Identification of volatile components from oviposition and non-oviposition plants of Gasterophilus pecorum (Diptera: Gasterophilidae)
Volatile contents of S. caucasica shoots during the stages of oviposition by G. pecorum
Overall, 60 volatile compounds were identified in S. caucasica shoots during the preoviposition (I), oviposition (II), and postoviposition (III) stages of G. pecorum. These comprised 16 aldehydes, 14 ketones, 12 esters, 9 alcohols, 3 alkanes, 3 aromatic hydrocarbons, 1 acid, 1 ether, and 1 other. Among them, 35 volatiles were identified in I-L, 36 in II-L, and 37 in III-L. In addition, 18 volatiles were common to I-L, II-L, and III-L; 5 to I-L and II-L; 5 to II-L and III-L; and 2 to I-L and III-L. Ten volatiles were unique to I-L, 8 to II-L, and 12 to III-L (Table 1). The main chemical classes of I-L, II-L, and III-L were alcohols, esters, and others; alcohols and others; and alcohols and esters, respectively (Fig. 1).
Table 1 Volatiles detected from shoots of Stipa caucasica during preoviposition, oviposition, and postoviposition of Gasterophilus pecorum.
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Figure 1
Volatiles classes from shoots of Stipa caucasica during preoviposition, oviposition, and postoviposition of Gasterophilus pecorum. I-L, II-L, and III-L represent Stipa caucasica shoots during the preoviposition, oviposition, and postoviposition stages of Gasterophilus pecorum. (A) alcohols, (B) esters, (C) aldehydes, (D) ketones, (E) others, (F) acids, (G) alkanes, (H) aromatic hydrocarbons, and (I) ethers. Data are mean (n = 3) ± SE. Different letters indicate significant differences at p 0.05) (Fig. 1A). Of the alcohols, 3-hexen-1-ol,(Z)- had the highest relative contents, 25.68%, 55.65%, and 32.35% in I-L, II-L, and III-L, respectively, with no significant differences among these three (P > 0.05). The relative content of 1-hexanol was higher in II-L (1.52%) than in III-L (1.01%) (P = 0.002) or I-L (0.89%) (P = 0.001), whereas III-L and I-L showed no significant difference (P > 0.05). The relative contents of the other volatile alcohols were less than 0.8% (Table 1).
Twelve esters were identified from the three stages of S. caucasica. Among them, three, i.e., acetic acid hexyl ester, ethyl acetate, and acetic acid phenylmethyl ester, were common to all three stages; and four, i.e., 3-cyclohexen-1-ol,acetate, 2(3H)-furanone,5-ethyldihydro-, 3-hexen-1-ol,formate,(Z)-, and acetic acid pentyl ester, were common to two of the three stages. The relative contents of esters were lower in II-L (3.16%) than in III-L (40.61%) or I-L (27.81%) (P = 0.000; P = 0.000), whereas there was no significant difference between III-L and I-L (P > 0.05) (Fig. 1B). The relative contents of acetic acid hexyl ester in II-L (1.47%) and III-L (1.14%) were not significantly different (P > 0.05), but were higher in both than in I-L (0.52%) (P = 0.001 and 0.005, respectively). The relative contents of 3-hexen-1-ol,acetate,(Z)- (24.8%), a specific volatile of I-L, and 3-hexen-1-ol,acetate(E)- (38.7%), which was specific to III-L, were highest in esters in stages specifically containing them. The relative content of propanoic acid,2-methyl-,3-hydroxy-2,4,4-trimethylpentyl ester, which was detected only in I-L, was 1.12%, whereas those of the other volatiles in esters were lower than 0.8% (Table 1).
