Ants are undisputed masters at transforming the local environments they inhabit, with subsequent vast effects on soil chemical and hydrological processes. Yet, it remains unclear how deep into the subsoil these effects range, as most ant-soil studies focus on the topsoil. Furthermore, studies quantifying these effects on podzolized, and nutrient-poor heathland soils remain scarce. We excavated 15 Formica exsecta ant mounds on a long-term, unmanaged heathland in Denmark. We sampled soil moisture, soil penetration resistance (SPR), pH, total phosphorous content, and the thickness of each soil horizon at three positions at each mound: directly below the mound, at the edge of the mound, and an adjacent undisturbed reference soil. Results revealed that ant activity reduced soil moisture, loosened the soil, and increased the flow of total phosphorus to the deeper layers. Importantly, the cemented spodic horizons (hardpans) with waterlogging properties were penetrated by ant digging, resulting in potentially higher water infiltration into the subsoil. The ant activity within the otherwise undisturbed sandy subsoil below the hard pan caused a slight alteration in the thickness of each soil horizon and chemistry. These patchy, small-scale disturbances (mounds covered 0.06 % of the site) increase heathland soil heterogeneity and affect subsoil properties in time. We conclude that ant mounds may play a previously overlooked role in heathland soil dynamics by penetrating the heathland hardpans and manipulating soil chemistry and soil moisture. We argue that a viable mound-forming ant community is valuable for the soil heterogeneity of dry heathland ecosystems.

Weaver ants (Oecophylla smaragdina and O. longinoda) are famous for their impressive nest constructions where they weave together living leaves on their host plants. Also, they are known to protect tropical tree crops against insect pests and are thus being utilized for biological control. To optimize their use, nest numbers have been used to track weaver ant abundances in plantation, assuming the number of nests reflects ant numbers. In this study we compared nest size, the density of ants and the proportion of workers in nests between three host plants (cashew, citrus and mango) and between two seasons (rainy and dry). Nest size, ant density and worker proportion all differed between host species, whereas only nest size and worker proportion showed seasonal differences and only on mango and citrus, respectively. On hosts with smaller nests (in increasing size order: cashew, citrus mango), ant densities in the nests were higher, and the proportion of workers in the nests seemed to increase during seasons where food production on host trees decreased, or on hosts where more trophobionts were cultured inside nests. These results have implications for the development of methods used to estimate ant numbers and they raise interesting questions about the function of weaver ant nests.

BACKGROUND:Wood ants are promising biocontrol agents in fruit plantations because they prey on pest insects and inhibit plant diseases. However, these ants also attend plant-feeding homopterans to harvest their honeydew secretions, thereby increasing their numbers. This problem can be solved by offering ants alternative sugar sources that are more attractive than honeydew. From natural interactions, it is known that some species manipulate mutualistic partners toward loyalty by adding alkaloids to the food they offer their mutualists. Inspired by this, the addition of alkaloids might be used to make ants loyal to artificial sugar feeders and thus used to reduce populations of ant-farmed homopterans in ant-mediated biological control. We aimed to explore whether wood ants (Formica polyctena) would develop a taste preference for morphine-containing sugar solutions in two-choice laboratory tests. RESULTS:After having fed on a morphine/sugar solution for 1 week, ants showed a significant preference for morphine solutions compared with equal concentration sugar solutions without morphine. Furthermore, ants lost this preference after 6-9 days on a morphine-free diet. CONCLUSION:The results show that wood ants react to morphine in their food, enabling chemical manipulation of their behavior, most likely through a taste preference. Thus, ants are susceptible to manipulation by mutualistic partners in natural interactions and furthermore may be manipulated artificially in biocontrol programs to avoid ant-mediated build-up of homopteran populations. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Plant diseases cost the global economy billions of US dollars every year. The problem has mainly been addressed by using chemical pesticides, but recently, the use of ants has shown promising effects against plant pathogens. However, the mechanisms accounting for these effects have not yet been determined. One possible explanation is antimicrobial microorganisms associated with ants. Through controlled laboratory experiments, we investigated the inhibitory effects of wood ants (Formica polyctena) and their associated microorganisms against economically important plant pathogenic fungi. All live ants, extracts from crushed ants, and extracts from washed ants significantly inhibited the apple brown rot (Monilinia fructigena) while yielding the growth of other microbes. Furthermore, all investigated wood ants transferred microorganisms to their surroundings within 10 s when walking across a surface. We isolated the most dominant microorganisms deposited by walking ants and from washed ant extracts (i.e., strains likely found on the surface of ants), resulting in four bacterial cultures and one yeast. Two of these isolates, strain I3 (most closely related to Pseudomonas sichuanensis and P. entomophila) and strain I1b (most closely related to Bacillus mycoides), showed inhibitory effects against apple brown rot and apple scab (Venturia inaequalis), while strain I3 also inhibited gray mold (Botrytis cinerea) and Fusarium head blight (Fusarium graminearum). These results suggest that wood ants have potential as biological control agents against commercially relevant plant pathogens, and that their inhibitory effect might be at least partially caused by antibiotic compounds produced by their associated microorganisms.

