Enhanced Excito-Repellency of Binary Mixtures of Plant-Based Mosquito Repellents Against Culex quinquefasciatus Say (Diptera: Culicidae), a Night Biting Mosquito Species.

Efficacies of essential oils (EOs) of Vetiveria zizanioides (L.) Nash. (Poales: Poaceae) (VZ EO), Cananga odorata (Lam) Hook. F. & Thomson (Magnoliales: Annonaceae) (CO EO), and crude extract (CE) of Andrographis paniculata (Burm.F.) Wall ex. Nees (Lamiales: Acanthaceae) (AP CE), against laboratory (lab) and field strains of Culex quinquefasciatus Say were investigated. Irritant and repellent activities of individual and binary mixtures of plant extracts were compared with N,N-diethyl-m-toluamide (DEET) using an excito-repellency system. The irritant activity (direct tarsal contact), the mean percent escape response of VZ EO (91.67%, 83.33%), and CO EO (80%, 88.33%) were not significantly different compared with DEET (88.33%, 95%) against lab and field strains, respectively. Similarly, irritant responses in combinations (1:1 and 1:2, v:v) of either VZ EO or CO EO with AP CE were not significantly different from DEET against both strains (P > 0.001). The repellent activity (no tarsal contact), the mean percent escape response of VZ EO (68.33%), CO EO (61.67%), and VZ EO+AP CE (1:1, v:v) (81.67%) against lab strain and CO EO (85%) against field strain were not significantly different from that of DEET (P > 0.001). Interestingly, the greatest contact irritancy of VZ EO+AP CE (1:1, v:v) (96.67%) (P = 0.0026) and a stronger repellency response of CO EO (85%) (P = 0.0055) produced significantly different patterns of escape response compared with DEET against both lab and field strains, respectively. The EOs of VZ EO and CO EO or their mixture with AP CE showed potential as plant-based active ingredients for mosquito repellents. In addition, the major chemical constituents of VZ EO were ß-vetivone (6.4%), khusimol (2.96%), and α-vetivone (2.94%) by gas chromatograpy-mass spectrometry.

Comparative Excito-Repellency of Three Cambodian Plant-Derived Extracts Against Two Mosquito Vector Species, Aedes aegypti and Anopheles minimus.

A study of the behavioral responses of Aedes aegypti and Anopheles minimus to 3 Cambodian plant extracts at 3 different concentrations (1%, 2.5%, and 5%) was performed using an excito-repellency test system. These 3 plants were Strophanthus scandens, Capparis micracantha, and Dioscorea hispida, selected according to traditional healer's knowledge, bibliographic studies and market surveys. Results showed that S. scandens leaves' hexane extract was the only one to exert repellency against Ae. aegypti with 23.3% of escaped mosquitoes at a concentration of 5%. Capparis micracantha was responsible for an irritant activity against An. minimus with 20.2% of escaped mosquitoes at a concentration of 2.5% and 22.8% escaping at a concentration of 5%. Dioscorea hispida showed an irritant activity on both mosquito species with 23.2% of escaped Ae. aegypti at a concentration of 5% and about 20% of escaped An. minimus at 2.5% and 5%. This is the first report on the irritant and repellent activities of S. scandens , D. hispida , and C. micracantha against mosquito species.

Avoidance Behavior to Essential Oils by Anopheles minimus, a Malaria Vector in Thailand.

Essential oils extracted from 4 different plant species--citronella (Cymbopogon nardus), hairy basil (Ocimum americanum), sweet basil (Ocimum basilicum), and vetiver (Vetiveria zizanioides)-were investigated for their irritant and repellent activities against Anopheles minimus, using an excito-repellency test system. Pure essential oils were used in absolute ethanol at the concentrations of 0.5%, 1%, 2.5%, and 5% (v/v) compared with deet. At the lowest concentration of 0.5%, hairy basil displayed the best irritant and repellent effects against An. minimus. Citronella and vetiver at 1-5% showed strong irritant effects with>80% escape, while repellent effects of both oils were observed at 1% and 2.5% citronella (73-89% escape) and at 5% vetiver (83.9% escape). Sweet basil had only moderate irritant action at 5% concentration (69.6% escape) and slightly repellent on test mosquitoes (<50% escape). The results found that hairy basil, citronella, and vetiver are promising potential mosquito repellent products for protection against An. minimus.