Three indigenous Thai medicinal plants for control of Aedes aegypti and Culex quinquefasciatus.

The potential larvicidal activity and insect growth regulator (IGR) properties of three selected indigenous medicinal Thai plants were tested against two species of mosquito with special reference to the late 3rd and early 4th instar larvae (L3 and L4, respectively). In case of larvicidal activity, Thevetia peruviana was the most potent, followed by Pueraria mirifica, and Butea superba was the least effective. In all cases, the late 3rd instar was more susceptible than the early 4th instar larvae, and the 48-hours exposure yielded more potent larvicidal activity than 24-hours exposure. However, at sublethal dosages, both P. mirifica and B. superba showed some dispersed effects interfering with ecdysis. A variety of toxic effects were observed and recorded in eight categories according to the stage of metamorphosis when death occurred. P. mirifica rendered the main deleterious effects in the pupa-adult period in both instar of Ae. aegypti and Cx. quinquefasciatus, whereas B. superba showed highest effect in black-pupa period of the late 3rd instar larval stage. The results were reversed for the early 4th instar larvae of both species of mosquito as the main effect appeared in the pupa-adult category. The overall results indicated that T. peruviana did not show any IGR properties; whereas, P. mirifica and B. superba seemed to exhibit the juvenile hormone type activity which resulted in abnormal death at various stages of development. B. superba was more promising than P. mirifica, and Ae. aegypti was about 2 times more susceptible than Cx. quinquefasciatus. In addition, L3 was always more susceptible than L4 with both mosquito species.

Mutagenicity of Pueraria mirifica Airy Shaw & Suvatabandhu and antimutagenicity of Thunbergia laurifolia Linn.

Thunbergia laurifolia Linn has been reputed to have antitoxic effects for all toxic substances. In this present study, we evaluated its effect against the mutagenicity induced by aqueous extracts from Pueraria mirifica Airy Shaw & Suvatabundhu in male rats. The formation of micronuclei in polychromatic erythrocytes was induced by oral administration of an aqueous extract of P. mirifica at the doses of 400, 600, and 800 mg/kg to the rats for 30 days. The results were that the extracts of P. mirifica at doses of 600 and 800 mg/kg acted as a mutagenic agent by inducing higher frequencies of micronuclei as compared to the controls. For the antimutagenic test, P. mirifica extract at a dose of 600 mg/kg (minimal effective dose) was mixed with fresh and dried extracts of T. laurifolia in proportions of 7:3 and 1:1, respectively. The results of 4-week-treatment indicated that aqueous extracts of T. laurifolia, prepared by both fresh and dry methods, could significantly inhibit the induction of micronuclei as induced by P. mirifica. It could be concluded from the results that, under certain circumstances, T. laurifolia exhibits a significant antimutagenic activity. The use of P. mirifica and T. laurifolia as fusion herbal medicines is suggested.