Maculinea Alcon Research Articles

An unexpected record of Myrmica schencki EMERY, 1895 as a secondary host ant of the hygrophilous form of a small and isolated population of the Alcon Blue butterfly Phengaris (=Maculinea) alcon (DENIS et SCHIFFERMÜLLER, 1775) (Lepidoptera, Lycaenidae) in NE Poland

Abstract Phengaris alcon is a socially parasitic butterfly species showing ecological variation across its distribution range. Host ant specificity was studied on a site (a mineral island surrounded by wetlands) in the Narew National Park in NE Poland, inhabited by a highly isolated and small population (estimated at several dozen individuals). We examined nests of their potential hosts, i.e. Myrmica ants, in patches of habitat where the initial larval food plant i.e. Gentiana pneumonanthe was recorded. The Myrmica species composition was shown to be unusual for such habitats because of the presence of M. schencki together with the dominant M. scabrinodis. In 2013 we found just one prepupa of P. alcon in a nest of M. schencki, which had never yet been recorded as a host of the hygrophilous form of this butterfly, and none of the M. scabrinodis nests were infested. However, in 2014 a very typical pattern for eastern Europe was observed, i.e. larvae were recorded exclusively in M. scabrinodis colonies and the parasitisation rate was 33%. In both seasons we recorded similar numbers of egg shells on gentians, which indicated a similar population size of adult butterflies. The results are discussed in the context of the ecology and conservation of P. alcon as well as the sampling design.

Phengaris (Maculinea) alconbutterflies deposit their eggs on tall plants with many large buds in the vicinity ofMyrmicaants

AbstractThe survival of eggs and larvae is dependent on the oviposition site selection of their mothers. In obligate myrmecophilic butterflies, both host plant phenology and host ant presence are expected to affect the decision where to deposit eggs. The importance of ant nest presence in the oviposition site selection ofPhengarisbutterflies is, however, highly debated.We studied oviposition in the largestPhengaris (Maculinea) alconpopulation in Portugal, exploitingGentiana pneumonantheas the host plant andMyrmica alobaas host ant. We collected phenological plant data and recorded the presence and number of eggs on plants with and withoutMyrmicaants nearby during the flight period of the butterfly.Females oviposited on tall plants with many tall buds, while the presence of host ant nests weakly affected oviposition on plants where the probability of finding ants at close range was high. Moreover, larger plants with many tall buds close to host ant nests received more eggs.A density‐dependent shift in oviposition was not found as the proportion of buds not infected with eggs did not differ between plants with or without ants, whereas plant characteristics did have an effect. Tall plants with many large buds were associated with earlier oviposition.Our results suggest that females ofP. alconin Portugal choose gentian plants for oviposition mainly based on plant characteristics whereas the vicinity of ants had a weak effect. Moreover, our study shows that testing the ant‐mediated oviposition hypothesis requires baiting ants more than once.

Influence of host plant phenology and oviposition date on the oviposition pattern and offspring performance of the butterfly Phengaris alcon

The timing of oviposition and selection of the phenological stage of the host plant can have significant consequences for development and success of offspring, and is particularly important for endangered specialist species with rare habitats, such as Phengaris alcon butterflies. Females of this species oviposit on marsh gentians, Gentiana pneumonanthe. For the first time, we evaluate the survival of eggs deposited by early and late flyers in relation to the phenological stage of marsh gentian flower buds, as well as caterpillar survival and development. An analysis was conducted on 127 gentian shoots, on which 837 eggs were monitored. We observed more frequent oviposition on the apical and youngest buds, with increased egg load by females during the first one-third of the flight period. Offspring survival of about 55 % was observed, with up to 15 caterpillars per bud. Offspring survival was significantly higher from eggs that were oviposited on larger flower buds and on flower buds in an early developmental stage. Also, early flyers’ offspring gave rise to better survival rates and the caterpillar development in flower buds differed significantly according to bud size, with more days required in smaller buds. Finally, the significant differences found across the entire study period illustrate that the understanding of oviposition through time is important to the conservation of this rare European species.

The re-discovered Maculinea rebeli (Hirschke, 1904): Host ant usage, parasitoid and initial food plant around the type locality with taxonomical aspects (Lepidoptera, Lycaenidae).