Sixteen aldehydes were identified from the three stages of S. caucasica. Among them, seven, i.e., hexanal, nonanal, decanal, heptanal, undecanal, 2-octenal, (E)-, and 2-heptenal,(Z)-, were common to all three stages; and two, i.e., 3-hexenal and 2,4-hexadienal, (E,E)-, were common to two of the three stages. The relative contents of aldehydes in I-L, II-L, and III-L were 10.83%, 6.84%, and 9.9%, and those of hexanal were 0.62%, 2.38%, and 1.16%, respectively; none of these differences was significant (P > 0.05) (Fig. 1C). The relative contents of nonanal in I-L (1.45%) and II-L (1.9%) did not differ significantly (P > 0.05), and both were higher than that in III-L (0.96%) (P > 0.05 and P = 0.018, respectively). The relative content of decanal was higher in II-L (1.20%) than in I-L (0.78%) (P = 0.043) or III-L (0.65%) (P = 0.016), but those in I-L and III-L did not differ significantly (P > 0.05). The following two volatiles were present in two of the three stages: 3-hexenal, with higher content in I-L (7.10%) than in III-L (5.03%) (P > 0.05); and 2,4-hexadienal,(E,E)-, with content higher in II-L (0.3%) than in III-L (0.22%) (P = 0.00). Benzaldehyde was specific to III-L (0.99%), with the relative contents of other volatile aldehydes 0.05), with no significant difference between II-L and III-L (P > 0.05) (Fig. 1D). The content of 2(5H)-Furanone,5-ethyl- was specific to II-L (2.38%), and the relative contents of the other ketones were 0.05), and both were higher than those for III-L (12.9%) (P = 0.017 and P > 0.05, respectively) (Fig. 1E). The relative content of acetic acid, the only volatile in the class of acids, was lower in III-L (0.61%) than in II-L (3.36%) or I-L (2.14%) (P = 0.022 and P > 0.05, respectively); there was no significant difference between the latter two (P > 0.05). The relative contents of alkanes, aromatic hydrocarbons, and ethers were less than 0.22% (Fig. 1G–I). These included three alkanes, one in I-L and two each in II-L and III-L; three aromatic hydrocarbons, one of them specific to each stage; and one ether, which was not found in III-L (Table 1).
The five volatile compounds with the highest relative contents, in order, during the three stages of S. caucasica were as follows: I-L, caprolactam (30.66%) > 3-hexen-1-ol,(Z)- (25.68%) > 3-hexen-1-ol,acetate,(Z)- (24.8%) > 3-hexenal (7.1%) > acetic acid (2.14%); II-L, 3-hexen-1-ol,(Z)- (55.65%) > caprolactam (22.68%) > acetic acid (3.36%) > hexanal (2.38%) = 2(5H)-furanone,5-ethyl- (2.38%); III-L, 3-hexen-1-ol,acetate,(E)- (38.7%) > 3-hexen-1-ol,(Z)- (32.35%) > caprolactam (12.9%) > 3-hexenal (5.03%) > hexanal (1.16%) (Table 1). A total of eight volatiles were detected: two (i.e., 3-hexen-1-ol,(Z)- and caprolactam) were common to the three stages, and three (i.e., acetic acid, 3-hexenal, and hexanal) to two of the three stages. Finally, 2(5H)-furanone,5-ethyl- was in the top 5 volatile compounds of only II-L.
Relative contents of volatiles in three plant species during the oviposition stage of G. pecorum
During the oviposition stage of G. pecorum, a total of 60 volatiles were identified in S. orientalis (II-D), S. caucasica (II-L), and C. latens (II-T). These comprised 18 esters, 13 aldehydes, 11 alcohols, 10 ketones, 2 alkanes, 2 aromatic hydrocarbons, 1 acid, 1 alkene, 1 ether, and 1 other. Of these, 35 were identified in II-D, 36 in II-L, and 27 in II-T. In addition, 11 were common to II-D, II-L, and II-T, 14 to II-D and II-L, and 2 to II-L and II-T; 10 were unique to II-D, 9 to II-L, and 14 to II-T (Table 2). The main chemical classes of II-D and II-L were alcohols and others, and those of II-T were alcohols, esters, and others (Fig. 2).
Table 2 Volatiles detected from shoots of three plant species during oviposition of Gasterophilus pecorum.
