Predator and parasitoid attacking ant-attended aphids: effects of predator presence and attending ant species on emerging parasitoid numbers

Interaction between a predator and a parasitoid attacking ant-attended aphids was examined in a system on photinia plants, consisting of the aphid Aphis spiraecola, the two ants Lasius japonicus and Pristomyrmex pungens, the predatory ladybird beetle Scymnus posticalis, and the parasitoid wasp Lysiphlebus japonicus. The ladybird larvae are densely covered with waxy secretion and are never attacked by attending ants. The parasitoid females are often attacked by ants, but successfully oviposit by avoiding ants. The two ants differ in aggressiveness towards aphid enemies. Impacts of the predator larvae and attending ant species on the number of parasitoid adults emerging from mummies per aphid colony were assessed by manipulating the presence of the predator in introduced aphid colonies attended by either ant. The experiment showed a significant negative impact of the predator on emerging parasitoid numbers. This is due to consumption of healthy aphids by the predator and its predation on parasitized aphids containing the parasitoid larvae (intraguild predation). Additionally, attending ant species significantly affected emerging parasitoid numbers, with more parasitoids in P. pungens-attended colonies. This results from the lower extent of interference with parasitoid oviposition by the less aggressive P. pungens. Furthermore, the predator reduced emerging parasitoid numbers more when P. pungens attended aphids. This may be ascribed to larger numbers of the predator and the resulting higher levels of predation on unparasitized and parasitized aphids in P. pungens-attended colonies. In conclusion, a negative effect of the predator on the parasitoid occurs in ant-attended aphid colonies, and the intensity of the interaction is affected by ant species.     

Adaptations of Coccinella magnifica Redtenbacher, a Myrmecophilous Coccinellid, to Aggression by Wood Ants (Formica rufa Group). I. Adult Behavioral Adaptation, Its Ecological Context and Evolution

Coccinella magnifica is an obligate associate of Formica rufa-group ants. The congener Coccinella septempunctata can serve as a model for its nonmyrmecophilous ancestor. Formica rufa behavior toward these two ladybirds, and their behavior, was compared. Although C. magnifica was rarely attacked on ant trails, it was usually attacked on tended aphid colonies. Coccinella septempunctata was more readily attacked. The two ladybirds' behavior was similar on trails, but C. magnifica used more defense and C. septempunctata more rapid escape behavior on aphid colonies. Only C. magnifica fed upon tended aphids. Chemical adaptation to overcome ant aggression probably exists in C. magnifica, but it possesses almost no novel behaviors to counter ant aggression. Instead, modifications have occurred in the expression of behaviors present in C. septempunctata.     

Larvae of the green lacewing <Emphasis Type="Italic">Mallada desjardinsi</Emphasis> (Neuroptera: Chrysopidae) protect themselves against aphid-tending ants by carrying dead aphids on their backs

Larvae of the green lacewing Mallada desjardinsi Navas are known to place dead aphids on their backs. To clarify the protective role of the carried dead aphids against ants and the advantages of carrying them for lacewing larvae on ant-tended aphid colonies, we carried out some laboratory experiments. In experiments that exposed lacewing larvae to ants, approximately 40% of the larvae without dead aphids were killed by ants, whereas no larvae carrying dead aphids were killed. The presence of the dead aphids did not affect the attack frequency of the ants. When we introduced the lacewing larvae onto plants colonized by ant-tended aphids, larvae with dead aphids stayed for longer on the plants and preyed on more aphids than larvae without dead aphids. Furthermore, the lacewing larvae with dead aphids were attacked less by ants than larvae without dead aphids. It is suggested that the presence of the dead aphids provides physical protection and attenuates ant aggression toward lacewing larvae on ant-tended aphid colonies.     

A developmental variant of indentation in the scales of female cones of Cupressus sempervirens L.

A developmental variant, in which the contact zone between female cone scales is ectopically expressed in many female cones of Cupressus sempervirens , is common in trees growing in Israel. There are two phenotypes: type A with grooves emerging from the contact zone between two scales, and type B with a blind groove in the inner area of a scale. Some scales show a combination of both. These structures are formed constantly, but in different proportions in individual cones, trees and populations. Within the cone, more ectopic indentations are found in the basal scales. The female cones of other members of the Cupressaceae examined, namely Cupressus macrocarpa, C. arizonica and Thuja orientalis , did not have ectopic indentations.     

