Chemical compositions and anti-mosquito activity of essential oils from Pericarpium Citri Reticulataes of different aging years

Mosquitoes are well-known vectors of malaria, dengue fever, chikungunya, yellow fever, Zika and many other diseases, and have become a great threat to public health. Nowadays, chemical insecticides are widely used for the control of mosquitoes. However, their widespread use has created some serious problems, such as insecticide resistance, environmental pollution, and toxicity to human beings. With the objectives to develop novel botanical and eco-friendly insecticides for mosquitoes, in this study we examined the chemical compositions of the essential oils (EOs) from different aging years of Pericarpium Citri Reticulatae (PCR, Guangchenpi in Chinese), and investigated their anti-mosquito activity in details. As a result, 39, 44, 48, and 40 main components were identified from the 1-, 5-, 10-, and 15-year PCR EOs, respectively. For each PCR EO, D-limonene (47.90–56.39%) and γ-terpinene (14.98–17.03%) were the major components. These PCR EOs showed potent larvicidal activity against Aedes albopictus (A. albopictus) larvae (LC₅₀ = 54.50–68.23 ppm ppm), and some of the major components were also very active, including D-limonene (LC₅₀ = 56.17 ppm), γ-terpinene (LC₅₀ = 64.28 ppm), β-myrcene (LC₅₀ = 54.51 ppm) and terpinolene (LC₅₀ = 57.69 ppm). These PCR EOs exhibited similar larvicidal activity, and their insecticidal activity may be attributed to the major constituents such as D-limonene, γ-terpinene and terpinolene. In addition, thymol was found more effective against A. albopictus adults (LC₅₀ = 96.82 ppm) than the other components, such as methyl 2-(methylamino) benzoate (LC₅₀ = 382.10 ppm) and α-terpineol (LC₅₀ = 507.54 ppm), and this compound could be one of the active components responsible for the adulticidal activity. Enzyme inhibition assays suggested that the activity of acetylcholinesterase, mixed function oxidase and esterase were significantly inhibited, which may result in the mortality of A. albopictus larvae. The present findings clearly demonstrated that naturally-occurring PCR EOs and the functional components display potent insecticidal activity against A. albopictus larvae and adults, and therefore, strongly suggest that PCR EOs and the main components are exploitable as botanical insecticides for the control of mosquitoes.