticum, Cinnamomum verum, Salvia rosmarinus, Laurus nobilis and Cymbopogon nardus were used as herbal materials while saw dust, charcoal powder and “Patta” powders were used as inactive ingredients. The final weight of the herbal stick was 1.5 g and three different herbal formulas were prepared. Adult mosquitoes were reared in the laboratory from eggs collected via ovitraps deployed in various locations. F1 generation of mosquitoes were used and, their age of exposure was 2 weeks. Ytube experiments (n = 21) were conducted to assess the repellent activity of incense sticks impregnated with different herbal extracts. Additionally, smoke toxicity tests were performed on adult female mosquitoes. Statistical analyses were conducted using JMP 5.01 (SAS Institute Inc., 2002). Data were initially tested for homogeneity of variances using O’Brien’s test (p < 0.05). For homogenous variances, ANOVA was applied; if variances were heteroscedastic, data transformation was attempted to rectify the issue. Persistent heteroscedasticity led to the use of Welch ANOVA. Significant treatment effects were further analyzed using the Tukey-Kramer HSD test (p < 0.05) to compare the mean values. Test results clearly indicated that all three treatments resulted in significant reductions in attraction of both A. aegypti (F2,6 = 10.23, p < 0.05); and A. albopictus (F2,6 = 13.07, p < 0.05). Among the three formulations, incense stick that contains 45 % of active ingredients acted as the best repellent to Aedes species. The smoke toxicity test results depicted that both Aedes species showed significant toxicity to three treatments i.e. 5%, 25% and 45%, p < 0.01). The highest mortality was obtained with 45% of active ingredients, followed by moderate toxicity at 25%, and the lowest mortality at 15%, demonstrating a dose-response relationship. Therefore, incense sticks that contain 45 % herbal ingredients could be recommended as supplementary method to reduce human-vector contact to both A. aegypti and A. albopictus mosquito species. For further improvement, long-term monitoring procedures should be established to evaluate the long-term effectiveness and user acceptability of these mosquito repellent formulations.