The taxonomy of the myrmecophilous Maculinea alcon group (Lepidoptera: Lycaenidae) is highly debated. The host-plant and host-ant usage of these butterflies have conventionally been important in their identification. Maculinea ‘rebeli’ has generally been considered to be the xerophilous form of Ma. alcon (Ma. alcon X hereafter) with Gentiana cruciata as initial food plant. However, the type locality and all other known sites of Ma. rebeli are found above the coniferous zone, and are well separated from the lower regions where Ma. alcon X sites are found. Furthermore, no food plant and host ant data for the nominotypic Ma. rebeli have yet been published. Our aim was therefore to identify the host ant(s) of Ma. rebeli around the type locality and compare this with the host ant usage of nearby Ma. alcon X. Nests of Myrmica spp. (Hymenoptera: Formicidae) close to the host plants were opened on one Ma. alcon X (host plant: Gentiana cruciata) and two Ma. rebeli (host plant: Gentianella rhaetica, first record, confirmed by oviposition and emerging larvae) sites just before the flying period, to find prepupal larvae and pupae. Three Myrmica species (My. lobulicornis, My. ruginodis, My. sulcinodis) were found on the two Ma. rebeli sites, which parasitized exclusively My. sulcinodis (22 individuals in 7 nests). On the Ma. alcon X site Myrmica sabuleti and My. lonae were found, with My. sabuleti the exclusive host (51 individuals in 10 nests). Ichneumon cf. eumerus parasitized both butterflies. The results highlight the differentiation of Maculinea rebeli from Ma. alcon X, from both conservation biological and ecological points of view. Thus, it should be concluded that Ma. rebeli does not simply represent an individual form of Ma. alcon but it can be considered as at least an ecological form adapted to high mountain conditions both in its initial food plant and host ant species. In addition, it should be emphasized that Ma. alcon X (= Ma. rebeli auct. nec Hirschke) cannot be synonymised with Ma. rebeli (Hirschke, 1904).

Myrmica aloba (Hymenoptera: Formicidae) hosts isolated populations of a hoverfly, a butterfly and an ichneumon species in NE-Portugal

Larvae and pupae of the obligately myrmecophilous social parasites Microdon myrmicae (Diptera: Syrphidae) and Maculinea alcon (Lepidoptera: Lycaenidae) were found using exclusively Myrmica aloba (Hymenoptera: Formicidae) host ants in NE-Portugal. Ichneumon eumerus (Hymenoptera: Ichneumonidae) was also found developing in Ma. alcon pupae in nests of My. aloba at the same site. These are the first records of Mi. myrmicae and I. eumerus for Portugal, and from My. aloba nests. Earlier records that My. aloba is the only known host ant of Ma. alcon in Portugal are confirmed. Further studies on the biology of these isolated peripheral populations are necessary for their well-planned protection.

Differences in oviposition strategies between two ecotypes of the endangered myrmecophilous butterfly Maculinea alcon (Lepidoptera: Lycaenidae) under unique syntopic conditions

Abstract The Alcon Blue Maculinea alcon and the Mountain Alcon Blue Maculinea ‘rebeli’ are obligate ant‐parasitic butterflies with no distinct morphological and genetic differences but clear ecological separation. The two butterflies generally lay their eggs on distinct host plant species: M. alcon on Gentiana pneumonanthe and M. ‘rebeli’ on Gentiana cruciata. The egg‐laying behaviour of these two ecotypes has previously only been investigated in sympatric, but not in syntopic populations. We studied the egg‐laying preferences of M. alcon and M. ‘rebeli’ in a unique area where they co‐occur, and where they use different host plants. The distance to the nearest other host plant does not seem to influence the decision of female butterflies as to whether to lay eggs on a specific host plant. The two butterflies laid their eggs on different parts of their host plants: M. alcon preferred the sepals of G. pneumonanthe flower buds, while M. ‘rebeli’ laid most eggs on the leaves of G. cruciata. The major factor correlated with the number of eggs laid on the host plant seemed to be plant quality (number of flowers, stem length, etc.) for both butterflies. The present study reveals behavioural differences between the two Alcon Blue forms under unique syntopic conditions, a hidden intraspecific diversity that is worth conserving.

Interspecific relationships in co-occurring populations of social parasites and their host ants

Myrmica ant colonies host numerous insect species, including the larvae of Maculinea butterflies and Microdon myrmicae hoverflies. Little is known about the interspecific relationships among these social parasites and their host ants occurring in sympatric populations. We investigated communities of social parasites to assess the strategies allowing them to share the same pool of resources (i.e. Myrmica colonies). The present study was carried out at five sites inhabited by different social parasite communities, each comprising varying proportions of Maculinea teleius, Maculinea nausithous, Maculinea alcon, and Microdon myrmicae. We investigated their spatial distributions, host segregation, the degree of chemical similarity between social parasites and hosts, and temporal overlaps in colony resource exploitation. Spatial segregation among social parasites was found in two populations and it arises from microhabitat preferences and biological interactions. Local conditions can drive selection on one social parasite to use a Myrmica host species that is not exploited by other social parasites. Myrmica scabrinodis and Myrmica rubra nests infested by larvae of two social parasite species were found and the most common co-occurrence was between Ma. teleius and Mi. myrmicae. The successful coexistence of these two species derives from their exploitation of the host colony resources at different times of the year. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 699–709.

