Ovicidal and oviposition deterrence properties of Tabernaemontana divaricata (apocynaceae) against aedes albopictus and culex quinquefasciatus in Sri Lanka

Abstract

The global incidence of mosquito-borne infectious diseases has increased dramatically in recent decades due to the limitations of current vector mosquito control approaches. Plantbased insecticides are increasingly demanded to control vector mosquitoes, mainly because of their eco-friendly nature. In this study, the ovicidal and oviposition deterrent properties of Tabernaemontana divaricata (Crape Jasmine) leaf extracts were evaluated against two medically important vector mosquitoes: Aedes albopictus (dengue vector) and Culex quinquefasciatus (lymphatic filariasis vector). Bioactive components of the plant leaves were extracted using ethanol. Ovicidal bioassays were conducted to determine the lethal concentrations required to kill 50% and 90% (LC₅₀ and LC₉₀) of mosquito eggs. The oviposition deterrent activity of the plant was evaluated using 1% treatment solutions prepared by directly dissolving dried leaf powder in distilled water. The number of eggs laid in treatments and controls was recorded for seven days under field conditions. LC₅₀and LC ₉₀for Ae. albopictus were 626.6 ppm and 892.5 ppm, respectively. For Cx. quinquefasciatus, the respective values of LC₅₀and LC₉₀ were 553.2 ppm and 621.1 ppm. A strong positive correlation between egg mortality and the concentrations of treatment (Ae. albopictus r=0.993, p=0.001; Cx. quinquefasciatus, r=0.992, p=0.001) was observed. Deterrent properties were high during the first few days of the treatment (99.8% for Ae. albopictus and 100% for Cx. quinquefasciatus). A gradual reduction of the deterrent properties of the treatment was observed after the second day for Ae. albopictus and the fifth day for Cx. quinquefasciatus. The oviposition activity index (OAI) ranged from -0.97 to -0.12 for Ae. albopictus, while it was between -1 and -0.53 for Cx. quinquefasciatus. The results show that the leaf extracts of Ta. divaricata has great potential to be used as eco-friendly ovicides and oviposition deterrents against Ae. albopictus and Cx. quinquefasciatus mosquitoes.