Does the Aphid Alarm Pheromone (E)-β-farnesene Act as a Kairomone under Field Conditions?

Insect natural enemies use several environmental cues for host/prey finding, and adjust their foraging behavior according to these signals. In insects, such cues are mainly chemical, derived from the host plant or the prey itself. The aphid alarm pheromone, (E)-β-farnesene (EBF), is believed to be such a cue, because several aphid enemies are able to perceive EBF and show attractant behavior. These studies are, however, based mainly on electroantennogram or olfactometer assays, and often use unnaturally high pheromone concentrations. It is, therefore, unclear if EBF is used to locate prey in the field when only naturally released amounts are present. We monitored the frequencies and durations of plant visits by aphid natural enemies in the field using long-duration camera observations. By placing pheromone releasers emitting no, natural or exaggerated amounts of EBF next to small colonies of pea aphids (Acyrthosiphon pisum), we analyzed if EBF presence altered long-range foraging behavior of natural enemies. Thirteen potential groups of aphid natural enemies were observed in 720 hr of analyzed video data. There was no effect of EBF on the number of predator visits to an aphid colony, or on predator patch residence times. The number of plant visits increased at exaggerated EBF amounts but not at natural EBF levels. We conclude that while there may be potential for use of high EBF concentrations for agricultural pest management strategies, an ecological role of EBF as a kairomone in a natural context is doubtful.