Mosquitocidal activities of Chenopodium botrys whole plant n-hexane extract against Culex quinquefasciatus

This research aimed to investigate various mosquitocidal activities of Chenopodium botrys whole- plant n-hexane extract against Culex quinquefasciatus. The extract showed remarkable larvicidal, pupicidal, adulticidal, oviposition deterrent and adult emergence inhibitory activities against Cx. quinquefasciatus. During the larvicidal and pupicidal activities, the 24-hour lethal concentration (LC50) of extract against 2nd instar larvae, 4th instar larvae and pupae were 324.6, 495.6 and 950.8 ppm, respectively. During the CDC (Centers for Disease Control and Prevention) bottle bioassay for adulticidal activity, the median knockdown times (KDT50) at 1.25% concentration was 123.4 minutes. During the filter paper impregnation bioassay for adulticidal activity, the KDT50 value at 0.138 mg/cm2 concentration was 48.6 minutes. The extract was fractionated into 14 fractions through silica gel column chromatography which were then combined into six fractions on the basis of similar retention factor (Rf) value. These fractions were screened for adulticidal activity by applying CDC bottle bioassay. The fraction obtained through 60:40 to 50:50% n-hexanes-chloroform mobile phase with 0.5 Rf value showed 100% adulticidal activity at 0.2% concentration. During oviposition deterrent activity, the highest concentration (1000 ppm) showed 71.3 ± 4.4% effective repellence and 0.6 ± 0.1 oviposition activity index. During adult emergence inhibition activity, the median emergence inhibition (EI50) value was 312.3 ppm. From the outcome of the present investigation, it is concluded that the n-hexane extract of C. botrys whole- plant possesses strong larvicidal, pupicidal, adulticidal, oviposition deterrent and adult emergence inhibitory activities against Cx. quinquefasciatus.

Adulticidal Activity of Metarhizium anisopliae s.l. (Hypocreales: Clavicipitaceae) Native Strains From Argentina Against Aedes aegypti (Diptera: Culicidae)

The adulticidal activity of six fungal strains of Metarhizium anisopliae (Metschn.) Sorokin s.l. (Hypocreales: Clavicipitaceae) against Aedes aegypti (L.) (Diptera: Culicidae) was assessed. These strains (CEP 085, CEP 087, CEP 120, CEP 350, CEP 404, and CEP 423) were isolated from soil samples or nondipteran hosts collected from areas in Argentina where Ae. aegypti is distributed. Bioassays were performed with four conidial concentrations plus a control of each fungal strain to determine the lethal concentrations (LC50/LC90), the median survival times (ST50), the mean percentage of the surviving individuals, and the mean percentage of mycotized cadavers. The strains were able to infect and kill adult Ae. aegypti. Significant differences were found among the LC50 values, with CEP 423 as the most virulent strain with the lowest LC50 (2.4 × 106 conidia/ml). At 1 × 107 conidia/ml: no significant differences were found in the Kaplan–Meier survival functions among the strains; the ST50 ranged from 5 (CEP 085) to 8 d (CEP 350); and the mean percentage of the surviving adults was between 13.3 (CEP 085, CEP 350 and CEP 423) and 46.7% (CEP 087). Significant differences were also found among strains in the mean percentage of cadavers with fungal sporulation. Strain CEP 423 produced the highest percentage of mycotized adults (70%). The concentration of the inoculum significantly affected the survival of individuals and the percentage of mycotized cadavers within each strain. Metarhizium anisopliae s.l. CEP 423 was selected as the most promising candidate for further research aiming to develop a mycoinsecticide against Ae. aegypti.

