Leptospermum scoparium essential oil is a promising source of mosquito larvicide and its toxicity is enhanced by a biobased emulsifier

Abstract

Synthetic pesticides are the cornerstone of vector-borne disease control, but alternatives are urgently needed to tackle the growing problem of insecticide resistance and concerns over environmental safety. Leptospermum scoparium J.R. Forst and G. Forst (manuka) essential oil and its four fractions were analyzed for chemical composition and toxicity against Aedes aegypti larvae. The use of bio-based amylose-N-1-hexadecylammonium chloride inclusion complexes (Hex-Am) as an emulsifier for L. scoparium essential oil was also investigated. Fraction 1 was inactive, fractions 2 (LC 50 = 12.24 ppm) and 3 (LC 50 = 20.58 ppm) were more toxic than the whole essential oil (LC 50 = 47.97 ppm), and fraction 4 (LC 50 = 35.87 ppm) had similar toxicity as the whole essential oil. Twenty-one chemical constituents were detected in L. scoparium essential oil compared to 16, 5, 19 and 25 chemical constituents in fractions, 1, 2, 3 and 4 respectively. The two most dominant chemical constituents were calamenene (17.78%) and leptospermone (11.86%) for L. scoparium essential oil, calamenene (37.73%) and ledene (10.37%) for fraction 1, leptospermone (56.6%) and isoleptospermone (19.73) for fraction 2, cubenol (24.30%) and caryophyllene oxide (12.38%) for fraction 3, and γ-gurjunene (21.62%) and isoleptospermone (7.88%) for fraction 4. Alpha-pinene, ledene, and aromandendrene were 2-7 times less toxic than the whole essential suggesting that the toxicity of L. scoparium essential oil was either due to other chemical constituents that were not tested or due synergist interactions among chemical constituents. Leptospermum scoparium essential oil-Hex-Am emulsion (LC 50 = 29.62) was more toxic than the whole essential oil. These findings suggest that L. scoparium essential oil is a promising source of mosquito larvicide and that Hex-Am is an excellent emulsifier for L. scoparium essential oil for use as a larvicide.

Mānuka Oil—A Review of Antimicrobial and Other Medicinal Properties

“…Antibacterial effect against S. aureus and MRSA was shown. [12,21] Major constituent of mānuka oil; contributes to insecticidal, antiseptic, bactericidal, analgesic and anti-inflammatory properties.…”

Morphoanatomical study, seasonal variation, and larvicidal activity of volatile oils from the leaves of Campomanesia pubescens (DC.) O. Berg (Myrtaceae)

“…J.W. Moore (LC50 27μg/mL) (Leyva, et al, 2009), Psidium guajava L. (LC50 24.7μg/mL) (Lima, et al, 2011b), Leptospermum scoparium J.R. Forst and G. Forst (LC50 47.97ppm) (Muturi, et al, 2020), Callistemon citrinus (Curtis) Skeels LC50 17.3 µg/mL (An, et al, 2020), and Melaleuca leucadendra (L.) L (LC50 1.4µg/mL) (An, et al, 2020). Volatile oils are an interesting source of new insecticidal molecules, mainly because they are biodegradable and have low toxicity (Isman, 2020;Viana, et al, 2018).…”

Biosynthesis of Lemongrass Essential Oil and the Underlying Mechanism for Its Insecticidal Activity

“…Along with cytotoxicity, EOs are attributed to cause neurological damages and organ-failure in target organisms (Afify et al, 2019). Other sublethal effects can include irritation, repellence and complications in reproduction and proliferation (Muturi et al, 2020). Essential oils can induce detrimental responses in storedproduct insects by entering into their digestive system (Devi et al, 2019).…”

“…These bioactive compounds, however, carry substantial insecticidal and repellent activities against various insects, including common housefly and malarial vector mosquitoes (Mokhtari et al, 2020). However, percentage abundance of these constituents can vary depending on the geography, temperature, plant developmental stage, method used for essential oil extraction as well as the solvent used for the extraction (Muturi et al, 2020). Given such dynamic composition, different responses or varying severity of such responses against the same insect can be exhibited by the essential oils (Al-Sarar et al, 2020).…”