Relationship between the butterfly Phengaris rebeli and its larval host plant Gentiana cruciata in Lithuanian population

Relationship between the endangered herbaceous plant Gentiana cruciata and its specialist herbivore, the endangered butterfly Alcon Blue, Phengaris rebeli, was studied in Lithuanian population which is the northernmost one over the whole known species range in Europe. The size of P. rebeli population was estimated basing on eggshell counts on the larval host plant. Oviposition behaviour of P. rebeli was investigated during summer season of 2011 on a grassland area in Neris Regional Park, Lithuania. Potential host plants were checked and eggshells of P. rebeli were counted. A total of 619 eggshells were counted on 248 out of 536 G. cruciata stems checked. Selective choice of both host plants and site for oviposition on host plant was revealed. Approximately 89% eggs were laid on the organs of the uppermost whorl. Plants selected by females for oviposition almost always had a luxuriant growth and most of them were higher than the surrounding vegetation.

Host plant-mediated effects of climate change on the occurrence of the Alcon blue butterfly (Phengaris alcon)

Among the expected consequences of climate change are shifts in species’ ranges. Most of current methods to predict such shifts in species distributions consider changes in suitability of climatic conditions for existence. With these models, it is possible to indicate the potential distribution of species that would arise under spatial conditions that cause unlimited landscape accessibility and habitat suitability. At the regional scale, however, detailed predictions of changes in species distributions and performance are pivotal for conservation planning. This study aims to predict species occurrences at the regional scale, incorporating demographic processes and dispersal to assess habitat accessibility and suitability in detail. We investigated a system with trophic dependence: the Alcon blue butterfly (Phengaris alcon) is fully dependent on the occurrence of its host plant species marsh gentian (Gentiana pneumonanthe). We applied a model chain, consisting of a soil and biomass model, a plant species occurrence and dispersal model and a butterfly metapopulation model. We investigated the effect of future climate change, both under affected and unaffected habitat conditions as determined by host plant occurrence. Our modelled results show that the butterflies perform best when habitat conditions remain unaffected by climate change. However, when climate change does affect the occurrence of its host plant species, butterfly distribution and performance will be deteriorated. This implies that detailed predictions of changes in species distributions and performance should incorporate dispersal, demographic processes and biotic interactions explicitly. Our approach allows for the identification of locations that are potentially suitable for the measures increasing network robustness for P. alcon.

Discovery of isolated populations of Phengaris alcon and of Melitaea diamina in the central Po Plain, Italy (Lepidoptera Rhopalocera)

Riassunto - Scoperta di popolazioni isolate di Phengaris alcon e Melitaea diamina nella Pianura Padana centrale (Italia) (Lepidoptera Rhopalocera). all’interno del Parco del Mincio (Mantova, lombardia) sono state scoperte popolazioni di Melitaea diamina (Lang, 1789) e Phengaris alcon ([Denis & Schiffermueller], 1775) (lepidoptera rhopalocera), rispettivamente nell’anno 2008 e 2010. entrambe le specie non sono note per la Pianura Padana, e le popolazioni più vicine conosciute si trovano a 170 e 50 km, rispettivamente per P. alcon e M. diamina. Durante l’anno 2011 sono state svolte ulteriori indagini su queste nuove popolazioni. entrambe le specie sono state riscontrate esclusivamente in prati umidi, di cui sono considerate specie tipiche. le nuove popolazioni dovranno essere protette, garantendo il mantenimento in futuro dei prati umidi mediante sfalcio.Abstract - Populations of Melitaea diamina (Lang, 1789) and Phengaris alcon ([Denis & Schiffermueller], 1775) (lepidoptera rhopalocera) were discovered in the Mincio natural Park (Mantua province, lombardy) in the years 2008 and 2010, respectively. Both species had not been known from the central Po Plain and the closest populations are approximately 170 km and 50 km away for P. alcon and M. diamina, respectively. More data on the new populations were collected during the year 2011. Both species were exclusively found in wet meadows, for which they are considered typical. The newly discovered populations need to be protected by ensuring that the meadows will continue to be mown in the future.

