Influence of Cassia occidentalis leaf and stem extracts on the life parameters of Aedes aegypti (Linnaeus, 1762)

Mosquitoes are the most common disease vectors for several prevalent diseases, such as Dengue, Zika, Malaria, Encephalitis, Chikungunya, and yellow fever. Since the last few years, the world has recorded an unprecedented rise in Aedes-borne dengue incidences. Frequent use of chemicals has resulted in hazardous effects on the environment, non-targets and humans, necessitating the need to develop a safer and more efficient control strategy using plant-based products. The present study investigated the effects of Cassia occidentalis on various biological parameters of the Aedes aegypti larvae. The hexane extracts obtained from the leaf and stem of the plant were utilized to treat the larvae for 24 hours. The LC50 values for the leaf and stem extracts of C. occidentalis were determined as 0.103 mg/mL and 0.088 mg/mL, respectively. The corresponding lethal values of leaf and stem extracts obtained against pupae were 0.111 and 0.138 mg/mL. The extracts also imparted latent toxic effects and reduced the % adults developed from the survived larvae in the 60.00-61.67% range at the median lethal dose. The extract-treated larvae were restless and showed abnormal behaviour, like aggressive movements and self-biting of anal papillae. The inner membrane cuticle of anal papillae was shrunken and the gut region was damaged and disintegrated. The adults who emerged from the larvae, treated with 1.0 mg/mL of C. occidentalis hexane stem and leaf extracts, showed 1.8-fold and 2.29-fold decreased oviposition, respectively. Further study with identified bioactive constituents in the extracts can help to formulate green insecticides for Ae. aegypti management.