Cartography of odor chemicals in the dengue vector mosquito (Aedes aegypti L., Diptera/Culicidae)

Abstract

This study was aimed to identify the chemical compounds of Aedes aegypti that can be potentially used to develop pheromone-based vector control methods. In this study, we compared the chemical compounds collected from the organs of mosquitoes at different developmental stages in the life cycle. We also compared the composition and amount of extracts from the different tissues of male and female adult mosquito. Interestingly, we found large amount of C17-C20 ethyl and methyl esters in the wings of female and antennae of male mosquito. We also found that isopropyl esters, dodelactone, octadecenoic acid and medium-chain fatty acid increase drastically during the late larval stage (L4). Old adult mosquitoes showed remarkable increase in production of C16:1 and C18:1 methyl esters, as a first example of chemical signatures specifically associated with aging in the animals. This knowledge may open the ground to find new behaviorally-important molecules with the ability to control Aedes specifically.

Figure 1

Sex and tissue comparison analysis of odor chemicals in hexane extracts from sexually mature adults in the Dengue fever mosquito, Ae. aegypti. Total ion chromatograms (TICs) of hexane extracts of female and male antennae, legs, head, thorax, abdomen, wings, accessory glands and ovaries, respectively, are given in Supplementary Material 1. To identify the chemicals, mass spectra are given in Supplementary Material 2. C₅H₁₀O₂: butanoic acid, 3-methyl (tR 14.02); C₁₃H₂₆O₂: dodecanoic acid methyl ester (tR 15.32); C₁₅H₃₀O₂: methyl tetradecanoate (tR 17.49), C₁₇H₃₄O₂: hexadecanoic acid methyl ester (tR 19.59); C₁₇H₃₂O₂: (Z)-9-hexadecenoic acid methyl ester (tR 19.83); C₁₉H₃₆O₂: isopropyl-9-hexadecenoate (tR 20.02); C₁₈H₃₄O₂: ethyl 9-hexadecenoate (tR 20.15); C₁₉H₃₈O₂: methyl stearate (tR 21.30); C₁₉H₃₆O₂: 11-octadecenoic acid methyl ester (tR 21.47); C₂₁H₄₀O₂: isopropyl 9-octadecenoate (tR 21.72); C₂₀H₃₈O₂: ethyl oleate (tR 21.86); C₁₉H₃₄O₂: 8,11-octadecadienoic acid methyl ester (tR 21.94); C₂₁H₃₈O₂: isopropyl linoleate (tR 22.11); C₁₉H₃₂O₂: (Z,Z,Z)-9,12,15-octadecatrienoic acid methyl ester (tR 22.41). Statistical differences (SPSS) are shown with asterisks (*P < 0.05; **P < 0.01; ***P < 0.001).

Figure 2

Developmental stage comparison analysis of odor chemicals in hexane extracts from Ae. aegypti eggs, larvae (L1-L4) and nymphs. Total ion chromatograms (TICs) of all various developmental stages and mass spectra are given in Supplementary Material 3. C₅H₁₀O₂: butanoic acid 3-methyl (tR 14.02); C₁₉H₃₆O₂: i-propyl 9-hexadecenoate (tR 20.02); C₁₂H₂₂O₂: dodelactone (tR 21.00); C₂₁H₄₀O₂: isopropyl 9-octadecenoate (tR 21.72); C₁₂H₂₄O₂: dodecanoic acid (tR 22.00); C₁₂H₂₂O₂: (Z)-5-dodecenoic acid (tR 22.30); C₁₃H₂₆O₂: tridecanoic acid (tR 22.45); C₁₄H₂₈O₂: tetradecanoic acid isomers (tR 23.28 & 23.64); C₁₄H₂₆O₂: myristoleic acid (tR 23.89); C₁₅H₃₀O₂: pentadecanoic acid (tR 24.07). 1*–4*: unknown chemicals (NIST). Statistical differences (SPSS) are shown with asterisks (*P < 0.05; **P < 0.01; ***P < 0.001).

