Plants infested with a single herbivore species can attract natural enemies through the emission of herbivoreinduced plant volatiles (HIPVs). However, under natural conditions plants are often attacked by more than one herbivore species. We investigated the olfactory response of a generalist predators Macrolophus caliginosus to pepper infested with two-spotted spider mites, Tetranychus urticae, or green peach aphid, Myzus persicae, vs. plants infested with both herbivore species in a Y-tube olfactometer set up. In addition, the constituents of volatile blends from plants exposed to multiple or single herbivory were identified by gas chromatography-mass spectrometry (GC-MS). The mirid bugs showed a stronger response to volatiles emitted from plants simultaneously infested with spider mites and aphids than to those emitted from plants infested by just one herbivore, irrespective of the species. Combined with results from previous studies under similar conditions we infer that this was a reaction to herbivore induced plant volatiles. The GC-MS analysis showed that single herbivory induced the release of 22 additional compounds as compared with the volatiles emitted from clean plants. Quantitative analyses revealed that the amount of volatile blends emitted from pepper infested by both herbivores was significantly higher than that from pepper infested by a single herbivore. Moreover, two unique substances were tentatively identified (with a probability of 94% and 91%, respectively) in volatiles emitted by multiple herbivory damaged plants: a-zingiberene and dodecyl acetate.
Cultivars of shredded iceberg lettuce (Lactuca sativu L.) 'Saladin', 'Santis', 'Telda' and 'Roxette' responded in a parallel way to four modified atmosphere (MA) packaging treatments. Moderate vacuum packaging (mvp) in 80 pm polyethylene (PE) inhibited enzymatic browning over lo-day storage at 5°C. When lettuce was packaged in 80% O,, 20% CO, (80/20), more browning occured in SL3-bags (59 Frn multilayer coextruded film) than in PE-bags. Polyphenol oxidase activity declined during storage in all 4 atmospheres, with lowest activity in PE-80/20. Endogenous ascorbic acid (AA) did not act as an efficient antioxidant in delaying browning. Total carbohydrate content (TC) declined slightly during storage. Tristimulus color measurements correlated highly with visual ratings.
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