3-hexenylacetate and 4-8-12-trimethyl-1-3-7-11-tridecatetraene

Upon insect herbivory, plants can release blends of volatile organic compounds (VOCs) that modify herbivore and natural enemy behaviour. We have shown recently that cotton, Gossypium hirsutum, emits a blend of defence VOCs that repels the cotton aphid, Aphis gossypii, upon herbivory by this notorious crop pest, including (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). In this study, we investigated changes in the defence VOC profile of G. hirsutum induced by the naturally-occurring plant elicitor cis-jasmone (CJ) and whether these changes modify the behaviour of A. gossypii. In four-arm olfactometer assays, VOCs from untreated plants were significantly attractive (P<0.05), whilst VOCs from CJ-treated plants were significantly repellent (P<0.05). The VOCs induced by CJ appeared to comprise (Z)-3-hexenyl acetate, DMNT, methyl salicylate and TMTT. In quantitative VOC collection studies, sustained release of DMNT and TMTT was observed in CJ-treated plants over a period of five days, with levels becoming statistically significantly higher than for control treated plants on the fifth day in most cases. Despite earlier indications, no statistically significant differences were observed in levels of (Z)-3-hexenyl acetate or methyl salicylate between CJ and control treatments on any day. Furthermore, DMNT and TMTT emissions from CJ-treated plants were further enhanced by subsequent addition of A. gossypii. CJ treatment induced statistically significantly higher DMNT and TMTT expression levels as early as day three, when A. gossypii was present. The results in this study show that CJ can induce the production of A. gossypii-induced VOCs from G. hirsutum, with potential for deployment in novel crop protection strategies.

Topics: Acetates; Alkenes; Animals; Aphids; Cyclopentanes; Gossypium; Herbivory; Molecular Structure; Oxylipins; Salicylates; Stereoisomerism; Terpenes; Volatile Organic Compounds

The cotton aphid, Aphis gossypii (Homoptera: Aphididae), is increasing in importance as a pest worldwide since the introduction of Bt-cotton, which controls lepidopteran but not homopteran pests. The chemical ecology of interactions between cotton, Gossypium hirsutum (Malvaceae), A. gossypii, and the predatory lacewing Chrysoperla lucasina (Neuroptera: Chrysopidae), was investigated with a view to providing new pest management strategies. Behavioral tests using a four-arm (Pettersson) olfactometer showed that alate A. gossypii spent significantly more time in the presence of odor from uninfested cotton seedlings compared to clean air, but significantly less time in the presence of odor from A. gossypii infested plants. A. gossypii also spent significantly more time in the presence of headspace samples of volatile organic compounds (VOCs) obtained from uninfested cotton seedlings, but significantly less time with those from A. gossypii infested plants. VOCs from uninfested and A. gossypii infested cotton seedlings were analyzed by gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS), leading to the identification of (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), which were produced in larger amounts from A. gossypii infested plants compared to uninfested plants. In behavioral tests, A. gossypii spent significantly more time in the control (solvent) arms when presented with a synthetic blend of these four compounds, with and without the presence of VOCs from uninfested cotton. Coupled GC-electroantennogram (EAG) recordings with the lacewing C. lucasina showed significant antennal responses to VOCs from A. gossypii infested cotton, suggesting they have a role in indirect defense and indicating a likely behavioral role for these compounds for the predator as well as the aphid.

Topics: Acetates; Alkenes; Animals; Aphids; Behavior, Animal; Gas Chromatography-Mass Spectrometry; Gossypium; Pheromones; Terpenes; Volatile Organic Compounds

Natural enemies of herbivorous insects utilize numerous chemical cues to locate and identify their prey. Among these, volatile plant compounds produced after attack by herbivores may play a significant role (hereafter herbivore-induced plant volatiles or HIPVs). One unresolved question is whether the composition of the volatile cue blends induced by different herbivore species differ consistently enough to indicate not only that the plants are damaged by herbivores but also the identity of the herbivore species causing the damage. We studied HIPV production in the undomesticated plant species Datura wrightii in the laboratory when damaged by either of two leaf-chewing herbivore species, Lema daturaphila or Manduca sexta, or when damaged by L. daturaphila and the piercing-sucking bug, Tupiocoris notatus, or both L. daturaphila and T. notatus, for 24 hr. HIPV production was monitored 1 d before induction, the day of induction, and for 7 d after induction. In all experiments, both the quantities and composition of the HIPV blends varied with the time since induction as different components reached peak production at different times after induction. HIPV blends did not differ consistently with the herbivore species causing the damage. For plants damaged by both L. daturaphila and T. notatus, greater amounts of HIPVs were produced than by plants damaged by either species alone, but the amounts did not differ from that predicted as the sum from damage inflicted by each herbivore species independently. The HIPVs of D. wrightii are a general rather than specific indicator of damage by herbivores. Because generalist predators are the most abundant natural enemies in this system, general cues of herbivore damage may be all that are required to facilitate the discovery by predators of plants damaged by any of several suitable prey species.

Topics: Acetates; Alkenes; Animals; Datura; Insecta; Plant Leaves; Polycyclic Sesquiterpenes; Sesquiterpenes; Species Specificity; Terpenes; Time Factors; Volatile Organic Compounds