Costs and benefits of ant attendance to the drepanosiphid aphid Tuberculatus quercicola

The defensive effects of ants against aphid predators have been well documented in the mutualistic relationship of aphids and their attending ants. However, it is not clear whether ant attendance has any direct effect on the aphids' growth and reproduction. Through field experiments, this study evaluates the benefits and, in particular, the costs of ant attendance to aphid colonies, focusing on the drepanosiphid aphid Tuberculatus quercicola which is associated with the Daimyo oak, Quercus dentata , and which is always attended by the red wood ant Formica yessensis . Ant attendance was clearly beneficial to the aphid; the exclusion of ants led to a significant increase in the extinction rate of aphid colonies. However, MANOVA and randomized block ANOVA indicated that in colonies continuously attended by ants, aphids had significantly smaller body size and produced a smaller number of embryos than in colonies isolated from ants when they were reared under homogeneous host conditions free from natural enemies. Thus, ant attendance had a negative influence on the growth and reproduction of the aphids, even though it contributed to the greater longevity of the aphid colonies. We hypothesize that ant-attended aphids are under intense selective pressures that act against aphid clones which fail to attract many ants, so that aphids have developed an adaptive mechanism to allocate a larger fraction of resources to the honeydew when they are requested to do so by the ants in order to ensure the ants' consistent visitation.     

Behavioral mechanisms underlying ants' density-dependent deterrence of aphid-eating predators

Density-dependent mutualisms have been well documented, but the behavioral mechanisms that can produce such interactions are not as well understood. We investigated interactions between predatory ladybirds and the ant Lasius neoniger, which engages in a facultative association with the aphid Aphis fabae . We found that ants disrupted predator aggregation and deterred foraging, but that this effect varied with aphid density. In the field, smaller aphid colonies had higher numbers of ants per aphid (higher relative ant density), whereas plants with larger aphid colonies had lower relative ant density. Ants deterred ladybird foraging when relative ant density was high, but when relative ant density was low, ladybirds aggregated to aphids and foraged more successfully. This difference in ladybird foraging success appeared to be driven by variation in the ants' distribution on the plant and the ladybirds' reaction to ants. When relative ant density was high, ants moved around the perimeter of the aphid colonies, which resulted in faster detection of predators and a greater likelihood of ladybirds leaving. However, when relative ant density was low, ants moved only in the midst of the aphid colonies and rarely around the perimeter, which allowed predators to approach the aphid colony from the perimeter and feed without detection. Such predators were less likely to leave the aphid colony when subsequently detected by ants. We suggest that differences in relative ant numbers, ant distribution, and predator reaction to detection by ants could lead to complex population-level consequences including density-dependent mutualisms and the possibility that predators act as prudent predators.     

Trail system in red wood ants (<Emphasis Type="Italic">Formica rufa</Emphasis> Group) under recreation press

The influence of recreation press on the forager trail system in red wood ants was examined. The model settlement of these ants was situated in green moss-pine forest, comprising areas with a different degree of the recreation press. In 2007, trail systems of 36 anthills were mapped (a total of 136 trails). In 2009, two nests from each group at each digression stage were selected as model objects. These nests possessed close to average values of the cupola diameter (d) and the number of trophic trails (n _c ). In these 6 model nests, trail systems (a total of 33 trails) were re-mapped and the strength of columns was estimated. It had been found that the recreation press decreases the population number in families of red wood ants. Trophic trails become shorter, their structure is simplified, and the number of trees with aphid colonies decreases. When the size of the family decreases owing to irregular decrease in the population number of separate columns, columns possessing non-ramified (less “efficient”) trails disappear first. Weakening of the family decreases the mobility of the trail network; trees with aphid colonies become more important.     

Effects of habitat fragmentation on the three-way interaction among ants,aphids and larvae of the giant purple emperor, <Emphasis Type="Italic">Sasakia charonda</Emphasis> (Hewitson), a near-threatened butterfly

Survival rates of both early and middle instar larvae of the nymphalid butterfly, Sasakia charonda, were estimated to be lowest on test trees planted in a meadow (site A), intermediate in a small, narrow secondary deciduous broadleaf forest (small patch, site B) and highest in a large secondary deciduous broadleaf forest (large forest, site C). The larval mortality rates due to predation by tree-climbing predators from the ground (tree climbing predator) such as ants and the larvae of carabids were estimated to be greater at sites A and B than those at site C. The number of predatory ants climbing test trees was significantly greater at sites A and B than at site C, and the ants harvested honeydew from aphids living on tree leaves at those two sites. Aphid densities were significantly higher on trees at sites A and B than at site C, and aphid densities and numbers of predatory ants were significantly and positively correlated at sites A and B. In an experiment controlling aphid density per branch on test trees, the numbers of ants and the mortality rates of S. charonda larvae were greater on branches with high aphid densities than on those with low aphid densities at both sites A and B. These results suggest that the aphid density per host tree was higher in the meadow and the small patch than in the large forest; at both sites these higher aphid densities attracted higher numbers of predatory ants to test trees, and as a result, mortality rates of S. charonda larvae were increased.     

