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. 2020 Feb 20;10(1):3092.
doi: 10.1038/s41598-020-60056-9.

Analysis of defensive secretion of a milkweed bug Lygaeus equestris by 1D GC-MS and GC×GC-MS: sex differences and host-plant effect

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Analysis of defensive secretion of a milkweed bug Lygaeus equestris by 1D GC-MS and GC×GC-MS: sex differences and host-plant effect

Martina Havlikova et al. Sci Rep. .

Abstract

The composition of defensive secretion produced by metathoracic scent glands was analysed in males and females of the milkweed bug Lygaeus equestris (Heteroptera) using gas chromatography with mass spectrometric detection (GC-MS). The bugs were raised either on cardenolide-containing Adonis vernalis or on control sunflower seeds in order to determine whether the possibility to sequester cardenolides from their host plants would affect the composition of defensive scent-gland secretion. Profiles of the composition of defensive secretions of males and females raised on sunflower were closely similar, with predominant presence of (E)-2-octenal, (E)-2-octen-1-ol, decanal and 3-octen-1-ol acetate. The secretion of bugs raised on A. vernalis was more sexually dimorphic, and some chemicals e.g. (E,E)-2,4-hexadienyl acetate and 2-phenylethyl acetate were dominant in males, but absent in females. Compared to bugs from sunflower, the scent-gland secretion of bugs raised on A. vernalis was characterized by lower overall intensity of the peaks obtained for detected chemicals and by absence of some chemicals that have supposedly antipredatory function ((E)-2-hexenal, (E)-4-oxo-hex-2-enal, 2,4-octadienal). The results suggest that there might be a trade-off between the sequestration of defensive chemicals from host plants and their synthesis in metathoracic scent-glands.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Chromatogram obtained by SPME-GC-MS analysis of the defensive secretion of L. equestris males raised on sunflower seeds on mid-polar Rtx-200 column; identified analytes: (1) 3-hexenal, (2) coeluting decanal, (E)-2-octenal and nonanal, (3) 2,4-octadienal, (4) 3-octen-1-ol acetate, (5) cyclooctanol, (6) (E)-2-decenal, (7) undec-2-enyl acetate.
Figure 2
Figure 2
SPME-GC-MS analysis of the defensive secretion of L. equestris. Comparison of males and females raised on different host plants: toxic A. vernalis and non-toxic sunflower used as a control. Numbering of the peaks corresponds to Table 1.
Figure 3
Figure 3
SPME-GC×GC-MS analysis of the defensive secretion of L. equestris. Comparison of males and females raised either on toxic A. vernalis or the control, non-toxic sunflower seeds. Numbering of the peaks corresponds to Table 2.
Figure 4
Figure 4
Cut-out of the contour plot obtained for the defensive secretion of the males of L. equestris raised on sunflower seeds. Identification of co-eluted compounds.
Figure 5
Figure 5
Cut-out of the contour plot obtained for the defensive secretion of L. equestris males raised on A. vernalis seeds. Identification of co-eluted compounds.
Figure 6
Figure 6
PCA of the composition of defensive secretions in males and females of L. equestris raised on different host plants. The first principal component (PC1) explains 72.91% of variance and the second principal component (PC2) explains 19.92% of variance. Symbols: H(M) males and H(F) females raised on sunflower seeds, A(M) males and A(F) females raised on A. vernalis seeds.
Figure 7
Figure 7
Comparison of the blank, dorsolateral space fluid and scent-gland secretion. SPME-GC-MS analysis of the scent-gland secretion of the male L. equestris raised on sunflower seeds and the blank and the dorsolateral space fluid released by male of L. equestris raised on A. vernalis. Sampling of the secretion was made by compression with the plunger of a syringe, for obtaining the blank this step was omitted.

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