Floral volatiles controlling ant behaviour

Abstract

Summary1. Ants show complex interactions with plants, both facultative and mutualistic, ranging from grazers through seed predators and dispersers to herders of some herbivores and guards against others. But ants are rarely pollinators, and their visits to flowers may be detrimental to plant fitness. 2. Plants therefore have various strategies to control ant distributions, and restrict them to foliage rather than flowers. These 'filters' may involve physical barriers on or around flowers, or 'decoys and bribes' sited on the foliage (usually extrafloral nectaries -EFNs). Alternatively, volatile organic compounds (VOCs) are used as signals to control ant behaviour, attracting ants to leaves and ⁄ or deterring them from functional flowers. Some of the past evidence that flowers repel ants by VOCs has been equivocal and we describe the shortcomings of some experimental approaches, which involve behavioural tests in artificial conditions. 3. We review our previous study of myrmecophytic acacias, which used in situ experiments to show that volatiles derived from pollen can specifically and transiently deter ants during dehiscence, the effects being stronger in ant-guarded species and more effective on resident ants, both in African and Neotropical species. In these plants, repellence involves at least some volatiles that are known components of ant alarm pheromones, but are not repellent to beneficial bee visitors. 4. We also present new evidence of ant repellence by VOCs in temperate flowers, which is usually pollen-based and active on common European ants. We use these data to indicate that across a wide range of plants there is an apparent trade-off in ant-controlling filter strategies between the use of defensive floral volatiles and the alternatives of decoying EFNs or physical barriers.

A dual function for 4-methoxybenzaldehyde in Petasites fragrans? Pollinator-attractant and ant-repellent

“…The floral volatiles of male Petasites fragrans plants have previously been shown to elicit repellence-related behaviour in Formica aquilonia ants (Willmer et al 2009). Here, we detected one prominent volatile, 4-methoxybenzaldehyde (hereafter 4-MoB), in the floral bouquet of P. fragrans.…”

“…P. fragrans was previously found to elicit particularly strong repellence-related behaviours in Formica aquilonia ants (Willmer et al 2009) (although there misnamed as P. hybridus). The single identified volatile was subsequently tested for ant-repellence using a two-way olfactometer.…”

“…Ant-repellent floral volatiles are a well-documented phenomenon, with examples from many different ecosystems (Junker and Blüthgen 2008;Willmer et al 2009;Junker et al 2011a). Their presence has typically been linked to the detrimental effects of ants on flowers.…”

“…Their presence has typically been linked to the detrimental effects of ants on flowers. Ants are generally poor pollinators, but frequently visit flowers for nectar where, in addition to nectar theft, they can deter legitimate pollinators with their aggressive behaviour, damage pollen with antimicrobial chemicals present on their integument, and cause physical damage to floral parts (see Willmer et al 2009 for a review).…”

Nectar palatability can selectively filter bird and insect visitors to coral tree flowers

“…Mutualisms between plants and animals are often exploited by cheats which receive benefits without conferring benefits to the other organism (Bronstein 2001 Examples include morphological structures that prevent non-mutualistic ants from gaining access to domatia of some legumes (Brouat et al 2001) and emission by Acacia flowers of volatiles that deter ants, but not bee pollinators (Willmer et al 2009). In plant pollination systems, secondary compounds in nectar may function as taste filters which deter animals which are morphologically or behaviourally poorly suited to be effective pollinators (Adler 2000).…”