Abstract:
Kairomones are chemical signals that mediate interspecific interactions beneficial to
organisms that detect the cues. These attractants can be individual compounds or
mixtures of herbivore-induced plant volatiles (HIPVs) or herbivore chemicals such as
pheromones, i.e., chemicals mediating intraspecific communication between herbivores.
Natural enemies eavesdrop on kairomones during their foraging behaviour, i.e., location
of oviposition sites and feeding resources in nature. Kairomone mixtures are likely
to elicit stronger olfactory responses in natural enemies than single kairomones.
Kairomone-based lures are used to enhance biological control strategies via the
attraction and retention of natural enemies to reduce insect pest populations and
crop damage in an environmentally friendly way. In this review, we focus on ways to
improve the efficiency of kairomone use in crop fields. First, we highlight kairomone
sources in tri-trophic systems and discuss how these attractants are used by natural
enemies searching for hosts or prey. Then we summarise examples of field application
of kairomones (pheromones vs. HIPVs) in recruiting natural enemies. We highlight the
need for future field studies to focus on the application of kairomone blends rather
than single kairomones which currently dominate the literature on field attractants for
natural enemies. We further discuss ways for improving kairomone use through attract
and reward technique, olfactory associative learning, and optimisation of kairomone lure
formulations. Finally, we discuss why the effectiveness of kairomone use for enhancing
biological control strategies should move from demonstration of increase in the number
of attracted natural enemies, to reducing pest populations and crop damage below
economic threshold levels and increasing crop yield.
