Eumporn Rattanachanpichai

Adulticidal activity against Stegomyia aegypti (Diptera: Culicidae) of three Piper spp.

Three Piper species, Piper longum, P. ribesoides and P. sarmentosum, were selected for investigation of adulticidal potential against Stegomyia aegypti, a main vector of dengue and dengue haemorrhagic fever. Successive extraction by maceration with 95% ethanol showed percentage yields of ethanolic extracts, which derived from P. longum, P. ribesoides and P. sarmentosum, of 8.89, 3.21 and 5.30% (w/w), respectively. All Piper extracts illustrated an impressive adulticidal activity when tested against female mosquitoes by topical application. The susceptibility of St. aegypti females to ethanol-extracted Piper was dose dependent and varied among the plant species. The highest adulticidal effect was established from P. sarmentosum, followed by P. ribesoides and P. longum, with LD50 values of 0.14, 0.15 and 0.26 microg/female, respectively. The potential of these Piper species, as possible mosquitocides, established convincing activity for further researches to develop natural substances for combat against adult mosquitoes.

Repellent properties of celery, Apium graveolens L., compared with commercial repellents, against mosquitoes under laboratory and field conditions

In our search for new bioactive products against mosquito vectors, we reported the slightly larvicidal and adulticidal potency, but remarkable repellency of Apium graveolens both in laboratory and field conditions. Repellency of the ethanolic preparation of hexane‐extracted A. graveolens was, therefore, investigated and compared with those of 15 commercial mosquito repellents including the most widely used, DEET. Hexane‐extracted A. graveolens showed a significant degree of repellency in a dose‐dependent manner with vanillin added. Ethanolic A. graveolens formulations (10–25% with and without vanillin) provided 2–5 h protection against female Aedes aegypti. Repellency that derived from the most effective repellent, 25% of hexane‐extracted A. graveolens with the addition of 5% vanillin, was comparable to the value obtained from 25% of DEET with 5% vanillin added. Moreover, commercial repellents, except formulations of DEET, showed lower repellency than that of A. graveolens extract. When applied on human skin under field conditions, the hexane‐extracted A. graveolens plus 5% vanillin showed a strong repellent action against a wide range of mosquito species belonging to various genera. It had a protective effect against Aedes gardnerii, Aedes lineatopennis, Anopheles barbirostris, Armigeres subalbatus, Culex tritaeniorhynchus, Culex gelidus, Culex vishnui group and Mansonia uniformis. The hexane‐extracted A. graveolens did not cause a burning sensation or dermal irritation when applied to human skin. No adverse effects were observed on the skin or other parts of the human volunteers’ body during 6 months of the study period or in the following 3 months, after which time observations ceased. Therefore, A. graveolens can be a potential candidate for use in the development of commercial repellents that may be an alternative to conventional synthetic chemicals, particularly in community vector control applications.

Mosquito repellency of the seeds of celery (Apium graveolens L.).

Abstract When the mosquito repellencies of four fractions of Apium graveolens seeds (one hexane, two dichloromethane and one methanolic) were investigated in the laboratory, all four were found to offer human volunteers some protection against female, adult Aedes aegypti. The hexane fraction, however, was found to exhibit the highest repellency in the laboratory, with median effective doses (ED50) and ED95 of 0.41 and 2.93 mg/cm2 skin, respectively. Only this fraction, which was also found to provide protection against mosquito bites for 3.5 h when applied, in the laboratory, at a concentration of 250 mg/ml, was then investigated for its repellency in the field and its stability. In storage, it was found to retain its repellency for at least 2 months, although significant reductions in its repellency were observed (in terms of shortened complete-protection times) after 3 months, whatever the temperature of storage (-20°C, 4°C, or room temperature). When applied to the skin of volunteers under field conditions, the hexane fraction showed strong repellent activity against a wide range of mosquito species belonging to various genera (Ae. gardnerii, Ae. lineatopennis, Armigeres subalbatus, Culex tritaeniorhynchus, Cx. vishnui group, Cx. quinquefasciatus and Mansonia uniformis). It appeared not to cause dermal irritation or any other adverse effect, either during 6 months of use or in the following 3 months of follow-up. Mosquito repellents based on extracts of Ap. graveolens seeds could be developed commercially, as an effective personal-protection measure against mosquito bites and the diseases caused by mosquito-borne pathogens.

Evaluation of the colchicine-like activity of Gloriosa superba-extracted fractions for mosquito (Diptera: Culicidae) cytogenetic study

Abstract Four fractions of Gloriosa superba L., i.e., hexane fraction, dichloromethane fraction 1, dichloromethane fraction 2, and methanol fraction, were investigated for colchicine-like activity using a mosquito cytogenetic assay. The results revealed that the latter three fractions yielded promisingly high colchicine-like activity, whereas the hexane fraction yielded very low activity compared with 1% colchicine in a 0.85% sodium chloride solution. The metaphase rates and average number of metaphase chromosomes per positive brain ganglion (range) of Aedes aegypti L. larvae after incubation with 0.25–2% solutions of dichloromethane fraction 1, dichloromethane fraction 2, 0.5–2% solutions of methanol fraction, and 1% colchicine solution were 90–100% and 7 (2–19) to 22 (7–47); 90–100% and 4 (1–11) to 30 (4–73); 95–100% and 11 (1–28) to 17 (2–62); and 100% and 6 (2–11), respectively. The temperature stability tests of the three promising fractions were performed by heating 0.5% working solution at 121°C for 15 min and preparing 0.5% working solution from stock frozen at −20°C for 10 mo. These fractions also yielded satisfactory outcomes of metaphase rates and an average number of metaphase chromosomes per positive brain ganglia compared with 1% colchicine solution.