(1) Background: Mosquito control with essential oils is a growing demand. This work
evaluated the novel larvicidal and adulticidal activity of fennel and green tea oils and their Layered
double hydroxides (LDHs) nanohybrid against Culex pipiens (Cx. pipiens) in both laboratory and
field conditions and evaluated their effect against non-target organisms; (2) Methods: Two types of
nanoclays, MgAl-LDH and NiAl-LDH were synthesized and characterized using PXRD, TEM and
SEM, whereas their elemental analysis was accomplished by SEM-EDX; (3) Results: Mg and Ni LDHs
were synthesized by the co-precipitation method. The adsorption and desorption of active ingredients
were conducted using LC MS/MS, with reference to the SEM-EXD analysis. The desorption process
of MgAl-LDH intercalated green tea oil was conducted using ethanol, and reveled significant peaks
related to polyphenols and flavonoids like Vanillin, Catechin, Daidzein, Ellagic acid, Naringenin,
Myricetin and Syringic acid with concentrations of 0.76, 0.73, 0.67, 0.59, 0.52, 0.44 and 0.42 g/g,
respectively. The larvicidal LC50 values of fennel oil, Mg-LDH-F, and Ni-LDH-F were 843.88, 451.95,
550.12 ppm, respectively, whereas the corresponding values of green tea were 938.93, 530.46, and
769.94 ppm. The larval reduction percentage of fennel oil and Mg-LDH-F reached 90.1 and 96.2%,
24 h PT and their persistence reached five and seven days PT, respectively. The reduction percentage
of green tea oil and Mg-LDH-GT reached 88.00 and 92.01%, 24 h PT and their persistence reached five
and six days PT, respectively. Against adults, Mg-LDH-GT and Ni-LDH-GT were less effective than
green tea oil as their LC95 values were 5.45, 25.90, and 35.39%, respectively. The reduction in adult
density PT with fennel oil, Mg-LDH-F, green tea oil, and Mg-LDH-GT reached 83.1, 100, 77.0, and
99.0%, respectively, 24 h PT and were effective for three days. Mg-LDH-GT and Mg-LDH-F increased
the predation Cybister tripunctatus (71% and 69%), respectively; (4) Conclusions: For the first time,
Mg-LDH-GT and Mg-LDH-F was the best system loaded with relatively good desorption release to
its active ingredients and significantly affected Cx. pipiens larvae and adults in both laboratory and
field circumstances, and it could be included in mosquito control. |