Progressive sensitivity of trophic levels to warming underlies an elevational gradient in ant–aphid mutualism strength

Although species interactions are often proposed to be stronger at lower latitudes and elevations, few studies have evaluated the mechanisms driving such patterns. In this study, we assessed whether, and by which mechanisms, abiotic changes associated with elevation altered the outcome of an ant–aphid protection mutualism. To do so, we characterized the multi‐trophic interactions among the ant Formica podzolica, the aphid Aphis varians, and aphid natural enemies occurring on the plant Chamerion angustifolium within replicate high and low elevation valleys. Low (versus high) elevation sites had longer summers (snowmelt 13 days earlier) and were on average 1.1°C warmer and 41% drier throughout the year. At low elevations, individual ant colonies consumed approximately double the volume of carbohydrate baits, likely due to a higher foraging tempo, and possibly due to a greater demand for sugar‐ versus protein‐rich resources (as indicated by stable isotope analysis). Wild aphid colonies at low elevations were visited by 1.4‐fold more natural enemies (controlling for variation in aphid abundance), while experimental aphid colonies on potted plants were tended 52% more frequently by ants. As a result, ants increased aphid colony survival by 66% at low elevations but had no detectable effect at high elevations; at low (versus high) elevations aphid colonies without ants had lower survival, demonstrating stronger predator effects, while aphid colonies with ants had higher survival, demonstrating even stronger ant benefits. Analyses for the effects of mean summer temperature yielded qualitatively identical results to those based on elevation. Collectively, these findings support predictions for a greater sensitivity of higher trophic levels to warming and demonstrate how species interactions can vary across environmental gradients due to simultaneous changes in species traits and abundances across multiple trophic levels.     

Leaf nutrient content and host plant selection by leaf-cutter ants, Atta laevigata, in a Neotropical savanna

The selection of nutrient-rich leaves by leaf-cutter ants ( Atta spp.) is thought to be of indirect benefit to these ants by promoting the growth of their symbiotic fungus. However, relatively few studies have analyzed the influence of leaf nutrient content on host plant selection by leaf-cutter ants, and conflicting results have been found. We compared the content of eight nutritional elements plus the non-nutrient aluminum between leaves harvested by colonies of Atta laevigata (Smith) (Hymenoptera: Formicidae: Attini) and leaves collected randomly within their foraging areas. In addition, we evaluated whether leaf nutrient content explained the frequency with which these ants attacked and defoliated some of the tree species found in the study area. For 2 years, we monitored 17–26 trees from 15 species and determined the number of times each plant was attacked and the amount and type of foliage removed. Leaves harvested by A. laevigata presented significantly higher concentrations of N, P, K, Zn, and Cu than those collected randomly. This result is likely to reflect the foraging pattern presented by these ants, which were selective both in terms of the plant species and age of leaves most commonly attacked. Young leaves were the only or the main leaf type exploited in many species, and in comparison to mature leaves these presented significantly higher concentrations of P and K. Large differences in the mean number of ant attacks on the tree species studied were also observed, and those presenting more leaf N tended to be the most frequently attacked.     

Are ant-aphid associations a tritrophic interaction? Oleander aphids and Argentine ants

Summary Oleander aphids, (Aphis nerii), which are sporadically tended by ants, were used as a moded system to examine whether host plant factors associated with feeding site influenced the formation of ant-aphid associations. Seasonal patterns of host plant utilization and association with attendant ants were examined through bi-weekly censuses of the aphid population feeding on thirty ornamental oleander plands (Nerium oleander) in northern California in 1985 and 1986. Colonies occurred on both developing and senescing plant terminals, including leaf tips, floral structures, and pods. Aphids preferentially colonized leaf terminals early in the season, but showed no preference for feeding site during later periods. Argentine ants (Iridomyrmex humilis) occasionally tended aphid colonies. Colonies on floral tips were three to four times more likely to attract ants than colonies on leaf tips, even though the latter frequently contained more aphids. Ants showed a positive recruitment response to colonies on floral tips, with a significant correlation between colony size and number of ants. There was no recruitment response to colonies on leaf tips. These patterns were reproducible over two years despite large fluctuations in both aphid population density and ant activity. In a laboratory bioassay of aphid palatability, the generalist predator,Hippodamia convergens, took significantly more aphids reared on floral tips compared to those reared on leaf tips. The patterns reported here support the hypothesis that tritrophic factors may be important in modifying higher level arthropod mutualisms.     