BACKGROUNDAnts can become efficient biocontrol agents in plantation crops as they prey on pest insects and may inhibit plant pathogens by excreting broad-spectrum antibiotics. However, ants also provide a disservice by augmenting attended honeydew producing homopterans. This disservice may be avoided by offering ants artificial sugar as an alternative to honeydew. Here we tested the effect of artificial sugar feeding on aphid abundance in an apple plot with wood ants (Formica polyctena, Forster), and tested the effect of ant presence on apple scab (Venturia inaequalis, Cooke) disease incidence. RESULTSOver a 2-year period, sugar feeding eliminated ant-attended aphid populations on the apple trees. Furthermore, scab symptoms on both leaves and apples were reduced considerably on ant trees compared to control trees without ants. The presence of ants on the trees reduced leaf scab infections by 34%, whereas spot numbers on fruits were reduced by between 53 and 81%, depending on apple variety. In addition, the spots were 56% smaller. CONCLUSIONThis shows that problems with wood ant-attended homopterans can be solved and that ants can control both insect pests and plant pathogens. We therefore propose wood ants as a new effective biocontrol agent suitable for implementation in apple orchards and possibly other plantation crops. (c) 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Mound-forming ants are important ecosystem engineers as they increase habitat heterogeneity, thus supporting multiple biotic interactions. How these ant-mediated changes in abiotic factors translate into temporal biotic heterogeneity, is a less studied subject. In a case study localized on a Danish heath, we investigated how ant mounds (mineral and organic mounds) affected the phenology and flowering success of five plant species growing on or between ant mounds (Lasius flavus and Formica exsecta). Specifically, we focused on the phenophases’ stem elongation, flowering and seed set. All plant species showed significantly earlier phenophases on the mounds compared to control patches between mounds. These advances resulted in two distinct flowering seasons for one plant species and prolonged continuous flowering seasons for the four other species, when mound and non-mound plant seasons were combined. Likewise, stem elongation and seed set seasons were prolonged, with either two distinct seasons or one continuous season, depending on plant species. Two plant species exhibited increased survival up to the flowering stage when growing on ant mounds, since they flowered before a drought killed a large part of the population. Probable drivers behind these effects, as revealed by a structural equation model, were elevated surface temperature and other soil edaphic factors responsible for plant growth. Furthermore, the direct effects of the ant mounds were nearly twice as high for the organic mounds of F. exsecta compared with the mineral mounds of L. flavus. Possible implications are more resilient ecosystems, as prolonged seasons can mitigate phenological mismatches between interacting species.

Wood ants are promising biocontrol agents in fruit plantations as they prey on pest insects and inhibit plant diseases. However, ants also attend plant-feeding homopterans to harvest their honeydew secretions thereby increasing their numbers. This problem can be solved by offering ants alternative sugar sources that are more attractive than honeydew. From natural interactions, it is known that some species manipulate mutualistic partners to loyalty, by adding alkaloids to the food they offer their partners. Inspired by this, the addition of alkaloids might be used to make ants loyal to artificial sugar feeders and thus used to reduce populations of ant-farmed homopterans in agriculture. We tested if wood ants (Formica polyctena) developed addiction to morphine containing sugar solutions in two choice laboratory tests. After having fed on a morphine/sugar solution for one week, ants showed a significant preference for morphine solutions compared to equally concentrated sugar solutions without morphine. Furthermore, then ants lost this preference after six to nine days on a morphine-free diet. This show that wood ants react to morphine and possibly other alkaloids and thus possess the physiological mechanisms enabling a chemical manipulation of their behavior. They are thus vulnerable to manipulations by mutualistic partners in natural interactions and furthermore may be manipulated artificially in biocontrol programs to avoid their building up of homopteran populations.

