Herbivore- and MeJA-induced volatile emissions from the redroot pigweed Amaranthus retroflexus Linnaeus: their roles in attracting Microplitis mediator (Haliday) parasitoids

摘要

The redroot pigweed Amaranthus retroflexus Linnaeus (Caryophyllales: Amaranthaceae), an annual weed, is a host plant of the cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae). Microplitis mediator (Haliday) (Hymenoptera: Braconidae) is a parasitoid of H. armigera. Here, the electrophysiological and behavioral responses of M. mediator to induced redroot pigweed volatiles were investigated. Female parasitoids were significantly attracted to odors from plants induced by H. armigera damage, H. armigera continuous feeding, and 10 mM methyl jasmonate (MeJA) spray. The gas chromatography-mass spectrometry (GC-MS) results demonstrated that there were significant changes in volatiles from these three treatments in comparison with the control. When the constitutive compound 6-methyl-5-hepten-2-one was emitted in significant amounts from treated plants, it could elicit a medium electrophysiological response (0.2 aecurrency value 0.8) , a significant behavioral response of M. mediator females. beta-Elemene, emitted from two treatments (plants damaged by H. armigera, plants with H. armigera continuous feeding), showed a very weak electrophysiological response (value 0.2), but was significantly attractive to M. mediator. The results showed that 6-methyl-5-hepten-2-one and beta-elemene might play important roles in mediating the foraging behavior of M. mediator. Further work will be conducted to evaluate the function of these two compounds under semi-field and field conditions and exploit them as attractants for M. mediator to control H. armigera.