Production and predator-induced release of volatile chemicals by the plant bug Lygus hesperus

Both sexes of adult western tarnished plant bug, Lygus hesperus Knight (Heteroptera: Miridae), released three volatile chemicals in relatively large amounts when attacked by ants (Pogonomyrmex rugosus and Solenopsis xyloni) or when grabbed by forceps, as determined by solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). The relative amounts of the volatile compounds, hexyl butyrate, (E)-4-oxo-2-hexenal, and (E)-2-hexenyl butyrate, absorbed by SPME as a percentage of the largest were 100%, 44%, and 4%, respectively, from females, and 83%, 37%, and 3% from males. Both ant species were repelled by the defensive discharges (confirmed by SPME) when the ants attacked L. hesperus adults. Sexually mature L. hesperus were individually extracted in pentane to quantify the mean amounts of hexyl butyrate (14.9 microg/female; 10.3 microg/male), (E)-4-oxo-2-hexenal (2.7 microg/female; 3.1 microg/male), and (E)-2-hexenyl butyrate (1.2 microg/female; 0.6 microg/male). (E)-4-Oxo-2-hexenal was unstable in solvent when in contact with a macerated adult, but relatively stable when the solution was decanted within minutes. The production of the three major volatile components began soon after the emergence of the adult and amounts increased for about 5-10 d with little or no increase thereafter. Minor additional constituents were cross-correlated in many cases with the three major ones. A cost of defensive secretion is suggested for females but not for males, because heavier females produced more volatile compounds than lighter females. The initial discharge percentage, defined as the proportion of volatile compounds initially present that is discharged to defend against predation was estimated at about 50% in males and 70% in females. Newly eclosed adults did not produce volatile chemicals until 2 d after molting.