Volatiles From Brassica Oleracea Infested By Plutella Xylostella (L.) And Their Effects

Induced host-plant resistance to insect herbivores is a common phenomenon in the plant kingdom.The quality and quantity of the blend of volatiles produced by plants can be changed by herbivores andother wounding. Herbivore-induced volatiles directly inhibit and repel herbivores or defend the plantindirectly by luring the enemies of the herbivore. At the same time, the volatiles from infested plantscan mediate the defensive responses of uninfested neighbors. The use of herbivore-induced volatiles inplant-plant communication has been reported in a few publications. In this study, the volatilecompounds produced by Brassica oleracea plants that were undamaged, mechanically damaged,volatile-induced, or infested with Plutella xylostella were collected by Tenax traps and identified by gaschromatography linked mass spectrometry (GC-MS). The effect of volatiles from infested plants onneighboring plants was also determined. Some of the compounds differentially released by the differenttreatments were selected for bioassays using electroantennogram (EAG) and Y-shaped olfactometers toexamine their effects on Plutella xylostella. The results are as follows.(1) Larvae were most efficiently attracted to undamaged leaves and extracts, followed byvolatile-induced, mechanically damaged and herbivore-damaged leaves and extracts.(2) The volatiles produced by B. oleracea included aldehydes, alcohols, terpenes, esters, alkanesand other compounds. After insect attack, the release of volatiles increased markedly. Volatile releaseincreased under the different treatments as follows: herbivore-damaged plants> volatile-inducedplants> mechanically damaged plants> undamaged plants. The volatiles produced by the differenttreatments of B. oleracea differed in composition. Benzyl alcohol, carvone, farnesene, nerolidol,caryophyllene, calamenene, and cadinene were only detected in herbivore-damaged plants, whilelinalool and2-hexyl-1-octanol were detected in demaged plants and volatile-induced plants. The resultsdemonstrated that the release of volatiles increased in herbivore-damaged plants and mechanicallydamaged plants and that the volatiles from the herbivore-damaged plants could induce neighboringplants to release more volatiles than undamaged plants.(3) The responses of Plutella xylostella to characteristic compounds at different concentrationswere measured by EAG. Aldehydes had the highest EAG-response value followed by alcohols, olefinand carvone. The response intensity generally increased with higher concentrations except for benzylalcohol and linalool. Male moths were observed to have stronger responses to volatiles than femalemoths by EAG. Male moths responded more intensely to E-2-Hexen-1-al and benzaldehyde, but femalemoths responded more intensely to nonanal and benzaldehyde than to other substances.(4) The Y-tube bioassay showed that the effect of the volatiles (attraction or repulsion) on Plutellaxylostella was significantly different regardless of whether the volatiles were at the same or differentconcentrations. Female moths were attracted by aldehyde, benzaldehyde, nonanal and carvone and wererepelled by benzyl alcohol at a volume rate of1:10. Male moths were attracted by aldehyde,benzaldehyde, nonanal, and caryophyllene and were repelled by octanol, benzyl alcohol, linalool andfarnesene at a volume rate of1:10. Female moths were repelled by farnesene and attracted by aldehydeand nonanal at a volume rate of1:100, while male moths were repelled by linalool and farnesene at high concentrations and attracted at low concentrations. In general, moths showed a strong response to mostvolatiles at high concentrations and almost no response at low concentrations. However, male mothswere attracted by carvone at low concentrations and repelled at high concentrations.In summary, the quality and quantity of volatiles produced by herbivore-damaged plants werespecies-specific and different from the volatiles produced by mechanically damaged plants. Thevolatiles from DBM-damaged plants could act as signals to stimulate neighboring plants into releasingmore volatiles. The volatile compounds from herbivore-damaged plants were shown to repel Plutellaxylostella by Y-tube and EAG bioassays. This study provides insights into the function of volatiles inthe interactions between plants, herbivores and natural enemies and lays the foundation for usinginduced plant defenses in pest management.