Sex- and Metamorphosis-Related Changes in the Cuticular Lipid Profile of Galleria mellonella Pupae and Adults

Abstract

The majority of insects reproduce sexually. Among the many factors involved in controlling the reproductive process, cuticular lipids play an important role as unique chemical signatures of species, developmental stage, and sex, and participate in mate recognition. An understanding of the sex- and metamorphosis-related fluctuations in the cuticular lipid profiles of harmful insects is necessary to hamper their reproductive process. A GC/MS analysis of the cuticular lipids of the beehive pest Galleria mellonella Linnaeus (Lepidoptera: Pyralidae) revealed 11 FFAs in the male pupae (C8:0, C9:0, C14:0, C15:0, C16:1, C16:0, C17:0, C18:1, C18:0, C20:1, and C21:1) together with another two in the females (C10:0 and C17:1). As metamorphosis progressed, some FFAs disappeared from the pupal cuticle (C8:0 and C17:0 in both sexes, and C10:0, C17:1, and C20:1 only in female pupae) and the levels of the others changed. In adult virgin males and females, C8:0, C17:1, and C17:0 reappeared and two FFAs absent in pupae (C6:0 and C11:0) appeared. In virgin males, C13:0 also appeared (absent in pupae). Copulation resulted in the disappearance of C13:0 and C17:1, decreased the concentrations of C9:0, C11:0, C18:1, and C18:0, and elevated the amounts of C14:0, C16:1, and C16:0 in mated males. In mated females, the concentrations of C11:0, C14:0, C15:0, C16:0, C17:1, and C18:1 increased while C18:1 decreased. Copulation reduced cholesterol levels in mated females, and increased those in males.

Keywords: GC/MS; Galleria mellonella; cholesterol; copulation; cuticular free fatty acids; metamorphosis.

Figure 1

The total ion current (TIC) of fatty acids (TMSs) of the dichloromethane extract from the Galleria mellonella female pupae (A)—1-day-old (1dP-F); (B)—3-day-old (3dP-F); (C)—6-day-old (6dP-F). IS—internal standard (19-methylarachidic acid); fatty acids and molecular ions: octanoic acid (C8:0, m/z = 216), nonanoic acid (C9:0, m/z = 230), tetradecanoic acid (C14:0, m/z = 300), pentadecanoic acid (C15:0, m/z = 314), hexadecenoic acid (C16:1, m/z = 326), hexadecanoic acid (C16:0, m/z = 328), heptadecenoic acid (C17:1, m/z = 340), heptadecanoic acid (C17:0, m/z = 342), octadecenoic acid (C18:1, m/z = 354), octadecanoic acid (C18:0, m/z = 356), eicosenoic acid (C20:1, m/z = 382), and heneicosenoic acid (C21:1, m/z = 396). The mass spectra of the tested TMSs revealed the presence of the ions: M⁺ (molecular ion), [M-15]⁺, and fragment ions at m/z 117, 129, 132. The contents were calculated by comparing the relative peak areas with the IS peak area.

Figure 2

The total ion current (TIC) of fatty acids (TMSs) of the dichloromethane extract from the Galleria mellonella male pupae (A)—1-day-old (1dP-M); (B)—3-day-old (3dP-M); (C)—6-day-old (6dP-M). IS—internal standard (19-methylarachidic acid); fatty acids and molecular ions: octanoic acid (C8:0, m/z = 216), nonanoic acid (C9:0, m/z = 230), decanoic acid (C10:0, m/z = 244), tetradecanoic acid (C14:0, m/z = 300), pentadecanoic acid (C15:0, m/z = 314), hexadecenoic acid (C16:1, m/z = 326), hexadecanoic acid (C16:0, m/z = 328), heptadecenoic acid (C17:1, m/z = 340), heptadecanoic acid (C17:0, m/z = 342), octadecenoic acid (C18:1, m/z = 354), octadecanoic acid (C18:0, m/z = 356), eicosenoic acid (C20:1, m/z = 382), and 21-heneicosenoic acid (C21:1, m/z = 396). Further explanations are given in Figure 1.

Figure 3

The total ion current (TIC) of fatty acids (TMSs) of the dichloromethane extract from the Galleria mellonella adults (A)—virgin male (3dA-MV); (B)—male after copulation (3dA-MC). IS—internal standard (19-methylarachidic acid); fatty acids and molecular ions: hexanoic acid (C6:0, m/z = 188), octanoic acid (C8:0, m/z = 216), nonanoic acid (C9:0, m/z = 230), undecanoic acid (C11:0, m/z = 258), tridecanoic acid (C13:0, m/z = 286), tetradecanoic acid (C14:0, m/z = 300), pentadecanoic acid (C15:0, m/z = 314), hexadecenoic acid (C16:1, m/z = 326), hexadecanoic acid (C16:0, m/z = 328), heptadecenoic acid (C17:1, m/z = 340), heptadecanoic acid (C17:0, m/z = 342), octadecenoic acid (C18:1, m/z = 354), octadecanoic acid (C18:0, m/z = 356), eicosenoic acid (C20:1, m/z = 382), heneicosenoic acid (C21:1, m/z = 396), tetracosanoic acid (C24:0, m/z = 440), and 23-hexacosanoic acid (C26:0, m/z = 468). Further explanations are given in Figure 1.

Figure 4

The total ion current (TIC) of fatty acids (TMSs) of the dichloromethane extract from the Galleria mellonella adults (A)—virgin female (3dA-FV); (B)—female after copulation (3dA-FC). IS—internal standard (19-methylarachidic acid); fatty acids and molecular ions: hexanoic acid (C6:0, m/z = 188), octanoic acid (C8:0, m/z = 216), nonanoic acid (C9:0, m/z = 230), undecanoic acid (C11:0, m/z = 258), tridecanoic acid (C13:0, m/z = 286), tetradecanoic acid (C14:0, m/z = 300), pentadecanoic acid (C15:0, m/z = 314), hexadecenoic acid (C16:1, m/z = 326), hexadecanoic acid (C16:0, m/z = 328), heptadecenoic acid (C17:1, m/z = 340), heptadecanoic acid (C17:0, m/z = 342), octadecenoic acid (C18:1, m/z = 354), octadecanoic acid (C18:0, m/z = 356), eicosenoic acid (C20:1, m/z = 382), heneicosenoic acid (C21:1, m/z = 396), tetracosanoic acid (C24:0, m/z = 440), and 23-hexacosanoic acid (C26:0, m/z = 468). Further explanations are given in Figure 1.