Comparative mosquitocidal and repellence activities of essential oil, nanoemulsion and main terpenes of <i>Deverra tortuosa</i> against <i>Aedes albopictus</i> with insights into the non-target effects

There is an urgent and renewed interest in searching for effective and green pesticides to control mosquitoes. In this framework, the essential oil (EO) of the plant <i>Deverra tortuosa</i> was hydrodistilled, and analysed using gas chromatography-flame ionisation detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Dillapiole (40.2%), elemicin (8.1%), and myristicin (6.3%), phenylpropanoids, and sabinene (4.3%) a common monoterpene, were found to be the major EO components. The oil nanoemulsion (ONE) was developed adopting a green protocol, and then characterised. The EO, ONE, and terpenes, particularly the phenylpropanoids possessed considerable mosquitocidal bioactivity against the Asian tiger mosquito, <i>Aedes albopictus</i>. A percentage of 100% larval mortality was recorded when insects were treated with a concentration of 40 μL/mL of ONE after 24 hours of treatment, while double of this concentration from EO and dillapiole was required to achieve the same activity. The LC₅₀’s against larvae ranged between 7.6 and 60.7 μL/mL. For adults, LC₅₀’s ranged between 6.4 and 50.9 μL/L. At sub-lethal concentrations (0.625-5.0 μL/cm²), EO materials significantly repelled <i>Ae. albopictus</i>, where a concentration of 5.0 μL/cm2 of EO and ONE provided 100% protection for up to180 min. As a proposed mechanism of action, the EO materials considerably inhibited the activity of acetylcholinesterase (AChE). The test materials were safe for the mosquitofish, <i>Gambusia affinis</i>, a common larvivorous fish, and <i>Eisenia fetida</i> earthworm. Test materials were also safe for the white albino rat in an oral bioassay at a limit dosage of 3500 mg/kg b.wt. The findings support the use of the EO, nanoemulsion, and phenylpropanoids of <i>D. tortuosa</i> as environmentally benign natural mosquitocodes to control <i>Ae. albopictus</i>.