Exploring the Kairomone-Based Foraging Behaviour of Natural Enemies to Enhance Biological Control: A Review.

Kairomones are chemical signals that mediate interspecificinteractions beneficial toorganisms that detect the cues. These attractants can be individual compounds ormixtures of herbivore-induced plant volatiles (HIPVs) or herbivore chemicals such aspheromones, i.e., chemicals mediating intraspecific communication between herbivores.Natural enemies eavesdrop on kairomones during their foraging behaviour, i.e., locationof oviposition sites and feeding resources in nature. Kairomone mixtures are likelyto elicit stronger olfactory responses in natural enemies than single kairomones.Kairomone-based lures are used to enhance biological control strategies via theattraction and retention of natural enemies to reduce insect pest populations andcrop damage in an environmentally friendly way. In this review, we focus on ways toimprove the efficiency of kairomone use in crop fields. First,we highlight kairomonesources in tri-trophic systems and discuss how these attractants are used by naturalenemies searching for hosts or prey. Then we summarise examples of field applicationof kairomones (pheromones vs. HIPVs) in recruiting naturalenemies. We highlight theneed for future field studies to focus on the application of kairomone blends ratherthan single kairomones which currently dominate the literature on field attractants fornatural enemies. We further discuss ways for improving kairomone use through attractand reward technique, olfactory associative learning, andoptimisation of kairomone lureformulations. Finally, we discuss why the effectiveness ofkairomone use for enhancingbiological control strategies should move from demonstration of increase in the numberof attracted natural enemies, to reducing pest populationsand crop damage beloweconomic threshold levels and increasing crop yield