References

422 V.Ninkovic,R.Glinwood,J.Pettersson
Fig.28.1. Allelobiosis: the process of chemical interaction between undamaged pants and
its effects on other trophic levels, e.g. insect herbivores and their natural enemies
plant coexistence and competition. However, from an ecological perspective,
its role is still only partly understood and its general evolutionary
importance is still a matter of speculation. For example, interactions of this
type may affect not only the plant, but also herbivores and their natural
enemies that are associated with the plant.
We have introduced a new term, allelobiosis,todescribethewidertrophic
effects of plant interaction via chemicals (Pettersson et al. 2003) (Fig. 28.1).
The three key aspects of our definition of allelobiosis are (1) the chemical
interaction occurs between undamaged plants, (2) the interaction may be
beneficial for the receiving plant and (3) the responses of the receiving plant
affect organisms at other trophic levels. Aspect 1 separates allelobiosis from
a large body of research on interplant signalling, which focuses on signals
released by infected/infested plants, while aspect 3 separates allelobiosis
from the plant-focussed approach of allelopathy.
In theory, chemicals released by one plant may have an informative value
for a neighbouring plant, and represent a stimulus that promotes changes
in the growth strategy of the ‘listening plant’. Potential effects on growth
are changes in biomass allocation that, in the longer term, increase a plant’s
capacity to exploit resources such as light, water and soil nutrients. The
altered growth strategy may also affect the physiological status of the plant,
with implications for other organisms such as herbivores and their natural
enemies.
In this review we explore the current knowledge of allelobiosis, and its
effects across three trophic levels. Although allelobiosis can take place via
several routes, including root exudates, we will focus here on plant volatiles.
Special reference will be made to experiments on a model system consisting
of barley, an aphid herbivore and a natural enemy, a ladybird.