Chemical Composition, Antioxidant, and Mosquito Larvicidal Activity of Essential Oils from Hyptis capitata Jacq

Mortality and morbidity associated with vector-borne diseases, particularly those caused by mosquitoes, are increasing and new means of controlling them, including bio-larvicides, are needed. Malaria is a serious threat in many countries of Africa and Asia, and eco-friendly vector preventing measures are very much essential. Plant-derived larvicides are of great importance in this context. Hyptis capitata is an aromatic medicinal plant which is widely distributed in tropical countries. The aim of the present study is to examine the chemical composition, antioxidant and mosquito larvicidal effects of essential oils of this plant, extracted by hydro-distillation.

Chemical compositions of essential oils were analyzed using gas chromatography-mass spectrometry (GC-MS). Antioxidant activity was tested by the 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl (DPPH) assay and the mosquito larvicidal activity was checked against the fourth instar larvae of the malarial vector Anopheles stephensi. Fingerlings of Oreochromis mossambicus were used as a bio-model for toxicity studies.

A total of 48 constituents, inclusive of 44 (94.67%) from inflorescence and 19 (97.09%) from leaf oil were identified; δ-cadinene (14.68%) and linalool (6.99%) were the major constituents of the inflorescence oil, while leaf oil contained 1-octen-3-ol (34.08%), methyl linoleate (17.2%), and germacrene D (11.16%). Antioxidant analysis showed an effective concentration (EC₅₀) value of 22.76 μg/mL for leaf oil and 26.18 μg/mL for the inflorescence oil, corresponding to 17.57 μg/mL of ascorbic acid. Both oils showed a respectable larvicidal effect and the lethal concentrations (LC₅₀) are 39.08 μg/mL and 33.19 μg/mL for the inflorescence and leaf oil, respectively. Notably, both the inflorescence and leaf oils are not very toxic to fish with respect to the concentrations tested.

This study showed that the essential oils extracted from the leaves and inflorescences of H. capitata are effective antioxidants and can act as inexpensive mosquito larvicidal agents.