Fig 1.
Volatiles from overcrowded/starved larval water habitats affect oviposition behavior of An. coluzzii gravid females.
(A) Schematic of oviposition dual choice behavioral assay designed to examine olfactory-driven responses (see Methods for details). Oviposition preference of gravid females to larval water samples with varied treatment by (B) incubating different number of late instars for 72 h, (C) incubating 300 late instars for different time period, and (D) diluting LW sample obtained by incubating 300 late instars for 72 h. Asterisks represent significant OI values different from zero (***, p < 0.001; **, p < 0.01; Wilcoxon signed-rank test, two-sided). Error bar = s.e.m. (n = 17 ~ 36).
Fig 2.
DMDS, DMTS and sulcatone are significant volatile components in the headspace of larval water samples.
Partial chromatograms are shown for volatile samples taken from larval water (LW), control water (CW), and standard DMDS (10-7 M), DMTS (10−8 M) and sulcatone (10−8 M) using SPME headspace analysis coupled with gas chromatography–mass spectrometry. Peaks for DMDS, DMTS and sulcatone are marked with red arrows. No additional LW specific compounds were detected beyond the retention time of sulcatone. Large peaks with retention times of approximately 3.2, 4.3 and 5.8 min represent impurities possibly introduced during sample preparations and/or chemical analyses, which are present in all samples including LW and CW.
Fig 3.
Oviposition behavior of An. coluzzii gravid females is negatively affected by DMDS, DMTS and sulcatone.
An. coluzzii gravid females were allowed oviposit between control water and DMDS, DMTS and sulcatone with serial dilutions. Asterisks represent significant OI value different from zero (**, p < 0.01; *, p < 0.05; Wilcoxon signed-rank test, two-sided). Error bar = s.e.m. (n = 14 ~ 35).
Fig 4.
Chemosensory appendages of gravid An. coluzzii electrophysiologically respond to DMDS, DMTS and sulcatone.
(A) EAG, (B) EPG and (C) ELG responses (each chemosensory organ is highlighted in red in a schematic diagram of mosquito head) are expressed as response difference to solvent control (oil) of An. coluzzii females to DMDS, DMTS and sulcatone. Y axis represents response amplitude subtracted by control values and X axis represents log transformed molar concentration. Asterisks represent significant response amplitude different from zero (***, p < 0.001; **, p < 0.01; *, p < 0.05; one sample t-test, one-sided). Error bar = s.e.m. (n = 7).
Fig 5.
Neurons in capitate peg sensillum of maxillary palp are activated by DMDS, DMTS and sulcatone.
Electrophysiological activities of (A) cpA, (B) cpB and (C) cpC neurons in capitate peg sensillum (highlighted in a red box; picture modified from a previous study [35]) of maxillary palp in gravid An. coluzzii females are identified by spike amplitudes, and changes in spike frequency are quantified to characterize individual neuronal response to varying concentrations of DMDS, DMTS and sulcatone. Y axis represents response spike number subtracted by control response values (DMSO) and X axis represents log transformed molar concentration of DMDS, DMTS and sulcatone. Asterisks represent significant response amplitude different from zero (***, p < 0.001; **, p < 0.01; *, p < 0.05; one sample t-test, one-sided). Error bar = s.e.m. (n = 7~10).