High efficacy of (Z)-γ-Bisabolene from the essential oil of Galinsoga parviflora (Asteraceae) as larvicide and oviposition deterrent against six mosquito vectors

The eco-friendly control of mosquitoes with novel and effective larvicides and oviposition deterrents is a crucial challenge to prevent outbreaks of mosquito-borne diseases. However, most of the herbal formulations tested in these years showed LC50 values higher of 10 ppm, and oviposition deterrent activity only when tested at relatively higher doses (>50 µg/ml). Here, we focused on the chemical composition of the essential oil (EO) of Galinsoga parviflora, an annual herb native to South America and naturalized all over the world, testing its larvicidal and oviposition deterrent action against 6 mosquito species. Totally 37 compounds were identified in the EO of G. parviflora by GC and GC-MS analyses. The major constituent was (Z)-γ-bisabolene (38.9%). The G. parviflora EO and (Z)-γ-bisabolene showed acute toxicity on An. stephensi (LC50=31.04 and 2.04 µg/ml), Ae. aegypti (LC50=34.22 and 2.26 µg/ml), Cx. quinquefasciatus (LC50=37.10 and 2.47 µg/ml), An. subpictus (LC50=40.97 and 4.09µg/ml), Ae. albopictus (LC50=45.55 and 4.50µg/ml) and Cx. tritaeniorhynchus (LC50=49.56 and 4.87 µg/ml) larvae. Furthermore, the oviposition deterrent potential of the G. parviflora EO and (Z)-γ-bisabolene was studied on six mosquito vectors, showing that 25 µg/ml of (Z)-γ-bisabolene led to Oviposition Activity Index lower of -0.79 in all tested mosquito vectors. Overall, all larvicidal LC50 values estimated for (Z)-γ-bisabolene were lower than 5 µg/ml, this result far encompass current evidences of toxicity reported for the large majority of botanical products currently tested against mosquito young instars, allowing us to propose this compound as mosquito larvicide and oviposition deterrent.