Figure 3

Age comparison analysis of odor chemicals in hexane extracts from Ae. aegypti nymphs and young adults of both sexes. Total ion chromatograms (TICs) and mass spectra are given in Supplementary Materials 3 & 4. C₁₇H₃₄O₂: hexadecanoic acid methyl ester (tR 19.59); C₁₇H₃₂O₂: (Z)-9-hexadecenoic acid methyl ester (tR 19.83); C₁₉H₃₆O₂: i-propyl 9-hexadecenoate (tR 20.02); 5*: unknown chemical (NIST). Statistical differences (SPSS) are shown with asterisks (*P < 0.05; **P < 0.01; ***P < 0.001).

Figure 4

Chemical identification of elder-specific odor chemicals in the dengue fever mosquito, Ae. aegypti. Total ion chromatograms (TICs) of young (one-day-old, sexually immature and unmated) and old (>five-days-old, mated and laid eggs) adult mosquitoes (hexane extracts) and mass spectra are given in Supplementary Material 4. C₁₃H₂₆O₂: dodecanoic acid methyl ester (tR 15.32); C₁₅H₃₀O₂: methyl tetradecanoate (tR 17.49); C₁₅H₂₈O₂: methyl myristoleate isomers (tR 17.74 & 17.87); C₁₇H₃₄O₂: hexadecanoic acid methyl ester (tR 19.59); C₁₇H₃₂O₂: (Z)-9-hexadecenoic acid methyl ester (tR 19.83); C₁₉H₃₆O₂: isopropyl-9 hexadecenoate (tR 20.02); C₁₉H₃₈O₂: methyl stearate (tR 21.30); C₁₉H₃₆O₂: 11-octadecenoic acid methyl ester (tR 21.47); C₁₉H₃₄O₂: (Z,Z)-9,12-octadecadienoic acid (tR 21.94); C₁₉H₃₂O₂: (Z,Z,Z)-9,12,15-octadecatrienoic acid methyl ester (tR 22.41). Statistical differences (SPSS) are shown with asterisks (*P < 0.05; **P < 0.01; ***P < 0.001).

Figure 5

Cartography of volatile odorant chemicals (VOCs) in Ae. aegypti mosquito. Yellow* means concentration more than 1.0 µg/l. Green Ѵ means concentration less than 1.0 µg/l. Grey means trace amounts (almost none). Ant: Antennae, Hd: Head, Tho: Thorax, Wgs: Wings, Abd: Abdomen, Leg: Legs, Ov: Ovaries, AG: Accessory gland, Bod: Body, f: female, m: male; E: Eggs, L1-L4: L1 to L4 larval stages, N: Nymphs, A: Adults, OA: Old Adults (post-mating).

Figure 6

Cartography of odor chemicals in Ae. aegypti body. (A) Female, (B) Male. C₅H₁₀O₂: butanoic acid 3-methyl; C₁₅H₃₀O₂: methyl tetradecanoate; C₁₇H₃₂O₂: (Z)-9-hexadecenoic acid methyl ester; C₁₇H₃₄O₂: hexadecanoic acid methyl ester; C₁₈H₃₄O₂: ethyl 9-hexadecenoate; C₁₉H₃₂O₂: (Z,Z,Z)-9,12,15-octadecatrienoic acid methyl ester; C₁₉H₃₄O₂: 8,11-octadecadienoic acid methyl ester; C₁₉H₃₆O₂: isopropyl-9-hexadecenoate; C₁₉H₃₆O₂: 11-octadecenoic acid methyl ester; C₁₉H₃₈O₂: methyl stearate; C₂₀H₃₈O₂: ethyl oleate. Higher concentration of chemical in a specific tissue is shown in bold. In green shows specific chemicals detected in higher amounts in female wings (see A) and male antennae (see B), respectively. In orange shows specific chemicals detected in higher amounts not only in female thorax (see A) but also in male and female legs (see A & B), respectively.