Plant diseases are a growing threat to plant production and food security. An accumulating number of studies show that ants and their bacterial symbionts produce antibiotics that are potentially effective against plant pathogens. From 14 publications covering 246 ant antibiotic-pathogen combinations, we evaluated the effectiveness of ant-derived chemicals (produced by ants or their microbiomes) in combatting plant pathogens. In a meta-analysis, we quantified the effect of ant chemicals on plant pathogens and compared it with the effect on other micro-organisms. Twenty-two ant secretions and 30 ant symbionts inhibited 20 and 10 plant pathogens, respectively, including major plant diseases and resistant strains. Ant-derived antibiotics showed broad-spectrum effects. Ant chemicals were antagonistic to plant pathogens in 93% of all tested combinations and microbiomes in 19%. All tested ant species contained antagonistic ant chemicals, and 10 of the 12 examined ant microbiomes contained at least one antagonistic symbiont. Ant chemicals had an overall negative effect on micro-organisms and were more detrimental to plant pathogens compared to other micro-organisms. Policy implications. By showing that ant-derived antibiotics inhibit a wide range of economically important plant pathogens, we emphasize the potential of ant chemicals and live ants to protect plants. We recommend attention to this topic and provide recommendations for future research and management directions that may facilitate a new path in the development of efficient and sustainable plant protection.

The current livestock sector is a large contributor to the environmental challenges facing the world. To reduce the environmental impact of food production, a change of the sector is necessary. Entomophagy could be a step towards a more sustainable protein production. However, the insect farming community has a short history compared to conventional livestock, thus, it lacks knowledge of how a profitable mass production of insects is established. In this study we aimed to find the optimal relative humidity (RH) for production of larvae of a popular species for insect farming; the yellow mealworm,Tenebrio molitor. More specifically we tested the effect of a RH of 43, 51, 68, 75 and 84% on the survival rate, mass and length ofT. molitor larvae, from hatching and two weeks forward. Control of RH was achieved using the saturated salt solution method, and the temperature was kept at 30 °C. Experiments were carried out over 12 weeks. The sample size was 100 larvae and eight replicates per treatment. Results showed that the RH had no effect on larval survival rate but had a significant effect on individual larvae mass and length after three weeks. Larval mass and length increased with humidity, and larvae reared at a RH of 84% were 1.96 times heavier and 1.31 times longer than larvae raised at 43%. Hence, for an industrial mass producer ofT. molitor larvae, applying close to the optimal RH of 84% would likely result in an increased larvae size at harvest and a faster growth rate, ultimately leading to a higher yield.

Thus far the articles in the series JOD calls the "Organization Zoo" have employed the notion of a "zoo" metaphorically to describe an array of human institutions. Here we take the term literally to consider the design of the most complex organizations in the living world beside those of humans, a favorite of insect zoos around the world: ant colonies. We consider individuality and group identity in the functioning of ant organizations; advantages of a flat organization without hierarchies or leaders; self-organization; direct and indirect communication; job specialization; labor coordination; and the role of errors in innovation. The likely value and limitations of comparing ant and human organizations are briefly examined.

