Remarkable repellency of Ligusticum sinense (Umbelliferae), a herbal alternative against laboratory populations of Anopheles minimus and Aedes aegypti (Diptera: Culicidae)

Abstract

BackgroundFor personal protection against mosquito bites, user-friendly natural repellents, particularly from plant origin, are considered as a potential alternative to applications currently based on synthetics such as DEET, the standard chemical repellent. This study was carried out in Thailand to evaluate the repellency of Ligusticumsinense hexane extract (LHE) against laboratory Anopheles minimus and Aedes aegypti, the primary vectors of malaria and dengue fever, respectively.MethodsRepellent testing of 25% LHE against the two target mosquitoes; An. minimus and Ae. aegypti, was performed and compared to the standard repellent, DEET, with the assistance of six human volunteers of either sex under laboratory conditions. The physical and biological stability of LHE also was determined after keeping it in conditions that varied in temperature and storage time. Finally, LHE was analysed chemically using the qualitative GC/MS technique in order to demonstrate a profile of chemical constituents.ResultsEthanol preparations of LHE, with and without 5% vanillin, demonstrated a remarkably effective performance when compared to DEET in repelling both An. minimus and Ae. aegypti. While 25% LHE alone provided median complete-protection times against An. minimus and Ae. aegypti of 11.5 (9.0–14.0) hours and 6.5 (5.5–9.5) hours, respectively, the addition of 5% vanillin increased those times to 12.5 (9.0–16.0) hours and 11.0 (7.0–13.5) hours, respectively. Correspondingly, vanillin added to 25% DEET also extended the protection times from 11.5 (10.5–15.0) hours to 14.25 (11.0–18.0) hours and 8.0 (5.0–9.5) hours to 8.75 (7.5–11.0) hours against An. minimus and Ae. aegypti, respectively. No local skin reaction such as rash, swelling or irritation was observed during the study period. Although LHE samples kept at ambient temperature (21–35°C), and 45°C for 1, 2 and 3 months, demonstrated similar physical characteristics, such as similar viscosity and a pleasant odour, to those that were fresh and stored at 4°C, their colour changed from light- to dark-brown. Interestingly, repellency against Ae. aegypti of stored LHE was presented for a period of at least 3 months, with insignificantly varied efficacy. Chemical analysis revealed that the main components of LHE were 3-N-butylphthalide (31.46%), 2, 5-dimethylpyridine (21.94%) and linoleic acid (16.41%), constituting 69.81% of all the extract composition.ConclusionsLHE with proven repellent efficacy, no side effects on the skin, and a rather stable state when kept in varied conditions is considered to be a potential candidate for developing a new natural alternative to DEET, or an additional weapon for integrated vector control when used together with other chemicals/measures.

Bioactivities of 3-Butylidenephthalide and <i>n</i>-Butylbenzene from the Essential Oil of<i>Ligusticum jeholense</i> against Stored-product Insects

“…L. chuanxiong rhizome serves as traditional Chinese medicinal herb and its essential oil demonstrated contact toxicity against maize weevils, Sitophilus zeamais LD 50 13.09 μg/adult 22 . The hexane extract of L. sinense rhizomes possessed remarkable repellency in the control of Anopheles minimus and Aedes aegypti which were the primary vectors of malaria and dengue fever Diptera: Culicidae 23 .…”

Sustainable manufacture of insect repellents derived from Nepeta cataria

“…DEET, applied to the forearm, repelled Aedes aegypti , Anopheles quadrimaculatus , and Anopheles albimanus for 426 min, 96 min, and 87 min, respectively 29 . A 25% volume fraction of DEET in ethanol repelled Aedes aegypti for 8 h 30 . Whereas, Bernier found that a dose of 0.5 mg cm −2 of DEET applied to a muslin cloth patch was active for 24 h. Catnip’s oil is a better spatial repellent than DEET and demonstrated effective topical repellency properties 31 .…”

Who’s afraid of DEET? Fearmongering in papers on botanical repellents

“…Asadollahi et al state, "it has been identified that chemical repellents are not safe for public health " [1]. Besides the fact that every repellent, botanical or synthetic, is a chemical repellent, the sole source cited for this claim is a paper by Sanghong et al [2] promoting the herb Ligusticum sinense as "a herbal alternative" [sic] against mosquitoes. That paper not only does not test the safety of "chemical repellents" at all, but also actually states that DEET is "considered safe, " and that the rare, toxic effects attributed to it "have been described mainly after misapplication. "…”

“…Even if Asadollahi et al were confused about the nature of the repellent-insecticide resistance correlation, there is no basis for them to falsely claim that synthetic repellents differ from natural repellents in this regard. Their sources for the claim are again the paper by Sanghong et al [2], which does not state anything relating to the matter, and Govindaarajan et al [6], an article claiming Zingiber nimmonii is "an eco-friendly tool" against mosquitoes, and which, while also making debunked or incorrect claims about DEET, clearly states that the issues of ecological disruption are due to insecticides, not repellents.…”