Biochemical Effects of Petroselinum crispum (Umbellifereae) Essential Oil on the Pyrethroid Resistant Strains of Aedes aegypti (Diptera: Culicidae).

In ongoing screening research for edible plants, Petroselinum crispum essential oil was considered as a potential bioinsecticide with proven antimosquito activity against both the pyrethroid susceptible and resistant strains of Aedes aegypti. Due to the comparative mosquitocidal efficacy on these mosquitoes, this plant essential oil is promoted as an attractive candidate for further study in monitoring resistance of mosquito vectors. Therefore, the aim of this study was to evaluate the impact of P. crispum essential oil on the biochemical characteristics of the target mosquito larvae of Ae. aegypti, by determining quantitative changes of key enzymes responsible for xenobiotic detoxification, including glutathione-S-transferases (GSTs), α- and ß-esterases (α-/ß-ESTs), acetylcholinesterase (AChE), acid and alkaline phosphatases (ACP and ALP) and mixed-function oxidases (MFO). Three populations of Ae. aegypti, comprising the pyrethroid susceptible Muang Chiang Mai-susceptible (MCM-S) strain and the pyrethroid resistant Pang Mai Dang-resistant (PMD-R) and Upakut-resistant (UPK-R) strains, were used as test organisms. Biochemical study of Ae. aegypti larvae prior to treatment with P. crispum essential oil revealed that apart from AChE, the baseline activity of most defensive enzymes, such as GSTs, α-/ß-ESTs, ACP, ALP and MFO, in resistant UPK-R or PMD-R, was higher than that determined in susceptible MCM-S. However, after 24-h exposure to P. crispum essential oil, the pyrethroid susceptible and resistant Ae. aegypti showed similarity in biochemical features, with alterations of enzyme activity in the treated larvae, as compared to the controls. An increase in the activity levels of GSTs, α-/ß-ESTs, ACP and ALP was recorded in all strains of P. crispum oil-treated Ae. aegypti larvae, whereas MFO and AChE activity in these mosquitoes was decreased. The recognizable larvicidal capability on pyrethroid resistant Ae. aegypti, and the inhibitory effect on AChE and MFO, emphasized the potential of P. crispum essential oil as an attractive alternative application for management of mosquito resistance in current and future control programs.

Synergy in the adulticidal efficacy of essential oils for the improvement of permethrin toxicity against Aedes aegypti L. (Diptera: Culicidae).

BACKGROUND: In a previous screening program for mosquitocides from local edible plants in Thailand, essential oils (EOs) of Cyperus rotundus, Alpinia galanga and Cinnamomum verum, were found to possess promising adulticidal activity against Aedes aegypti. With the aim of reducing usage of conventional insecticides and improving the management of resistant mosquito populations, this study was designed to determine the potential synergism in the adulticidal efficacy of EOs on permethrin toxicity against Ae. aegypti, both pyrethroid-resistant and -susceptible strains. METHODS: EOs extracted from rhizomes of C. rotundus and A. galanga as well as C. verum barks were evaluated for chemical compositions and adulticidal activity against Muang Chiang Mai-susceptible (MCM-S) and Pang Mai Dang-resistant (PMD-R) strains of Ae. aegypti. Adulticidal bioassays of EO-permethrin mixtures for synergistic activity were also performed on these Ae. aegypti strains. RESULTS: Chemical characterization by the GC-MS analytical technique demonstrated that 48 compounds were identified from the EOs of C. rotundus, A. galanga and C. verum, representing 80.22%, 86.75% and 97.24%, respectively, of all compositions. Cyperene (14.04%), ß-bisabolene (18.27%) and cinnamaldehyde (64.66%) were the main constituents of C. rotundus, A. galanga and C. verum oils, respectively. In adulticidal bioassays, EOs of C. rotundus, A. galanga and C. verum were effective in killing Ae. aegypti, both MCM-S and PMD-R strains, with LD50 values of 10.05 and 9.57 µg/mg female, 7.97 and 7.94 µg/mg female, and 3.30 and 3.22 µg/mg female, respectively. The adulticidal efficacy against MCM-S and PMD-R Ae. aegypti of these EOs was close to that of piperonyl butoxide (PBO, LD50 values = 6.30 and 4.79 µg/mg female, respectively) but less pronounced than that of permethrin (LD50 values = 0.44 and 3.70 ng/mg female, respectively). Nevertheless, combination-based bioassays discovered the accomplished synergism of EOs together with permethrin. Significant synergistic effects with permethrin against both the strains of Ae. aegypti were recorded in the EOs of C. rotundus and A. galanga. Addition of C. rotundus and A. galanga oils decreased the LD50 values of permethrin against MCM-S dramatically from 0.44 to 0.07 and 0.11 ng/mg female, respectively, with synergism ratio (SR) values of 6.28 and 4.00, respectively. Furthermore, EOs of C. rotundus and A. galanga also reduced the LD50 values of permethrin against PMD-R drastically from 3.70 to 0.42 and 0.003 ng/mg female, respectively, with SR values of 8.81 and 1233.33, respectively. CONCLUSIONS: The synergy of enhanced adulticidal toxicity recorded from EO-permethrin combinations against both strains of Ae. aegypti presents a promising role of EOs as a synergist for improving mosquitocidal efficacy, particularly in situations where conventional compounds are ineffective or inappropriate.

