Is there any evidence that aphid alarm pheromones work as prey and host finding kairomones for natural enemies?

Abstract

Abstract. 1. The aphid alarm pheromone (E)--farnesene (EBF) is often considered to be used by natural enemies as a prey/host finding kairomone. However, studies show opposing results, some appear to confirm an attraction of aphid natural enemies by EBF whereas others do not provide any evidence for the kairomone function of EBF.2. To clarify if aphid natural enemies are attracted by the amounts of EBF naturally emitted by aphids, the existing literature was reviewed about EBF attractiveness to aphid natural enemies with consideration of the amounts of EBF used in the studies.3. Thirty-one publications that investigated the ability of EBF, aphid cornicle secretion, and attacked aphids, to attract aphid natural enemies were found. Several studies showed an attraction by EBF, but these used much higher amounts of EBF than usually emitted by aphids during a predator attack. Studies investigating EBF amounts similar to what is emitted by aphids are rare and failed to show attraction. Only two studies document an attraction of natural enemies by attacked aphids.4. As EBF is emitted in very low amounts, not very stable, and only present after an attack, we suggest that aphid-derived EBF is not a suitable kairomone for most natural enemy species, especially when they are able to use alternative cues. As EBF, amongst other volatiles, is also emitted by herbivore-induced plants, we propose that natural enemies might use plant-derived EBF as a synomone to identify aphid-infested plants via an altered plant volatile bouquet.

Dealing with food shortage: larval dispersal behaviour and survival on non‐prey food of the hoverfly Episyrphus balteatus

“…During the local search on an aphid-infested plant, they may mark the areas they have already searched to avoid examining them again, as it is the case for ladybird larvae (Meisner & Ives, 2013). In close vicinity to an aphid colony under attack, they may be attracted by the aphid alarm pheromone (E)--farnesene (Vosteen et al, 2016c).…”

Defense of pyrethrum flowers: repelling herbivores and recruiting carnivores by producing aphid alarm pheromone

“…For an aphid alarm pheromone produced by plants to be effective it needs to mimic the purity and dynamics of the natural aphid pheromone and direct predators to the potential location New Phytologist of prey (Joachim et al, 2013;Vosteen et al, 2016). Here, we took a comprehensive field-observation-based tritrophic approach including a plant, aphid and predator.…”

“…These EbF-emitting plants elicited potent effects on the behavior of the aphid Myzus persicae (alarm and repellent responses) and its parasitoid Diaeretiella rapae (an arrestant response), suggesting effective direct and indirect defense by the constitutively released compound (Beale et al, 2006). However, since the early laboratory studies on aphid repellence (Gibson & Pickett, 1983) and predator attraction by prey-or plant-derived EbF (Abassi et al, 2000;Francis et al, 2005a,b;Harmel et al, 2007), no field or ecological evidence of effective, alarm-pheromone-based plant defense has been presented (Av e et al, 1987;Kunert et al, 2010;Bruce et al, 2015;Vosteen et al, 2016). Multiple explanations for this have been proposed.…”

Hoverfly preference for high honeydew amounts creates enemy‐free space for aphids colonizing novel host plants

“…This indicates that hoverflies mainly use short‐range aphid‐derived cues to select aphid‐infested plants for oviposition. Aphid presence is most likely detected by visual cues coming from the aphids themselves (Kan & Sasakawa ), since volatiles emitted by aphids, like the aphid alarm pheromone ( E )‐β‐farnesene, are emitted in too small amounts to be suitable cues for adult hoverflies and other mobile adult predators, and hoverflies were not attracted by pheromone releasers containing ( E )‐β‐farnesene under field conditions (Joachim & Weisser ; Vosteen, Weisser & Kunert ).…”