Chemical Composition, Larvicidal and Molluscicidal Activity of Essential Oils of Six Guava Cultivars Grown in Vietnam

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 (<i>E</i>)-β-caryophyllene and the other of limonene/(<i>E</i>)-β-caryophyllene. The essential oils PG03 and PG05 show promise as environmentally friendly pesticides when used to control <i>Aedes</i> mosquito larvae with values of 24 h LC_{50-<i>aegypti</i>} of 0.96 and 0.40 µg/mL while 24 h LC_{50-<i>albopictus</i>} of 0.50 and 0.42 µg/mL. These two essential oils showed selective toxicity against <i>Aedes</i> mosquito larvae and were safe against the non-target organism <i>Anisops bouvieri</i>. Other essential oils may be considered as molluscicides against <i>Physa acuta</i> (48 h LC₅₀ of 4.10 to 5.00 µg/mL) and <i>Indoplanorbis exustus</i> (48 h LC₅₀ of 3.85 to 7.71 µg/mL) and with less toxicity to <i>A. bouvieri</i>.