Assessment of Angelica sinensis (Oliv.) Diels as a repellent for personal protection against mosquitoes under laboratory and field conditions in northern Thailand.

BACKGROUND: Angelica sinensis (Oliv.) hexane extract (AHE) has been reported as a proven and impressive repellent against laboratory-reared female Aedes aegypti mosquitoes. With the aim of promoting products of plant origin as a viable alternative to conventional synthetic substances, this study was designed to transform AHE-based repellents for exploitable commercial production by enhancing their efficacy and assessing their physical and biological stability as well as repellency against mosquitoes under laboratory and field conditions. METHODS: The chemical profile of AHE was analyzed by qualitative gas chromatography-mass spectrometry (GC-MS) technique. AHE was supplemented with vanillin, as a fixative, and then investigated for repellency and comparison to the standard synthetic repellent, DEET, under both laboratory and field conditions. Determination of physical and biological stability as a repellent was carried out after keeping AHE samples under varying temperatures and for different storage times. RESULTS: GC-MS analysis revealed that AHE contained at least 21 phytochemical compounds, constituting 95.74 % of the total content, with the major constituent of 3-N-butylphthalide (66.67 %). Ethanolic formulations of AHE and DEET showed improvement of repellency in a dose-dependent manner when vanillin was added in laboratory assessment. While 5-25 % AHE alone provided median complete-protection times of 2.0-6.5 h against Ae. aegypti, these times were increased to 4.0-8.5 h with a combination of AHE and 5 % vanillin (AHEv). Protection times against Ae. aegypti were extended from 2.25 to 7.25 h to 4.25-8.25 h when 5-25 % DEET was combined with 5 % vanillin (DEETv). In determining stability, all stored AHE samples exhibited similar characteristics such as liquid phases with aromatic odor comparable to those of fresh preparations. Furthermore, repellent activity of stored AHE samples lasted for at least six months, with varied efficacy (4.5-10.0 h) against Ae. aegypti. Field trials revealed strong repellency from both 25 % AHEv and 25 % DEETv, with complete protection (100 %) against a wide range of local mosquito populations. A total of 5,718 adult female mosquitoes, with the most predominant being Culex quinquefasciatus (41.47 %), Armigeres subalbatus (41.13 %), and Culex vishnui (10.53 %), was collected during field applications. No local skin reaction or other allergic responses was observed during both laboratory and field study periods. CONCLUSIONS: Angelica sinensis proved to have not only impressive repellency against both laboratory Ae. aegypti and a wide range of natural mosquito populations, but also relative stability in physical and biological performance.

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

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 Ligusticum sinense 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.