A survey of bacterial, fungal and plant metabolites against Aedes aegypti (Diptera: Culicidae), the vector of yellow and dengue fevers and Zika virus

Aedes aegypti L. is the major vector of the arboviruses responsible for dengue fever, one of the most devastating human diseases. Some bacterial, fungal and plant metabolites belonging to different chemical subgroups, including Amaryllidaceae alkaloids, anthracenes, azoxymethoxytetrahydropyrans, cytochalasans, 2,5-diketopiperazines, isochromanones, naphthoquinones, organic small acids and their methyl esters, sterols and terpenes including sesquiterpenes and diterpenes, were tested for their larvicidal and adulticidal activity against Ae. aegypti. Out of 23 compounds tested, gliotoxin exhibited mosquitocidal activity in both bioassays with an LC50 value of 0.0257 ± 0.001 µg/µL against 1st instar Ae. aegypti and LD50 value of 2.79 ± 0.1197 µg/mosquito against adult female Ae. aegypti. 2-Methoxy-1,4-naphthoquinone and cytochalasin A showed LC50 values of 0.0851 ± 0.0012 µg/µL and 0.0854 ± 0.0019 µg/µL, respectively, against Ae. aegypti larvae. In adult bioassays, fusaric acid (LD50= 0.8349 ± 0.0118 µg/mosquito), 3-nitropropionic acid (LD50 = 1.6641 ± 0.0494 µg/mosquito) and α-costic acid (LD50 = 2.547 ± 0.0835 µg/mosquito) exhibited adulticidal activity. Results from the current study confirm that compounds belonging to cytochalsin, diketopiperazine, naphthoquinone and low molecular weight organic acid groups are active and may stimulate further SAR investigations.

Toxicity of Compounds Isolated from White Snakeroot (Ageratina altissima) to Adult and Larval Yellow Fever Mosquitoes (Aedes aegypti)

Botanicals have been the source for several classes of pesticides for mosquitoes. However, increasing resistance to these products and reduced numbers of choices necessitate the search for new active ingredients. Ageratina altissima (L.) King & H. Rob. or white snakeroot, is found throughout the eastern United States and contains known toxic compounds. We examine chromenes (benzopyrans) and benzofurans isolated from this plant for larvicidal and adulticidal activity against the dengue vector Aedes aegypti L. Initial activity identified several compounds that were effective against either larvae or adults. Interestingly, only two compounds were effective against both larva and adults. Dose curves were constructed from further testing of these active compounds to allow comparative ranking of efficacy. We identified dehydrotremetone as the most effective larvicide (0.03 ± 0.001 ng/μL) and 6-acetyl-7-methoxy-2,2-dimethylchromene as the most effective adulticide (1.17 ± 0.31 μg/org) although other compounds were also active. This study provides additional useful data for evaluation of chromenes and benzofurans as possible mosquiticidal agents.

Preparative Capillary GC for Characterization of Five Dracocephalum Essential Oils from Mongolia, and their Mosquito Larvicidal Activity

The chemical composition and mosquito larvicidal and adulticidal activity of five essential oils (EOs), Dracocephalum ruyschiana L. (DR), D. foetidum Bunge (DF), D. moldavica L. (DM), D. fruticulosum Steph. ex Willd. (DFr) and D. peregrinum L. (DP) were evaluated. Simultaneous GC-FID and GC-MS analyses revealed in the EOs of DR, DF and DM an unidentified compound (1) ([M+122], 5.4%, 57.9% and 74.0%, respectively). Therefore, we aimed to isolate compound 1 using Preparative Capillary GC (PCGC) connected to a Preparative Fraction Collector (PFC) system. Structure determination of 1 was determined by 1H- and 13C-NMR as p-mentha-1,8-dien-10-al (1, limonen-10-al). Other detected major constituents were thymol (34.0%) and carvacrol (6.1%) in DR; limonene (28.8%) in DF; cis-chrysanthenol acetate (29.1%) and trans-verbenol (5.0%) in DFr; and linalool (17.9%), trans-β-bergamotene (7.9%), (E)-nerolidol (7.7%) and eugenol (5.5%) in DP. The DFr, DP, DR and DM EOs produced 100% mortality to 1st instar larvae of Aedes aegypti L. at 250 ppm and DR and DM EO exhibited the strongest activity and killed 100% 1st instar larvae at 62.5 ppm. No adulticidal activity was observed against female Ae. aegypti. In the scope of the present study, for the first time isolation of limonen-10-al (1) from DR, DM, and DP EOs and larvicidal activity of five Dracocephalum EOs were reported.