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Figure 2
Volatiles classes from shoots of three plant species during oviposition of Gasterophilus pecorum. II-D, II-L, and II-T represent shoots of Stipa orientalis, Stipa caucasica, and Ceratoides latens during the oviposition stage of Gasterophilus pecorum. (A) alcohols, (B) esters, (C) aldehydes, (D) ketones, (E) others, (F) acids, (G) alkanes, (H) aromatic hydrocarbons, (I) ethers, and (J) alkenes. Data are mean (n = 3) ± SE. Different letters indicate significant differences at p 0.05) (Fig. 2A). The relative content of 3-hexen-1-ol,(Z)- was lower in II-T (14.28%) than in II-L (55.65%) or II-D (44.64%) (P = 0.002 and 0.008), but there was not significant difference between II-L and II-D (P > 0.05). The relative contents of 1-hexanol and 2-hexen-1-ol,(E)- in II-D, II-L, and II-T were 1.67%, 1.52%, 2.79%, and 0.72%, and 0.59% and 2.66%, respectively; these differences were not significant (P > 0.05). Finally, 3-hexen-1-ol was specific to II-D (1.57%), and the relative contents of other alcohols were 0.05) (Fig. 2B). The relative content of acetic acid hexyl ester in II-D, II-L, and II-T was 0.4%, 1.47%, and 4.25%, respectively; these differences were not significant (P > 0.05). The relative content of 2(3H)-furanone, 5-ethyldihydro- was higher in II-T (0.71%) than in II-D (0.27%) or II-L (0.26%) (P = 0.000; P = 0.000), but II-D and II-L were not significantly different (P > 0.05). Both 3-hexen-1-ol,acetate,(Z)- (13.13%) and propanoic acid,2-methyl-,3-hydroxy-2,4,4-trimethylpentyl ester (1.07%) were unique to II-D, and benzoic acid methyl ester (1.88%), methyl salicylate (2.52%), and cis-3-hexenyl isovalerate (8.45%) were all unique to II-T. The relative contents of other esters were 0.05) (Fig. 2C). The relative contents of hexanal, nonanal, decanal, and heptanal were 0.25–2.38% and were higher in II-L than in II-D or II-T, although the differences were not significant (P > 0.05). Finally, 3-hexenal (6.57%) was unique to II-D, and benzaldehyde (0.94%) to II-T. The relative contents of other aldehydes were 0.05) (Fig. 2D). Five ketones, i.e., 5-hepten-2-one,6-methyl-, 2(3H)-furanone,dihydro-5-methyl-, 2-hexanone,4-methyl-, 2-undecanone,6,10-dimethyl-, and acetophenone, were common to II-D and II-L, and 2(5H)-furanone,5-ethyl- (2.38%) was unique to II-L. The relative contents of other ketones were 0.05) (Fig. 2E). Acetic acid was the only substance in the class ‘acids,’ and its relative content was lower in II-D (1.44%) than in II-T (3.62%) (P = 0.046) or II-L (3.36%) (P > 0.05); contents in II-T and II-L did not differ significantly (P > 0.05). The only alkene, 1,3,6-Octatriene,3,7-dimethyl-, was unique to II-T (12.67%). The relative contents of other alkanes and ethers were caprolactam (21.76%) > 3-hexen-1-ol,acetate,(Z)- (13.13%) > 3-hexenal (6.57%) > 1-hexanol (1.67%); II-L, 3-hexen-1-ol,(Z)- (55.65%) > caprolactam (22.68%) > acetic acid (3.36%) > hexanal (2.38%) = 2(5H)-furanone,5-ethyl- (2.38%); II-T, caprolactam (34.2%) > 3-hexen-1-ol,(Z)- (14.28%) > 1,3,6-octatriene,3,7-dimethyl- (12.67%) > cis-3-hexenyl isovalerate (8.45%) > acetic acid hexyl ester (4.25%) (Table 2). Eleven volatiles were included: two (3-hexen-1-ol,(Z)- and caprolactam) were common to all three plant species; the other nine were in the top five of only one species.
Relative contents of volatiles from S. caucasica in different growth periods
From S. caucasica at the early, flourishing, and late growth periods (GP1, GP2, and GP3, respectively), a total of 69 volatile compounds were identified. These comprised 17 ketones, 13 aldehydes, 11 esters, 10 alcohols, 4 alkanes, 4 aromatic hydrocarbons, 2 acids, 2 alkenes, 1 ether, and 5 others. Of these, 35 were found in GP1, 36 in GP2, and 40 in GP3. In addition, 11 were common to all three stages, 10 to both GP2 and GP3, 6 to both GP1 and GP2, and 4 to both GP1 and GP3; 14 were unique to GP1, 9 to GP2, and 15 to GP3 (Table 3). The main chemical classes of GP1 and GP2 were alcohols and others, and those of GP3 were esters and others (Fig. 3).
Table 3 Volatiles detected from shoots of Stipa caucasica during its different growth periods.