Do aphids actively search for ant partners?

The aphid–ant mutualistic relationships are not necessarily obligate for neither partners but evidence is that such interactions provide them strong advantages in terms of global fitness. While it is largely assumed that ants actively search for their mutualistic partners namely using volatile cues; whether winged aphids (i.e., aphids’ most mobile form) are able to select ant‐frequented areas had not been investigated so far. Ant‐frequented sites would indeed offer several advantages for these aphids including a lower predation pressure through ant presence and enhanced chances of establishing mutuaslistic interactions with neighbor ant colonies. In the field, aphid colonies are often observed in higher densities around ant nests, which is probably linked to a better survival ensured by ants’ services. Nevertheless, this could also result from a preferential establishment of winged aphids in ant‐frequented areas. We tested this last hypothesis through different ethological assays and show that the facultative myrmecophilous black bean aphid, Aphis fabae L., does not orientate its search for a host plant preferentially toward ant‐frequented plants. However, our results suggest that ants reduce the number of winged aphids leaving the newly colonized plant. Thus, ants involved in facultative myrmecophilous interactions with aphids appear to contribute to structure aphid populations in the field by ensuring a better establishment and survival of newly established colonies rather than by inducing a deliberate plant selection by aphid partners based on the proximity of ant colonies.     

Elevated temperatures alter an ant‐aphid mutualism

Ant‐hemipteran mutualisms are keystone interactions that can be variously affected by warming: these mutualisms can be strengthened or weakened, or the species can transition to new mutualist partners. We examined the effects of elevated temperatures on an ant‐aphid mutualism in the subalpine zone of the Rocky Mountains in Colorado, USA. In this system, inflorescences of the host plant, Ligusticum porteri Coult. & Rose (Apiaceae), are colonized by the ant‐tended aphid Aphis asclepiadis Fitch or less frequently by the non‐ant tended aphid Cavariella aegopodii (Scopoli) (both Hemiptera: Aphididae). Using an 8‐year observational study, we tested for two key mechanisms by which ant‐hemipteran mutualisms may be altered by climate change: shifts in species identity and phenological mismatch. Whereas the aphid species colonizing the host plant is not changing in response to year‐to‐year variation in temperature, we found evidence that a phenological mismatch between ants and aphids could occur. In warmer years, colonization of host plant inflorescences by ants is decreased, whereas for A. asclepiadis aphids, host plant colonization is mostly responsive to date of snowmelt. We also experimentally established A. asclepiadis colonies on replicate host plants at ambient and elevated temperatures. Ant abundance did not differ between aphid colonies at ambient vs. elevated temperatures, but ants were less likely to engage in tending behaviors on aphid colonies at elevated temperatures. Sugar composition of aphid honeydew was also altered by experimental warming. Despite reduced tending by ants, aphid colonies at elevated temperatures had fewer intraguild predators. Altogether, our results suggest that higher temperatures may disrupt this ant‐aphid mutualism through both phenological mismatch and by altering benefits exchanged in the interaction.     

Host-plant selection,diet diversity,and optimal foraging in a tropical leafcutting ant

Summary A month-long study was conducted on the comparative foraging behavior of 20 colonies of the leafcutting ant, Atta cephalotes L. in Santa Rosa National Park, Guanacaste Province, Costa Rica. The study was conducted during the middle of the wet season, when trees had mature foliage and the ants were maximally selective among species of potential host plants. The colonies always gathered leaves from more than a single tree species but on average one species constituted almost half the diet with the remaining species being of geometrically decreasing importance. Colonies exhibited greater diversity in their choice of leaves and lower constancy of foraging when the average quality of resource trees was lower, as predicted by elementary optimal foraging theory. Furthermore, the ants were more selective of the species they attacked at greater distances from the nest. However, the ants sometimes did not attack apparently palatable species, and often did not attack nearby individuals of species they were exploiting at greater distances.A classical explanation for why leafcutting ants exploit distant host trees when apparently equally good trees are nearer, is that the ants are pursuing a strategy of conserving resources to avoid long-term overgrazing pressure on nearby trees. We prefer a simpler hypothesis: (1) Trees of exploited species exhibit individual variation in the acceptability of their leaves to the ants. (2) The abundance of a species will generally increase with area and radial distance from the nest, so the probability that at least one tree of the species will be acceptable to the ants also increases with distance. (3) The ants forage using a system of trunk-trails cleared of leaf litter, which significantly reduces their travel time to previously discovered, high-quality resource trees (by a factor of 4- to 10-fold). (4) Foragers are unware of the total pool of resources available to the colony. Therefore once scouts have chanced upon a tree which is acceptable, the colony will concentrate on harvesting from that tree rather than searching for additional sources of leaves distant from the established trail.     

