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Review
, 274 (1607), 151-64

Ecological Consequences of Interactions Between Ants and Honeydew-Producing Insects

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Review

Ecological Consequences of Interactions Between Ants and Honeydew-Producing Insects

John D Styrsky et al. Proc Biol Sci.

Abstract

Interactions between ants and honeydew-producing hemipteran insects are abundant and widespread in arthropod food webs, yet their ecological consequences are very poorly known. Ant-hemipteran interactions have potentially broad ecological effects, because the presence of honeydew-producing hemipterans dramatically alters the abundance and predatory behaviour of ants on plants. We review several studies that investigate the consequences of ant-hemipteran interactions as 'keystone interactions' on arthropod communities and their host plants. Ant-hemipteran interactions have mostly negative effects on the local abundance and species richness of several guilds of herbivores and predators. In contrast, out of the 30 studies that document the effects of ant-hemipteran interactions on plants, the majority (73%) shows that plants actually benefit indirectly from these interactions. In these studies, increased predation or harassment of other, more damaging, herbivores by hemipteran-tending ants resulted in decreased plant damage and/or increased plant growth and reproduction. The ecological consequences of mutualistic interactions between honeydew-producing hemipterans and invasive ants relative to native ants have rarely been studied, but they may be of particular importance owing to the greater abundance, aggressiveness and extreme omnivory of invasive ants. We argue that ant-hemipteran interactions are largely overlooked and underappreciated interspecific interactions that have strong and pervasive effects on the communities in which they are embedded.

Figures

Figure 1
Figure 1
Potential consequences of the interactions between honeydew-producing hemipterans and ants on plants. Arrows indicate the direction of effects, positive (+) and negative (−), and arrow width indicates the relative magnitude of effects. Solid arrows indicate direct effects, whereas dashed arrows indicate indirect effects. Ant–hemipteran interactions may provide a net benefit to plants (a) if the indirect positive effect of increased ant suppression of other (non-honeydew-producing) herbivores outweighs the direct negative effect of hemipterans on plants. In contrast, ant–hemipteran interactions may harm plants (b) if the direct negative effect of hemipterans on plants outweighs the indirect positive effect of increased ant suppression of other herbivores. Note that honeydew-producing hemipterans and other (non-honeydew-producing) herbivores may also interact indirectly via effects on host plant quality (effects not shown).
Figure 2
Figure 2
Percentage of studies that documented positive effects versus negative effects of ant–hemipteran interactions on plant fitness relative to (a) study system (natural or managed), (b) latitude (temperate or tropical), (c) host plant growth form (herbaceous or woody), (d) ant subfamily (Formicinae or Myrmicinae), (e) hemipteran suborder (Auchenorrhyncha or Sternorrhyncha) and (f) Sternorrhynchan superfamily (Aphidoidea or Coccoidea). Numbers above columns indicate the total number of studies in each category. See text for further details.
Figure 3
Figure 3
Conditionality in the consequences of a mutualistic interaction between ants and honeydew-producing hemipterans on a host plant based on the intensity of herbivory by other herbivores (including hemipteran insects that do not feed from plant phloem or produce honeydew). The cost of the interaction to the plant (in terms of loss of caused by honeydew-producing hemipteran damage to plants) is shown as the dotted curve and increases with an increasing density of honeydew-producing hemipterans. The benefit of the ant–hemipteran interaction to the plant (in terms of increased plant fitness caused by ant suppression of plant damage by other herbivores) is shown as the two solid curves. At a high level of herbivory by non-tended herbivores, the benefit of the ant–hemipteran interaction to the plant is predicted to outweigh the cost at all but extremely high levels of honeydew-producing hemipteran density. However, at a low level of herbivory by non-tended herbivores, the mutualism either provides only a slight fitness benefit (at lower hemipteran densities) or results in a net loss of fitness (at higher hemipteran densities).

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