Ecological intensification of cropping systems aims at restoring multi-functionality while supporting current productivity levels. Intercropping is a form of ecological intensification involving ecological processes beneficial to farmers that do not take place in monocultures. Thus, it represents a practical approach to decrease the use of synthetic inputs such as insecticides in cultivated systems. Whereas insecticide reduction via intercropping-facilitated suppression of aphids is reported in literature, the majority of published studies focussed on herbaceous crops. Thus, the effect of intercropping on aphid populations of cultivated trees remains largely unaddressed. In this study we hypothesized that intercropping a specific companion plant within perennial crops would divert ant attendance from an aphid attacking the crop to another aphid feeding on the newly introduced plant, reducing aphid damage on the crop. We tested our hypothesis in the system of apple (Malus domestica Borkhausen), the rosy apple aphid (Dysaphis plantaginea Passerini) and the black garden ant (Lasius niger L.). Bean plants (Vicia faba) with the black bean aphid (Aphis fabae Scopoli) were intercropped within apple trees inoculated with D. plantaginea. We measured ant attendance, aphid development and survival as well as honeydew composition on both plant species through semi-field and field experiments. The majority of ants chose to attend A. fabae over D. plantaginea in the semi-field experiment with potted plants. In the orchard, a larger majority of scouts were scored on A. fabae over D. plantaginea. A higher number of D. plantaginea colonies remained active in the apple control, whilst they were almost eradicated by intercropping. Although chemical analyses of honeydew disclosed differences in the carbohydrate and amino acid profiles between aphid species, the difference in honeydew composition did not explain the preference for A. fabae. Ants did not discriminate between the two honeydew mimics both in laboratory and field bioassays. Our results showed the potential of intercropping apple trees with beans as a method to reduce ant attendance and thus colony survival. We propose that intercropping represents a bottom-up approach towards ecological intensification of perennial crops. Together with other ecosystem-based measures such as habitat management, intercropping should be considered when planning ecosystem redesign to increase biological control of pests.

Maintaining heathland ecosystems in an early successional stage is a major aim of most management regimes, such as harvesting, burning or grazing. However, how these types of management affect important ecosystem engineers such as ants, are poorly understood. We registered the density of ant colonies in managed plots (harvested, burned and grazed) and plots with long succession (so forth unmanaged) across six different dry lowland heath sites. With these data, we investigated how composition and richness varied across management regimes and elucidated the direct effects of management from the indirect effects of environmental covariates. Ant species richness was significantly lower in managed plots compared to unmanaged plots. Harvest and grazing regimes were associated with the lowest richness, while intermediate richness was registered in burned plots. Smallest variation in species composition was found in the harvested, followed by grazed, burned and unmanaged heathlands. There was an overall negative association between abundances of organic mound forming species and all types of management, while non-mound forming species where negatively affected by grazing. In addition, Non- and organic mound forming species were indirectly affected through decreasing vegetation complexity. Only ants with mineral mounds benefitted from grazing and burning, but not from harvesting. To promote ant richness and abundance, we propose to downscale the frequency and intensity of management, as well as designating certain parts of the heathland area for later successional vegetation stages.

Red wood ants of the Formica rufa group are important ecosystem engineers throughout the Northern Hemisphere with potential to be commercially produced and used as predatory agents in biological control programs. However, in order to do that, their mutualistic relationship with aphids needs to be disrupted. This may be achieved by developing artificial sugar-based solutions with a composition that makes them more attractive than aphid honeydew. The present field study investigated Formica rufa’s preference for several sugar and amino acid sources, as well as potential seasonal changes in these preferences. Red wood ants consistently preferred sucrose to monosaccharides and were most attracted to solutions containing an amino acid source, albeit seasonal differences were observed with regard to which amino acid sources were most preferred. Recruitment to offered sugar solutions was highest during July, when colony requirements were high, and during October, when alternative food sources were scarce. Since ant preference for sugar solution constituents seems to be species-specific and show seasonal dynamics, artificial food aimed at disrupting ant-aphid mutualisms should be tailored to individual species and seasons.

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.

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.

