The aphid alarm pheromone (E)-β-farnesene does not act as a cue for predators searching on a plant

Insect enemies use several environmental cues for host or prey finding. In insects these cues are often chemical, deriving from the host plant or from the prey itself. The aphid alarm pheromone (E)-β-farnesene (EBF) that is emitted by aphids when attacked by a predator is believed to be such a cue, as it has been shown to be perceived by several aphid enemies. It is unclear, however, if EBF is used as an arrestant stimulus or a cue for short-range prey localization, i.e., attractant stimulus, on the plant. We observed the searching behavior of larvae of two aphid predators, lacewing (Chrysoperla carnea (Stephens), Neuroptera—Chrysopidae) and ladybird (Coccinella septempunctata L., Coleoptera—Coccinellidae), on a plant where an aphid was fixed, in the presence and absence of EBF, and under field and laboratory conditions. EBF had no effect on predator searching behavior, either when natural amounts of 50 ng EBF or unnaturally high amounts of 1,000 ng were used. EBF also did not induce longer predator patch residence times under laboratory (ladybird only: 600.8 ± 35.1 s) and field (ladybird: 644.9 ± 50.7 s, lacewing: 1,108.4 ± 49.5 s) conditions. Predators found the aphid on the plant within the allocated time in only 34.72 and 17.13 % of the cases in the laboratory and field, respectively, but the presence of EBF did not increase the foraging success. We conclude that aphid alarm pheromone is not used as an arrestant cue for these important aphid predators nor does it have a short-range attractant function.