Summary1. With an expanding human population placing increasing pressure on the environment, agriculture needs sustainable production that can match conventional methods. Integrated pest management (IPM) is more sustainable, but not necessarily as efficient as conventional non-sustainable measures. 2. Being predatory and organized as superorganisms, ants possess traits making them suitable agents in IPM. Recent works on weaver ants Oecophylla spp. showcase ants as highly efficient pest controllers. A synthesis shows that weaver ants can reduce pest numbers and their damage and increase yields in multiple crops. Their efficiency is comparable to chemical pesticides or higher, while at lower costs. They provide a rare example of documented efficient conservation biological control. 3. Weaver ants share beneficial traits with almost 13 000 other ant species and are unlikely to be unique in their properties as control agents. A synthesis of applied work on other ant species illustrates potentials for control of arthropod pests, weeds and plant diseases in orchards, forestry and arable crops. 4. Synthesis and applications. By showing that ant biocontrol can match synthetic pesticides in a wide setting of agricultural systems, this review emphasizes the potential of managing ants to achieve sustainable pest management solutions. The synthesis suggests future directions and may catalyse a research agenda on the utilization of ants, not only against arthropod pests, but also against weeds and plant diseases. Lastly, it may stimulate implementation of already proven ant-based integrated pest management techniques.
It is well documented that ants can protect plants against insect herbivores, but the underlying mechanisms remain almost undocumented. We propose and test the pheromone avoidance hypothesis-an indirect mechanism where insect herbivores are repelled not only by ants but also by ant pheromones. Herbivores subjected to ant predation will experience a selective advantage if they evolve mechanisms enabling them to avoid feeding within ant territories. Such a mechanism could be based on the ability to detect and evade ant pheromones. Field observations and data from the literature showed that the ant Oecophylla smaragdina distributes persistent pheromones throughout its territory. In addition, a laboratory test showed that the beetle Rhyparida wallacei, which this ant preys on, was reluctant to feed on leaves sampled within ant territories compared with leaves sampled outside territories. Thus, this study provides an example of an ant-herbivore system conforming to the pheromone avoidance hypothesis.
Ants of the genus Oecophylkz are predators of other insects and are able to protect a variety of terrestrial plants against pest insects; however, observations on the ecology of these ants in mangrove forests are lacking. General observations on the ecology of Oecophylkz smaragdina were carried out in a Thai mangrove forest to determine if these ants can protect their host plants in less favorable mangrove habitats. Leaf herbivory and the density of 0. smaragdina ants were measured on Rhizophora mucronata trees at two sites. The results showed a negative correlation between ant density and herbivory. At both sites, the mean percent damaged leaf area was more than four times higher on trees without ants compared to "ant-trees." A significant negative correlation was found between tree mean percent leaf damage and the density of ants on the tree. Furthermore, on trees with ants, there was less herbivory on leaves close to ant nests compared to other leaves on the tree. Most damage was caused by chrysomelid beetles (62%) and sesarmid crabs (25%) and both types of herbivory were significantly reduced on ant-trees.
Ants possess properties that can be used to optimize plant production in agricultural systems. Ant services can be herbivore and pathogen protection and fertilization of their plant partners. They may, however, also harm plants by facilitating ant-attended herbivorous homopterans. To assess whether wood ants can be used in IPM-systems to improve apple production, we transplanted wood ants into a Danish apple plantation and tested whether ants (i) reduced the number of herbivores, (ii) led to higher amounts of leaf nutrients, (iii) controlled apple pathogens, (iv) increased homopteran abundance and (iv) whether these effects affected apple yields. During a two year study, we found that the wood ants significantly reduced the numbers of winter moth larvae, increased magnesium content in apple leaves (but did not affect 10 other nutrients), reduced the number of apples infected with apple brown rot and apple scab (on one apple variety) and increased aphid infections. In the first year, this led to higher apple production on ant trees, whereas ants had no effect on yields in the second year. It was evident that ants provided both services and disservices. If mutualistic ant-homopteran interactions can be disrupted, this would favor plant growth and open for the use of wood ants in sustainable plant management. We discuss how this may be accomplished. Alternatively, ants may be used short term to knock down pest outbreaks (before building up homopteran populations) or used in crops that do not host ant-attended homopterans.
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.
* In Benin cashew plantations, yields and nut quality are lost mainly as a result of insect pests. In the present study, we investigated the effectiveness of the African weaver ant Oecophylla longinoda as a biocontrol agent against Beninese cashew pests. * In a 2-year study, nut yield and quality were compared among: (i) trees with weaver ants O. longinoda; (ii) trees where weaver ants were sugar-fed; (iii) integrated pest management (IPM) trees with weaver ants combined with fruit fly bait spray; and (iv) control trees receiving no control measures. * All treatments with ants showed significantly higher yields than the control, with the IPM treatment leading to the highest yield. Compared with the control trees, the ants, ant sugar-fed and the IPM trees produced 78%, 122% and 151% more nuts, respectively. Nuts produced on control trees were of a higher quality on average because they were less damaged by thrips (probably because the fruit fly bait worked as a contact poison on thrips); this was also the case for the IPM treatment. In absolute numbers, however, trees in ant treatments produced more first-quality nuts. * To achieve a broader and effective control of both coreid bugs and thrips, a combination of weaver ants and supplementary compatible control measures is recommended. (Résumé d'auteur
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