Herbivore‐induced emissions of maize volatiles repel the corn leaf aphid, Rhopalosiphum maidis

Abstract

When maize plants, Zea mays L., are mechanically damaged and the damaged sites are treated with caterpillar regurgitant, the plants will release a specific blend of volatiles. It is known that these volatiles can be attractive to natural enemies of herbivores. We hypothesise that the plant volatiles constitute part of the induced plant defence and that herbivores will be affected by the odours as well. In laboratory and semi-field studies this hypothesis was tested for the aphid Rhopalosiphum maidis (Fitch) (Rhynchota, Sternorrhyncha, Aphididae).In a Y-tube olfactometer significantly more aphids chose the odour of healthy, undamaged maize seedlings when tested against clean air or plants treated with regurgitant. Clean air was chosen more often when tested next to the odour of treated plants. This apparently repellent effect of the odour of treated plants was significant for winged aphids, but not for the wingless aphids.In field experiments aphids were released in the centre of circles of eight potted maize plants. Four plants in each circle were damaged and treated with caterpillar regurgitant while the other plants were left unharmed. At different intervals after aphid release, the number of aphids was counted on each plant. Significantly fewer winged and wingless aphids were found back on treated plants than on healthy plants.We suggest that herbivores may be repelled by the odours because they could indicate that: 1) the plant has initiated the production of toxic compounds; 2) potential competitors are present on the plant; 3) the plant is attractive to parasitoids and predators. Aphids may be particularly sensitive to induced maize volatiles because one of the major compounds emitted by the plant is (E)-β-farnesene, which is a common alarm pheromone for aphids. Collections and analyses of the odours emitted by crushed R. maidis confirmed that it too emits (E)-β-farnesene when stressed. The results are discussed in context of plant defence strategies and their possible exploitation for the control of pest insects.

Two Herbivore-Induced Cytochrome P450 Enzymes CYP79D6 and CYP79D7 Catalyze the Formation of Volatile Aldoximes Involved in Poplar Defense

“…For example, maize volatiles emitted from herbivore-damaged seedlings were shown to repel the corn leaf aphid (Rhopalosiphum maidis) (Bernasconi et al, 1998). However, in this study, we did not observe any repellence of early instar gypsy moth caterpillars by the major poplar volatile aldoximes (E/Z)-2-methylbutyraldoxime and (E/Z)-3-methylbutyraldoxime in the course of our olfactometer experiments ( Figure 7A).…”

Evaluating the Induced-Odour Emission of a Bt Maize and its Attractiveness to Parasitic Wasps

“…HP GC Chemstation software was used to quantify all major components based on the known quantity of internal standards. Initial identification of most compounds was based on comparisons of retention times with those from previous studies (Bernasconi et al, 1998;Turlings & Benrey, 1998) and was confirmed with the mass spectrometry analysis of some samples. For this purpose 3 ll aliquot were injected in pulsed splitless mode into a GC, using the same column and temperature programme (Agilent 5973, transfer line 230°C, source 230°C, quadrupole 150°C, ionisation potential 70 eV, scan range 30-240 amu).…”

Belowground Chemical Signaling in Maize: When Simplicity Rhymes with Efficiency

“…The role of volatiles in the attraction of such natural enemies was first brought to light in studies on the interactions between arthropods and plant leaves. Results revealed that herbivore attack induces emissions of volatile organic compounds (VOC) attractive to parasitoids and predators Sabelis 1988, Turlings et al 1995;De Moraes et al 1998), and this role of induced volatiles in tritrophic interactions has also been demonstrated under realistic field conditions (Bernasconi et al 1998;De Moraes et al 1998;Thaler 1999;Kessler and Baldwin 2001). While the aboveground portion of a plant is obviously essential for photosynthesis and reproduction, the root system is also of vital importance.…”