Aphids, through their close association with plants, cause systemic release
of semiochemicals. These may have negative effects on subsequent aphid col
onisation and can also have positive roles with insects that are antagonist
ic to aphid development, for example parasitoids. One of the semiochemicals
involved in host selection by aphids is methyl salicylate. and since this
compound was shown to have a role as a plant stress signal, the hypothesis
that aphids might facilitate identification of new plant signals was examin
ed. Confirmation was obtained during an investigation of avoidance of unsui
table hosts by the lettuce aphid, Nasonovia ribis-nigri. (Z)-Jasmone was id
entified as a plant-derived semiochemical acting negatively for a number of
aphid species, and positively for insect antagonists such as parasitoids a
nd predators. However, when the compound was employed at 0.1 ppm in air abo
ve intact plants, these plants then attracted aphid parasitoids long after
the (Z)-jasmone itself was no longer detectable, A specific interaction was
proposed. since the (Z)-jasmone appeared to be selectively taken up by the
plants. Aerial interactions between intact barley plants from different cu
ltivars, which may be differentially releasing stress associated signals, c
an also influence acceptability to aphids. Furthermore, it has been shown t
hat exudates from the roots of aphid-infested plants, grown hydroponically
or in soil, cause intact plants to become more attractive to parasitoids. (
C) 2001 Published by Elsevier Science Ltd.