Insecticidal Activity of Plectranthus amboinicus Essential Oil against the Stable Fly Stomoxys calcitrans (Diptera: Muscidae) and the Horse Fly Tabanus megalops (Diptera: Tabanidae)

Abstract

The stable fly, Stomoxys calcitrans (Diptera: Muscidae), and the horse fly, Tabanus megalops (Diptera: Tabanidae), are important ectoparasites of livestock in Thailand. These species affect animal health and cause economic losses. This study investigated the insecticidal activity of Plectranthus amboinicus essential oil against S. calcitrans and T. megalops through contact and fumigant toxicity tests and evaluated the effects of the essential oil on these flies through histopathological and scanning electron microscopic (SEM) studies. The results of the contact toxicity test indicated that the median lethal dose against S. calcitrans and T. megalops was 12.05 and 131.41 µg/fly, and the 90% lethal dose was 45.53 and 200.62 µg/fly, respectively. The results of the fumigant toxicity test showed that the median lethal concentration against S. calcitrans and T. megalops was 1.34 and 7.12 mg/L air, and the 90% lethal concentration was 4.39 and 30.37 mg/L air, respectively. Histopathology revealed neuronal degeneration in the brain of S. calcitrans and interstitial neuronal edema of the brain and ovarian necrosis in T. megalops. No external morphological changes were observed via SEM. Given its insecticidal properties against S. calcitrans and T. megalops, P. amboinicus essential oil could be developed into a natural insecticide to control these fly species.

Effects of Coleus amboinicus L. Essential Oil and Ethanolic Extracts on Planktonic Cells and Biofilm Formation of Microsporum canis Isolated from Feline Dermatophytosis

“…It also inhibits the biofilm formation of other pathogenic microorganisms, such as Streptococcus mutans, Streptococcus pyogenes, and S. aureus [ 50 , 51 , 52 ]. C. amboinicus is rich in monoterpenes, including carvacrol, thymol, eugenol, chavicol, and ethyl salicylate [ 37 , 49 , 53 ]. The 18 compounds identified in CEO in this study represent 99.84% of the total essential oil and include carvacrol (56.65%), p-cymene (10.89%), and γ-terpinene (9.33%); these three compounds alone comprise 76.87 % of the total essential oil.…”

“…This result differs from that reported by da Costa et al, who found thymol to be the major constituent (64.3%), followed by p-cymene (10.3%), γ-terpinene (9.9%), and β-caryophyllene (2.8%) [ 54 ]. Previous studies have reported that the phytochemical composition of CEO is significantly influenced by the cultivation location, processes, and methods of essential oil extraction [ 25 , 37 ]; for example, steam distillation produced higher levels of carvacrol in C. amboinicus essential oil than those produced via the hydrodistillation method [ 37 ]. CEO at MIC had excellent effects against all clinical isolates.…”

“…The physical properties of the CEO, including color, density, refractive index, and specific gravity, were evaluated and recorded. The yield of CEO was determined based on the weight of the fresh plant material before processing and was expressed in % ( v / w ) [ 37 ].…”

“…The stem, leaf, and root extracts of C. amboinicus contain high concentrations of polyphenolics such as caffeic acid, rosmarinic acid, apigenin, chrysoeriol, 5- O -methyl-luteolin, and 5,8-dihydroxy-7,2′,3′,5′-tetramethoxyflavone, which is a novel flavonoid [ 26 , 27 , 28 ]. Several studies have reported the wide range of pharmacological properties of C. amboinicus extracts and essential oil, including antioxidant activity [ 25 ], antidandruff action [ 29 ], antiproliferative effects on cancer cells [ 30 ], analgesic and anti-inflammatory activities [ 31 ], antirheumatoid arthritis [ 32 ], anti-inflammatory effect following bone injury [ 33 ], antibacterial activity against methicillin-resistant Staphylococcus aureus [ 34 ], mosquitocidal and water sedimentation properties [ 35 ], and insect repellent [ 36 ] and insecticidal effects [ 37 ].…”

Untitled

“…They consist of various secondary metabolites such as tannins, phenolic compounds, alkaloids, and flavonoids, which assist in enhancing growth and immunity responses 20 . P. amboinicus and O. sanctum comprise some main phytochemical constituents such as α-Cubebene, α-Copaene, alpha-Humulene, Beta-caryophyllene, Carvacrol, Eugenol, Para-cymene, Limonene, Apigenin, Rosmarinic acid, Ursolic acid, Oleanolic acid, Luteolin, Beta-sitosterol, etc., 17,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] . As per the literature study, these are typically the components of major interest with bioactive properties that are well established.…”