Many plants have natural defenses that repel pests. Plant
chemistry is a very important source of information for
insects which determine its oviposition behavior and its
choice of a host plant. Acceptance or rejection of a plant
is determined by the overall effect of the opposing positive
and negative semiochemical cues that the insect receives
from the environment (Dethier 1982). The identification
of plants (crops or weeds) that provide semiochemicals
beneficial to crops, such as repellents for the insect pests
and/or attractants to parasitoids and other natural enemies,
is important for pest management in the field.
Non-host chemicals may be used for insect pest
management in crops by interfering with orientation to the
host plant. The influence of non-host plant volatiles on the
olfactory, feeding and oviposition behavior of major insect
pests and various natural enemies have been extensively
studied (Schoonhoven 1968; Perrin and Philips 1978;
Dethier 1982; Bell and Carde 1984; Harborne1988;
Theunissen 1994). For example, onion thrips (Thrips
tabaci Lindeman) were significantly deterred by the
essential oils of marjoram (Origanum majorana L.),
lavender (Lavandula angustifolia L.) and mint (Mentha
arvensis L.), and by the oil of rosemary (Rosmarinus
officinalis L.). Furthermore, thrips feeding damage was
reduced as a result of linalool and eugenol application.
Evaluation of the potential of biologically active plant
volatiles against T. tabaci may provide a new approach to
the development of integrated pest management strategies
(Koschiera et al. 2002).