Insecticidal Activities of the Leaf Oils of Eight Cinnamomum. species Against Aedes aegypti. and Aedes albopictus.

Abstract

The leaf oils of eight Cinnamomum. species (C. rhyncophyllum. Miq., C. microphyllum. Ridl., C. pubescens. Kochummen, C. mollissimum. Hook. f., C. impressicostatum. Kosterm, C. scortechinii. Gamb., C. sintoc. Bl., and C. cordatum. Kosterm) were investigated for their larvicidal and adulticidal activities against Aedes aegypti. (Aedes aegypti Lynn) and Aedes albopictus. (Aedes albopictus Skuse). Acute mortalities of the fourth instar larvae and the adult mosquitoes were determined according to the standard WHO methods. Among the essential oils studied, the leaf oils of C. rhyncophyllum., C. microphyllum., C. pubescens., C. mollissimum., and C. impressicostatum. showed significant effects against the larvae of Ae. aegypti. and Ae. albopictus. with concentrations that caused 50% mortality (LC₅₀) values of less than 12.8 and 11.8 µg ml^?1, respectively. The essential oils that showed strong larvicidal effects also demonstrated relatively strong adulticidal effects on the mosquitoes after 3 h exposure with LC₅₀ values ranging from 133.0 to 243.0 µg ml^?1 against Ae. aegypti. and from 118.0 to 194.0 µg ml^?1 against Ae. albopictus.. The efficacy of the oils toward the larvae and adult mosquitoes of both species was nonselective as the LC₅₀ values showed little variation. The chemical composition of the oils was investigated by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). This study suggested that the essential oils containing high levels of benzyl benzoate and benzyl salicylate exhibited strong insecticidal activities against the larvae and adult mosquitoes.     

A study of the larvicidal activity of two Croton species from northeastern Brazil against Aedes aegypti

The essential oils of Croton heliotropiifolius Kunth (Euphorbiaceae) and Croton pulegiodorus Baill. were selected for larvicidal evaluation against Aedes aegypti L. (Diptera: Culicidae) and studied qualitatively and quantitatively by GC and GC-MS. Sixty-one compounds representing 92.03% (C. heliotropiifolius) and 85.68% (C. pulegiodorus) of the essential oils, respectively, have been identified. The major components of C. heliotropiifolius essential oil were identified as β-caryophyllene (35.82%), bicyclogermacrene (19.98%), and germacrene-D (11.85%). The major components in C. pulegiodorus essential oil were identified as β-caryophyllene (20.96%), bicyclogermacrene (16.89%), germacrene-D (10.55%), τ-cadinol (4.56%), and β-copaen-4-α-ol (4.35%). The essential oil of C. pulegiodorus (LC₅₀ 159 ppm) was more effective against Ae. aegypti than that of C. heliotropiifolius (LC₅₀ 544 ppm). In order to verify whether the major compound of both essential oils is the active principle responsible for the larvicidal activity, β-caryophyllene was purchased and its larvicidal potential was further evaluated. However, β-caryophyllene (LC₅₀ 1038 ppm) showed weak larvicidal potency. Results of larvicidal evaluation suggest the existence of a synergistic effect of minor components in the essential oils.     

Chemical composition of the essential oil and n-hexane extract of Stachys tmolea subsp. Tmolea Boiss., an endemic species of Turkey,and their mosquitocidal activity against dengue vector Aesdes aegypti

Stachys tmolea subsp. tmolea Boiss. is endemic to Turkey and is a species of the genus Stachys L. which is one of the largest genera of the family Lamiaceae with about 300 species. The aims of this study were to examine the chemical composition of the essential oil and n-hexane extract of S. tmolea subsp. tmolea as natural sources of insecticidal activity against the dengue vector, Aedes aegypti. Analysis of the essential oil by GC-FID and gas chromatography-mass spectrometry (GC-MS) systems identified hexahydrofarnesyl acetone (15%), viridiflorol (10%), hexadecanoic acid (7%) and 9-geranyl-p-cymene (6%) as major components. The volatile components of the n-hexane extract were extracted using headspace solid-phase microextraction (HS-SPME) and were analyzed using GC-MS. The principal constituents were 3,4-dimethyl decane (16%), 3-methyl-3-pentanol (15%), 2-methyl-2-pentanol (12%), 1,4-bis (1,1-dimethylethyl) benzene (12%), heptanal (10%), acetic acid (6%) and decane (4%). Bioassay of the n-hexane extract, at 5 µg/mosquito, produced 90% mortality against adult Ae. aegypti while the S. tmolea essential oil demonstrated 13% mortality. No larvicidal activity was observed both in essential oil and n-hexane extract. Further studies are needed to assess the adulticidal activity of the responsible compounds in the crude extract.