Cornicle length in Macrosiphini aphids: a comparison of ecological traits

Abstract 1. Aphids often emit cornicle droplets when attacked by predators. While the function of cornicle droplets has long been debated (i.e. mechanical protection vs. chemical signalling), it is not understood why aphid species have cornicles of different lengths.
2. It was hypothesised that aphids living in more scattered colonies have longer cornicles to scent-mark predators with cornicle droplets containing alarm pheromone, so that clone-mates are provided with advanced warning of a threat, even if not at the predation site. To test this hypothesis, multiple regression analyses were used, due to a lack of phylogenetic information on these taxa, to address which ecological traits (amount of wax on an aphid, degree of colony aggregation, feeding shelter, ant attendance) are correlated with cornicle length.
3. Aphids living in dense colonies tended to have shorter cornicles than aphids living in more scattered colonies. Also, aphids with more protection (i.e. wax) on their bodies had shorter cornicles. Aphids also tended to have shorter cornicles when tended by ants. The presence of a feeding shelter was not a good predictor of cornicle length.
4. It is suggested that longer cornicles function to scent-mark predators with alarm pheromone to increase the inclusive fitness of a clone; however the negative correlation between the amount of individual protection, and also ant attendance, and cornicle length argues for a trade-off between different forms of defence.     

Effects of ant exclusion during outbreaks of a defoliator and a sap-sucker on birch

1. The influence of a wood ant, Formica aquilonia, on the defoliation of the white birch, Betula pubescens, and on its invertebrate community was studied in ant-exclusion experiments during two outbreaks, the decline phase of the autumnal moth, Epirrita autumnata, and the peak year of the birch aphid, Euceraphis punctipennis, not tended by ants. 2. The numbers of the wood ant and Symydobius oblongus, a tended aphid, in birch foliage showed a strong positive correlation, and the former decreased rapidly when the distance from the ant mound increased, confirming that there was a distance-related gradient in arboreal ant predation. There may have been a parallel reduction in soil amelioration by ants through nest construction and food gathering. 3. The application of a glue ring around the trunk excluded ants totally from the canopy, inhibiting predation but not fertilization. 4. Ant-exclusion resulted in a 90–95% reduction in the growth of tended aphid colonies by mid-season. 5. Outbreak populations of the autumnal moth and the birch aphid were reduced by 45–67% and 77%, respectively, in control trees and correlated negatively with ant numbers. 6. The total percentage of leaf area damaged by moth larvae was 34% lower in ant-foraged than in unforaged trees. 7. Neither the distance from the ant mound nor its interaction with the glue treatment had any effect on the herbivores or folivory, indicating that the possible soil-ameliorating effect was weaker than predation, which reduced herbivore numbers at every distance studied (4–20 m). 8. Predation by ants also affected the abundance of syrphid larvae, predatory on both aphids, the percentage parasitism by a wasp, Aleiodes testaceus, on the autumnal moth, and thereby (or directly) its age (size) distribution. The presence of ants had no influence on spider abundance. 9. It is concluded that predation rather than soil amelioration is likely to be the reason why the degree of folivory and, during serious outbreaks, the mortality of trees are lower in the vicinity of wood-ant mounds.     

