Target and non-target activities of Thymus serpyllum essential oil, nanoemulsion, and thymol as ecofriendly sustainable tools for controlling Culex quinquefasciatus , the main vector of lymphatic filariasis

There is an urgent need to seek effective, ecofriendly, and sustainable pesticides to control mosquitoes due to the rising threats of conventional mosquitocide overuse and vector-borne diseases. To achieve this, essential oil (EO) was hydrodistilled from wild thyme, Thymus serpyllum (TsEO), and profiled using GC-MS and GC-FID. Forty-nine components, amounting to 98.64%, were identified where thymol was predominant (63.84%). A stable oil/water nanoemulsion (average size 37.1 ± 2.3 nm) was produced using a green protocol and characterized. The EO (TsEO), nanoemulsion (Ts-ONE), and thymol demonstrated remarkable larvicidal, adulticidal, and repellent activities against Culex quinquefasciatus Say. Superior bioactivities were observed with Ts-ONE. The 24 h larval LC50s were 10.4 µl/L, 17.2 µl/L, and 23.9 µl/L for Ts-ONE, TsEO, and thymol, respectively. Meanwhile, LC50s against adults ranged between 9.9 and 21.5 µl/L. The lethal time (LT50) ranged between 2.1 and 3.6 h against larvae and between 0.82 and 3.3 h against adults. Botanicals significantly repelled adults at 0.45–3.6 µL/cm2 and substantially inhibited larval AChE activity (IC50s ranged between 10.08 and 25.34 mg/L). They were relatively safe for Gambusia affinis and Diplonychus indicus, two aquatic larvivorous species. Results recommend the use of T. serpyllum EO, nanoemulsion, and thymol as green mosquitocides against Cx quinquefasciatus.