Malar J. 2015; 14: 307.
Published online 2015 Aug 7. doi: 10.1186/s12936-015-0816-y
PMCID: PMC4527275
Remarkable repellency of Ligusticum sinense (Umbelliferae), a herbal alternative against laboratory populations of Anopheles minimus and Aedes aegypti (Diptera: Culicidae)
Abstract
Background
For
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.
Methods
Repellent 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.
Results
Ethanol
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.
Conclusions
LHE
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.
Keywords: Ligusticumsinense, Repellents, Mosquitoes, Anopheles minimus, Aedes aegypti