Artificial sugar solutions can be used to disrupt the mutualism between aphids and ants. This provides natural enemies with increased access to aphid populations, thus enhancing biocontrol of hemipteran pests. However, research suggests that artificial solutions should be tailored to specific species in order to maximize the desired result. In this study, we test the effect of an alkaloid, caffeine, and a non-protein amino acid, gamma-aminobutyric acid (GABA), on preference for sucrose solutions in two ant species, Lasius niger and Oecophylla smaragdina. These secondary metabolites have been shown to have attractive capabilities in other species of insects, who favor nectars from plants containing these compounds. In our first experiment, both species significantly preferred solutions containing GABA over sucrose-only controls, albeit L. niger favored higher concentrations of the amino acid. Caffeine did not significantly increase preference for sugar solutions in either of the tested species, and ants significantly dispreferred the highest concentration of caffeine offered. When the two metabolites were tested simultaneously against sucrose only, L. niger fed equally from all solutions, while O. smaragdina dispreferred caffeine. Thus, while GABA seems to be a promising ant attractant, caffeine is not an adequate choice, at least at the concentrations tested in this experiment.

Ants can due to their high numbers and by being organized as superorganisms provide a number of services for plants including commercial crops. First, ants may prey on or deter arthropod and in some cases even vertebrate pests (Way & Khoo 1992; Goheen & Palmer 2010). Secondly, they may fertilize their host plants by depositing fecal spots on plant tissue. These fecal spots may contain important nutrients that can be taken up directly by plant leaves (Vidkjaer et al. 2016; Pinkalski et al. 2018). In addition, ants may enrich the soil around plant roots with increased nutrient levels due to their foraging activities (Folgarait 1998; Frouz et al. 2008; Wagner & Fleur Nicklen 2010). Lastly, ants may also provide plant services by reducing plant pathogen incidence. For example by eating fungal spores (Letourneau 1998), excrete antibiotics (Peng & Christian 2005; Gonzalez-Teuber, Kaltenpoth & Boland 2014) or by deterring diseases vectors (Letourneau 1998; Roux et al. 2011). Provision of these three services by ants may lead to highly effective biocontrol programs. In some cases ant based biocontrol is more efficient than conventional control based on synthetic pesticides, and even at lower costs (Offenberg 2015). Not all ant activities are positive for plants. Many ant species attend honeydew-producing homopterans that feed on plant sap and that can act as disease vectors (Delabie 2001). As ants improve hygiene and protect homopterans partners against natural enemies, they may increase in numbers when ant-attended. In this way ants may become indirectly harmful to plants (Wackers et al. 2017) even though cases exists where ant-attended homopterans show a positive net effect on plant fitness as the presence of homopterans lead to increased ant activity ultimately leading to protection against more detrimental herbivores (Styrsky & Eubanks 2007). The importance of this disservice to agriculture is illustrated by a number of research activities aimed at developing techniques to disrupt ant-homopteran symbioses in commercial crops. For example by preventing ants access to plant canopies by placing sticky barriers around tree trunks or by offering sugar to ants via artificial feeders (Nagy, Cross & Marko 2013; Nagy, Cross & Marko 2015; Wackers et al. 2017). The latter will provide ants with a carbohydrate source that is an alternative to the honeydew produced by the attended homopterans. This alternative may result in ants neglecting their partners or even lead to ants starting to prey on them (Offenberg 2001). In the present study we evaluated the services and disservices provided by wood ants (Formica polyctena) that was transplanted into an apple plantation to control winter moth larvae.

Ants can function efficiently as biocontrol agents in open field horticulture. Temperate wood ants can control forest pests, including species damaging forest regeneration plots and fruit plantations. Thus, they possess potential as biocontrol agents in open field horticulture, if they can persist in these systems. Here we present observationson activity and survival of wood ants transplanted from forests into different types of plantations. Mound fragments were transplanted into a conifer seedling plot, an organic and a conventional Christmas tree plantation, and into an organic apple plantation. Colonies survived at least one year in all types of plantations. In some cases, however, ants moved to new locations or migrated between mound fragments, leaving some inactive. Our compiled experiences suggest that this can be prevented by providing a minimum mound size, keeping a minimum spacing between mounds and incorporation of sand and scent marked wood pieces from donor colonies to imitate naturally occurring nests. We also observed that the ants preyed upon and significantly reduced the number of winter moth larvae (Operophtera brumata – a pest in apple and other fruit orchards) in two of four apple varieties. In conclusion, wood ants were tolerant to highly diferente habitat settings and will likely persist in most types of perennial horticultural systems, if managed properly. As they prey on winter moths and multiple other pest species, they are a potential new biocontrol agent for open agricultural systems.