Ants suppressing plant pathogens: a review

Abstract

Ant–plant mutualisms are usually regarded as driven by ants defending plants against herbivores in return for plant‐produced food rewards and housing. However, ants may provide additional services. In a review of published studies on ant–pathogen–plant interactions, we investigated whether ants’ extensive hygiene measures, including the use of ant‐produced antibiotics, extend to their host plants and reduce plant pathogen loads. From 30 reported species combinations, we found that the presence of ants lead to reduced pathogen levels in 18 combinations and to increased levels in 6. On average, ants significantly reduced pathogen incidence with 59%. This effect size did not differ significantly from effect sizes reported from meta‐analyses on herbivore protection. Thus, pathogen and herbivore protection could be of equal importance in ant–plant mutualisms. Considering the abundance of these interactions, ecological impacts are potentially high. Furthermore, awareness of this service may stimulate the development of new measures to control plant diseases in agriculture. It should be noted, though, that studies were biased toward tropical ant–plant symbioses and that the literature in the field is limited at present. Future research on plant pathogens is needed to enhance our understanding of ant–plant mutualisms and their evolution.

The effect of edaphic factors on the distribution and abundance of ants (Hymenoptera: Formicidae) in Iran

“…The second hypothesis is that ants provide services on the molecular scale instead of receiving rewards from plants, such as plant‐produced food and housing. Studies conducted by Offenberg and Damgaard (2019) show that ant-produced antibiotics spread to their host plants and reduce plant pathogenic loads, providing evidence of a special relationship between ants and plants, which firmly confirms our hypothesis. However, other ants' services to plants, such as pollination and soil movement, can also be considered.…”

New Tools for Conservation Biological Control: Testing Ant-Attracting Artificial Nectaries to Employ Ants as Plant Defenders

“…In both cases, trees with a high ant activity were significantly less affected, which may indicate the role of ants in limiting the spread of this epiphytic fungus. Indeed, effects on plants by ant antimicrobial secretions have already been documented in several cases, but the ecological weight of these interactions-not to mention their possible applications in agriculture-is far from being understood and in need of investigation [17,48,79]. The ability of ants to reduce the damage by apple scab (Venturia inequalis (Cooke) G. Winter (1875)) was recently documented [48].…”

“…Although ants may indirectly damage plants through this relationship, its cost-benefit ratio may still be beneficial overall for the plant if ant presence displaces more damaging herbivores [12]. Some plants produce nectars, other food rewards or offer shelter to ants in exchange for protection against herbivory, competing plants or even pathogens [13][14][15][16][17]. These rewards may also be aimed at distracting ants from tending sap feeders [18][19][20][21].…”

The Influence of Tree Diversity on Natural Enemies—a Review of the “Enemies” Hypothesis in Forests

“…Studying behavioral interactions under different tree diversity will be important to understand non-consumptive effects. Furthermore, predators can also influence non-herbivorous damage-causing organisms, for example, when ant activity suppresses plant pathogens [148]. Whether or not this is diversity-dependent is at present unknown, but could be an ecologically relevant extension of the "enemies" hypothesis.…”