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Figure 3
Volatiles classes from shoots of Stipa caucasica during its different growth periods. GP1, GP2, and GP3 represent Stipa caucasica shoots during the early, flourishing, and late growth periods, respectively. Note that GP2 was actually the same sample as II-L in Figs. 1 and 2. Thus, the three groups had a total of seven rather than nine samples. (A) alcohols, (B) esters, (C) aldehydes, (D) ketones, (E) others, (F) acids, (G) alkanes, (H) aromatic hydrocarbons, (I) ethers, and (J) alkenes. Data are mean (n = 3) ± SE. Different letters indicate significant differences at p 0.05). The 3-hexen-1-ol,(Z)- content, which was the highest among all alcohols, was lower in GP3 (15.42%) than in GP1 (49.5%) or GP2 (55.65%) (P = 0.005 and 0.002, respectively); the latter two did not differ significantly (P > 0.05). The relative content of 1-hexanol was lower in GP3 (0.59%) than in GP1 (1.98%) or GP2 (1.52%) (P = 0.001 and 0.007, respectively); the latter two were not significantly different (P > 0.05). The relative contents of other alcohols were 0.05) (Fig. 3B). The relative content of acetic acid hexyl ester was higher in GP2 (1.47%) than in GP1 (0.52%) (P = 0.022) or GP3 (0.98%) (P > 0.05), with no significant difference between GP1 and GP3 (P > 0.05). Propanoic acid,2-methyl-,3-hydroxy-2,4,4-trimethylpentyl ester (1.48%) was unique to GP1, and 3-hexen-1-ol,acetate,(Z)- (28.42%) to GP3. The relative contents of other esters were 0.05) (Fig. 3E). The relative contents of the remaining four ‘others’ were 0.05) (Fig. 3C). The relative contents of hexanal and decanal decreased with growth period from 4.77% and 1.38% to 1.51% and 1.06%, respectively; but there were no significant differences between periods (P > 0.05). Six volatiles were common to two of the three periods. There were no significant differences between the relative contents of 3-hexenal in GP3 (6.13%) and in GP1 (5.50%) (P > 0.05) or between those of nonanal in GP2 (1.90%) and GP3 (1.43%) (P > 0.05). Finally, 2-hexenal (4.51%) was unique to GP3, and the relative contents of other aldehydes were 0.05) (Fig. 3D). The relative content of 5-hepten-2-one, 6-methyl- was higher in GP1 (0.7%) than in GP3 (0.33%) (P = 0.020), with no significant difference between that in GP2 (0.45%) and that in GP1 or GP3 (both P > 0.05). The relative content of 2-undecanone,6,10-dimethyl- was higher in GP1 (3.12%) than in GP2 (0.14%) (P = 0.05). Finally, 2(5H)-furanone,5-ethyl- (2.38%) was specific to GP2, and the relative contents of other ketones were 0.05) (Fig. 3F). The relative content of acetic acid, which was common to all three periods, was higher in GP2 (3.36%) than in GP3 (0.97%) (P = 0.035), but there was no significant difference between GP1 (1.87%) and GP2 or GP3 (both P > 0.05). The other acid, propanoic acid,2-methyl-,2,2-dimethyl-1- (1%), was specific to GP3 (Table 3).
Four alkanes were identified, and the relative contents of individual alkanes ranged from 0.06% to 0.89%. The relative contents of all alkanes were higher in GP1 (1.56%) than in GP3 (0.15%) (P = 0.022), with no significant difference between GP2 (0.22%) and GP1 or GP3 (both P > 0.05) (Fig. 3G). Two alkenes were found only in GP3; they had a total relative content of 4.76% (Fig. 3J); one, 1,3,6-octatrine,3,7-dimethyl-, accounted for 4.70% of this total. The relative aromatic hydrocarbon and ether contents were caprolactam (19.78%) > 3-hexenal (5.5%) > hexanal (4.77%) > 2-undecanone,6,10-dimethyl- (3.12%); GP2, 3-hexen-1-ol,(Z)- (55.65%) > caprolactam (22.68%) > acetic acid (3.36%) > hexanal (2.38%) = 2(5H)-furanone,5-ethyl-(2.38%); GP3, caprolactam (28.8%) > 3-hexen-1-ol,acetate,(Z)- (28.42%) > 3-hexen-1-ol,(Z)- (15.42%) > 3-hexenal (6.13%) > 1,3,6-octatriene,3,7-dimethyl- (4.70%) (Table 3). Overall, nine volatiles were detected: two (3-hexen-1-ol,(Z)- and caprolactam) were in the top five in all three growth periods, two (3-hexenal and hexanal) in two growth periods, and the other five were in the top five of in only one of the three growth periods. More