Author
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Byers, John |
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Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/7/2006 Publication Date: 10/1/2006 Citation: Byers, J.A. 2006. Production and predator-induced release of volatile chemicals by the plant bug Lygus hesperus. Journal of Chemical Ecology 32:2205-2218. Interpretive Summary: Both sexes of adult western tarnished plant bug, Lygus hesperus Knight (Heteroptera: Miridae), released three defensive compounds in relatively large amounts when attacked by ants (Pogonomyrmex rugosus or Solenopsis xyloni) or when grabbed by forceps as determined by solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). The released defensive compounds, expressed as a percentage of maximum peak area, were hexyl butyrate (female: 100%, male: 69%), (E)-2-hexenyl butyrate (female: 4%, male: 6%) and (E)-4-oxo-2-hexenal (female: 25%, male: 22%). Both ant species were repelled by defensive discharges (confirmed by SPME) when the ants attacked the adults. Sexually mature L. hesperus were individually extracted in pentane to quantify the amounts of hexyl butyrate (14.9 ug/female, 100%; 10.3 ug/male, 69%), (E)-2- hexenyl butyrate (1.2 ug/female, 8%; 0.6 ug/male, 4%) and (E)-4-oxo-2-hexenal (2.7 ug/female, 18%; 3.1 ug/male, 21%). Solvent had to be decanted from the macerated adult within minutes to avoid loss of (E)-4-oxo-2-hexenal. The production of the three major defensive components began soon after eclosion and amounts increased for about 5-10 days with little or no increase thereafter. Additional constituents were cross-correlated with the three major ones yielding many significant positive correlations. A cost of defensive secretion is suggested for females but not for males since heavier females produced slightly more defensive compounds than lighter ones. A new concept termed the initial discharge percentage (IDP) estimates the proportion of defensive amounts initially present that is discharged to defend against predation. The IDP was estimated at about 49% in males and 71% in females, or an average of 60%. Immature first to fifth instars lacked defensive compounds except for small amounts of (E)-2-octenal (less than or equal to 1 ng/nymph) not detected by SPME after molestation nor found in adults. S. xyloni readily attacked nymphs and no repulsion was observed. It is enigmatic that evolution has resulted in nymphs that appear chemically defenseless while adults release large amounts of irritants for repelling ants and possibly other predators that both life stages would have in common. Technical Abstract: Both sexes of adult western tarnished plant bug, Lygus hesperus Knight (Heteroptera: Miridae), released three defensive compounds in relatively large amounts when attacked by ants (Pogonomyrmex rugosus or Solenopsis xyloni) or when grabbed by forceps as determined by solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). The released defensive compounds, expressed as a percentage of maximum peak area, were hexyl butyrate (female: 100%, male: 69%), (E)-2-hexenyl butyrate (female: 4%, male: 6%) and (E)-4-oxo-2-hexenal (female: 25%, male: 22%). Both ant species were repelled by defensive discharges (confirmed by SPME) when the ants attacked the adults. Sexually mature L. hesperus were individually extracted in pentane to quantify the amounts of hexyl butyrate (14.9 ug/female, 100%; 10.3 ug/male, 69%), (E)-2- hexenyl butyrate (1.2 ug/female, 8%; 0.6 ug/male, 4%) and (E)-4-oxo-2-hexenal (2.7 ug/female, 18%; 3.1 ug/male, 21%). Solvent had to be decanted from the macerated adult within minutes to avoid loss of (E)-4-oxo-2-hexenal. The production of the three major defensive components began soon after eclosion and amounts increased for about 5-10 days with little or no increase thereafter. Additional constituents were cross-correlated with the three major ones yielding many significant positive correlations. A cost of defensive secretion is suggested for females but not for males since heavier females produced slightly more defensive compounds than lighter ones. A new concept termed the initial discharge percentage (IDP) estimates the proportion of defensive amounts initially present that is discharged to defend against predation. The IDP was estimated at about 49% in males and 71% in females, or an average of 60%. Immature first to fifth instars lacked defensive compounds except for small amounts of (E)-2-octenal (less than or equal to 1 ng/nymph) not detected by SPME after molestation nor found in adults. S. xyloni readily attacked nymphs and no repulsion was observed. It is enigmatic that evolution has resulted in nymphs that appear chemically defenseless while adults release large amounts of irritants for repelling ants and possibly other predators that both life stages would have in common. |
