ABSTRACT
Diseases transmitted by mosquitoes and snails cause a large burden of disease in less developed countries, especially those with low-income levels. An approach to control vectors and intermediate hosts based on readily available essential oils, which are friendly to the environment and human health, may be an effective solution for disease control. Guava is a fruit tree grown on a large scale in many countries in the tropics, an area heavily affected by tropical diseases transmitted by mosquitoes and snails. Previous studies have reported that the extracted essential oils of guava cultivars have high yields, possess different chemotypes, and exhibit toxicity to different insect species. Therefore, this study was carried out with the aim of studying the chemical composition and pesticide activities of six cultivars of guava grown on a large scale in Vietnam. The essential oils were extracted by hydrodistillation using a Clevenger-type apparatus for 6 h. The components of the essential oils were determined using gas-chromatography-mass-spectrometry (GC-MS) analysis. Test methods for pesticide activities were performed in accordance with WHO guidelines and modifications. Essential oil samples from Vietnam fell into two composition-based clusters, one of (E)-ß-caryophyllene and the other of limonene/(E)-ß-caryophyllene. The essential oils PG03 and PG05 show promise as environmentally friendly pesticides when used to control Aedes mosquito larvae with values of 24 h LC50-aegypti of 0.96 and 0.40 µg/mL while 24 h LC50-albopictus of 0.50 and 0.42 µg/mL. These two essential oils showed selective toxicity against Aedes mosquito larvae and were safe against the non-target organism Anisops bouvieri. Other essential oils may be considered as molluscicides against Physa acuta (48 h LC50 of 4.10 to 5.00 µg/mL) and Indoplanorbis exustus (48 h LC50 of 3.85 to 7.71 µg/mL) and with less toxicity to A. bouvieri.
ABSTRACT
A new fern species, Tectariadanangensis (Tectariaceae) from Vietnam, which had long been misreported as T.crenata, is described and illustrated. The new species resembles T.poilanei, a species long neglected in the fern flora of Indochina, in the frond shape and sori arrangement, but differs by its irregularly 2-rowed sori (versus regularly 2-rowed, distantly and evenly arranged) between lateral veins of pinnae, fronds being more or less dimorphic (versus monomorphic) and basal pinnae each with a base-joined (versus free) lobe. Phylogenetic analyses of five plastid regions (atpB, ndhF + ndhF-trnN, rbcL, rps16-matK + matK and trnL-F) suggested T.danangensis has a close affinity to T.harlandii. Tectariadanangensis appears to be an intermediate species between T.harlandii and T.poilanei.
ABSTRACT
Dichocarpum hagiangense from Ha Giang province, northern Vietnam is described and illustrated. Diagnostic features of the new species are a short rhizomatous stem, (2-)3-foliolate or simple leaves, and pink-purple flowers. The described species is distinct from closely allied D. trifoliolatum in having longer sepals, shape and obcordate apex of petal limbs, shorter flower stem, number and tooth shape of basal leaves; it differs from D. basilare and D. carinatum in having stem leaf, retuse apex and longer of central leaflet, number and (2-)3-foliated (or simple) of leaf. With the support of molecular data, the new species was clearly distinguished from other species in the Dichocarpum group by eight autapomorphic characters in nrITS sequence. A key to all species of Dichocarpum is provided. We suggest the IUCN conservation status of D. hagiangense to be "Critically Endangered". A newest checklist of the family Ranunculaceae in Vietnam is updated.