Aphid-ant interaction reduces chrysomelid herbivory in a cottonwood hybrid zone

In a cottonwood (Populus) hybrid zone, Chaitophorus aphids attract aphid-tending ants which subsequently reduce herbivory by the leaf-feeding beetle, Chrysomela confluens. Observations and experimental manipulations of aphids and beetle larvae on immature cottonwood trees demonstrated that: 1) via their recruitment of ants, aphids reduced numbers of beetle eggs and larvae on the host; 2) these interactions occurred within a few days of the host being colonized by aphids; and 3) although aphid colonies were ephemeral, their presence resulted in a 2-fold reduction in beetle herbivory. The aphid-ant interaction is most important in the hybrid zone where 93% of the beetle population is concentrated (for reasons unrelated to aphids and ants). Because beetle defoliation of immature trees is high (ca. 25%), the indirect effect of aphids in reducing herbivory is likely more beneficial to trees in the hybrid zone than in adjacent pure zones where beetle herbivory is virtually absent. Tree genotype likely affects the impact of the aphid-ant interaction on trees within the hybrid zone, since levels of herbivory differ between sympatric Fremont and hybrid cottonwoods.     

Getting carbohydrates in ants: damage of the young cereal sprouts by ants of the genus Myrmica Latreille, 1804 (Hymenoptera: Formicidae), to obtain plant sap

Summary

Carbohydrate food is of high importance for survival of ant colonies. Ants are known to use sugary excretions (honeydew) of various insects, nectar of floral and extrafloral nectaries, and even sap of some trees. However, the ability of ants to use sap of herbaceous plants has not been mentioned. This is the first evidence that ants of the genus Myrmica can intentionally ‘cut off’ young cereal sprouts to obtain plant sap. The investigation was carried out in a laboratory in 2018 and 2019 and involved three ant species of the genus Myrmica [12 colonies of M. rubra (Linnaeus, 1758); eight colonies of M. ruginodis Nylander, 1846; and five colonies of M. scabrinodis Nylander, 1846]. First observations were made occasionally in 10 ant colonies during the study of ant–aphid interactions. After three days of carbohydrate starvation, ants were supplied with the plants of wheat infested with aphids of Schizaphis graminum (Rondani, 1852). Within the first day in addition to ordinary trophobiotic relations with aphids, the workers of all the studied colonies demonstrated unexpected behaviour: they ‘cut off’ some sprouts and collected sap of these plants. The experimental investigation in 15 ant colonies of various sizes (about 150, 300 and 500 workers) supplied with the plants infested or non-infested with aphids has shown that getting sap of herbs depends greatly on ant colony needs and available resources. The number of damaged plants was much higher both in the larger colonies of ants and in the absence of aphids. This way of getting carbohydrates allows ants to quickly obtain some extra food needed to maintain colony viability and seems to be one of the mechanisms promoting survival of ants in conditions of acute carbohydrate deficiency. At the same time, ants avoid using plant sap when there are more available alternative carbohydrate resources.     

The unusual social organization of the antPachycondyla tridentata (Formicidae,ponerinae)

Colonies of the ponerine antPachycondyla tridentata from Malaysia occur with and without queens. In a total of 7 colonies we found more than 80% of the workers to be mated, irrespective of the presence or absence of queens. This is a hitherto unknown social organisation in ants. Queens and workers competed equally for reproduction. In the colonies investigated several ants were laying eggs. Behavioral observations revealed persistent dominance interactions between colony members. A few ants, but not necessarily a queen, occupied top positions. Removal of the most dominant ants led to a new hierarchy in which subordinate ants with developed ovaries were attacked significantly more frequently than non-reproductive ants. On the average, callows were more aggressive than older subordinate ants, displacing most of the older laying workers in one colony. Nestmate recognition tests revealed that non-reproductive ants were much more aggressive towards foreign ants than were ants with developed ovaries.     

Ant–aphid mutualism: the influence of ants on the aphid summer cycle

There are few longtime studies on the effects on aphids of being tended by ants. The aim of this study is to investigate how the presence of ants influences settling decisions by colonizing aphids and the post‐settlement growth and survival of aphid colonies. We conducted a field experiment using the facultative myrmecophile Aphis fabae and the ant Lasius niger. The experiment relied on natural aphid colonization of potted plants of scentless mayweed Tripleurospermum perforatum placed outdoors. Ants occurred naturally at the field site and had access to half of the pots and were prevented from accessing the remainder. The presence of winged, dispersing aphids, the growth and survival of establishing aphid colonies, and the presence of parasitoids were measured in relation to presence or absence of ants, over a period of five weeks. The presence of ants did not significantly influence the pattern of initial host plant colonization or the initial colony growth, but ant‐tended aphids were subject to higher parasitism by hymenopteran parasitoids. The net result over the experimental period was that the presence of ants decreased aphid colony productivity, measured as the number of winged summer migrants produced from the colonized host plants. This implies that aphids do not always benefit from the presence of ants, but under some conditions rather pay a cost in the form of reduced dispersal.