Comparative toxicity of cinnamon oil, cinnamaldehyde and their nano-emulsions against Culex pipiens (L.) larvae with biochemical and docking studies

The larvicidal activity of cinnamon oil and its main component, cinnamaldehyde, was compared with their nano-emulsions (NEs) against Culex pipiens mosquito larvae. Oil-in-water (O/W) NEs preparation was based on the coarse emulsion followed by high-energy ultra-sonication. The droplet size, polydispersity index (PDI), viscosity, zeta potential, and pH of NEs were investigated. The droplet sizes of the NEs were 95.67 nm for cinnamon oil and 174.59 nm for cinnamaldehyde. The NEs recorded high negative zeta potentials (-30.0 and -21.20 for cinnamon oil and cinnamaldehyde, respectively). The larvicidal activity results showed that the cinnamaldehyde (LC50 = 94.46 and 72.91 mg/l for T and NE, respectively) had higher activities than cinnamon oil (LC50 = 154.08 and 123.13 mg/l for T and NE, respectively) after 24 h of exposure against C. pipiens larvae. These results proved that NE formulation enhanced the activity of tested compounds against larvae. The in vitro effect on the acetylcholinesterase (AChE), adenosine triphosphatase (ATPase), and gamma-aminobutyric acid transaminase (GABA-T) were demonstrated, and the data proved that the NEs formulations were higher than their pure compounds. Non-formulated cinnamon oil and cinnamaldehyde caused 17.26% and 30.83% of AChE, respectively, while their NEs caused 46.40% and 60.59% inhibition. Furthermore, the molecular docking studies indicated that the affinity binding of cinnamaldehyde on AChE and GABA-T was higher than ATPase. This work describes bio-products with potential use against C. pipiens larvae as eco-friendly products

Preparation of Ecofriendly Formulations Containing Biologically Active Monoterpenes with Their Fumigant and Residual Toxicities against Adults of Culex pipiens

Different mixtures of monoterpenes (ketone, alcohol, and alkene) were loaded on paper discs and wax and their knockdown activities were evaluated against Culex pipiens adults. Some individual monoterpenes were also evaluated by residual toxicity technique. Citronella oil as a reference was also loaded separately or in combination with monoterpenes on paper discs and wax. The ketone monoterpenes mixture (camphor, menthone, carvone, and fenchone) on paper discs was the most active (KT50 = 17.20 min) followed by ketone monoterpenes with citronella oil (KT50 = 20.79 min) and citronella oil alone (KT50 = 28.72 min). Wax formulations proved that the ketone and alcohol (geraniol, thymol, and menthol) monoterpenes gave the most activity as knockdown (KT50 = 31.79 and 43.39 min, resp.). Alcohol monoterpenes formulation recorded KT50 = 43.39 min. Residual activity of tested individual monoterpenes reported that the menthol was more toxic than camphor and camphene. Generally, this study suggests that the monoterpenes have the properties, which make them used as eco-friendly compounds in the control programs of Cx. pipiens adult. The use of paper discs is more applicable than wax in the adulticidal formulations

The Antibacterial Activity of Chitosan Products Blended with Monoterpenes and Their Biofilms against Plant Pathogenic Bacteria

This study focuses on the biological activities of eleven chitosan products with a viscosity-average molecular weight ranging from 22 to 846 kDa in combination with the most active monoterpenes (geraniol and thymol), out of 10 tested, against four plant pathogenic bacteria, Agrobacterium tumefaciens, Erwinia carotovora, Corynebacterium fascians, and Pseudomonas solanacearum. The antibacterial activity was evaluated in vitro by the agar dilution technique as a minimum inhibitory concentration (MIC) that was found to be dependent on the type of the microorganism tested. The most active product of chitosan was used for biofilm production enriched with geraniol and thymol (0.1 and 0.5%) and the films were also evaluated against the tested bacteria. The biological bioactivities summarized here may provide novel insights into the functions of chitosan and some monoterpenes and potentially allow their use for food protection from microbial attack

Chemical composition of the essential oils isolated from peel of three citrus species and their mosquitocidal activity against <i>Culex pipiens</i>

<p>Three essential oils (EOs) were isolated from the peel of citrus fruits <i>Citrus reticulata</i> L.<i>, Citrus reticulata chinase</i> Blanco and <i>Citrus sinensis</i> (L.) Osbeck (Family: Rutaceae) and evaluated against <i>Culex pipiens</i> L.1758 (Family: Culicidae)<i>.</i> Chemical composition indicated that the EOs were rich in essential phytochemicals including hydrocarbons, monoterpenes and sesquiterpenes. These constituents revealed some variability among the oils displaying interesting chemotypes limonene (35–51%), 1<i>R</i>-α-pinene (1.04–2.5%), γ-terpinene (0.46–5.65%) and sabinene (0.51–5.42%). The toxicity proved that <i>C. sinensis</i> oil had more effect than <i>C. reticulata chinase</i> and <i>C. reticulata</i> oils against larvae (LC₅₀ = 15.35, 16.11 and 32.84 mg/L, respectively). However, <i>C. reticulate</i> was the most active as fumigant against adults (LC₅₀ 2.74 μL/L air). The <i>in vivo</i> effect on acetylcholine esterase (AChE), carboxyl esterase (CbE), acid phosphatase (ACP), alkaline phosphatase (ALP), adenosine triphosphatase (ATPase) and glutathione-S-transferase (GST) were also demonstrated. To the best of our knowledge, this is the first report about the chemical composition and mosquitocidal activity of <i>C. reticulata chinase</i> essential oils. Conclusively, the tested essential oils could be used as eco-friendly alternatives in mosquitoes control programme.</p