Life cycle and growth pattern of the endangered myrmecophilous Microdon myrmicae (Diptera: Syrphidae)

In Europe there are only a few species of the syrphid fly Microdon, which live in the nests of various genera of ants. For most of these rare flies, details of their biology, larval behaviour and relationships with their hosts are still not yet well known. In this paper we present data on the life cycle, feeding behaviour and growth pattern of Microdon myrmicae, a social parasite of Myrmica ants and compare it with two species of Maculinea butterflies similarly parasitizing Myrmica ant colonies. M. myrmicae has three larval instars and overwinters as a third instar. Eggs and 1st instar larvae are ignored by ants, which indicate that they are "chemically insignificant". 2nd and 3rd instar larvae feed on small ant brood. M.myrmicae larvae grow rapidly from May to July and later in the year the host colony only serves as shelter for overwintering. Like Maculinea alcon, larvae of M. myrmicae are numerous in Myrmica nests and more numerous than those of Maculinea teleius. Since the larvae of Microdon feed on an abundance of young ant brood, they experience low level of scramble competition and although many may develop in an ant's nest they have probably little effect on host colony fitness.

Spatially and Financially Explicit Population Viability Analysis of Maculinea alcon in The Netherlands

BackgroundThe conservation of species structured in metapopulations involves an important dilemma of resource allocation: should investments be directed at restoring/enlarging habitat patches or increasing connectivity. This is still an open question for Maculinea species despite they are among the best studied and emblematic butterfly species, because none of the population dynamics models developed so far included dispersal.Methodology/Principal FindingsWe developed the first spatially and financially explicit Population Viability Analysis model for Maculinea alcon, using field data from The Netherlands. Implemented using the RAMAS/GIS platform, the model incorporated both local (contest density dependence, environmental and demographic stochasticities), and regional population dynamics (dispersal rates between habitat patches). We selected four habitat patch networks, contrasting in several basic features (number of habitat patches, their quality, connectivity, and occupancy rate) to test how these features are affecting the ability to enhance population viability of four basic management options, designed to incur the same costs: habitat enlargement, habitat quality improvement, creation of new stepping stone habitat patches, and reintroduction of captive-reared butterflies. The PVA model was validated by the close match between its predictions and independent field observations on the patch occupancy pattern. The four patch networks differed in their sensitivity to model parameters, as well as in the ranking of management options. Overall, the best cost-effective option was enlargement of existing habitat patches, followed by either habitat quality improvement or creation of stepping stones depending on the network features. Reintroduction was predicted to generally be inefficient, except in one specific patch network.Conclusions/SignificanceOur results underline the importance of spatial and regional aspects (dispersal and connectivity) in determining the impact of conservation actions, even for a species previously considered as sedentary. They also illustrate that failure to account for the cost of management scenarios can lead to very different conclusions.

The habitat vegetational structure and the success of the blue alcon, Maculinea alcon (Denis & Schiffermüller)

In the present work, we report the first reference for blue alcon, Maculinea alcon (Denis & Schiffermüller) (Lepidoptera, Lycaenidae), in Portugal. This butterfly species maintains a complex relationship with its host plant marsh gentian (Gentiana pneumonanthe L., Gentianaceae) and with Myrmica ants in its habitat in Northern Portugal. This study involved a multivariate analysis of the relationship between M. alcon and selected habitat variables aimed at proposing a suitable methodology for the conservation of this species. Three habitats were distinguished in terms of their floristic combinations: density of ferns (more humid and deep soils, Habitat A), size of grasses (left wetlands, Habitat B) and shrubs (productive wetland, Habitat C). In these habitats, several G. pneumonanthe and M. alcon parameters were recorded as well as the number of host ant nests. Taller plants and higher number of Maculinea eggs were observed in the habitats with higher values ofshrubs and grasses cover (Habitats B and C), whereas the higher number of plants was stimulated by higher values of shrub cover (Habitat C). In contrast, more humid soils and low cattle pressures reduce the density of plants and ant nests and, consequently, the presence of Maculinea. However, the existence of ant nests is decreased under herbaceous layers. These results suggest that the right balance between the number of gentians and Myrmica nests will ensure the survival of theM.alcon butterfly. Thus, the management of the ecosystems where these species occur, i.e. the Erica tetralix hygroscopic communities, requires the maintenance of the balance between the grass and the shrub layers in order to ensure the existence of Myrmica nests and, consequently, the survival of M. alcon.

Differences in genetic variability between two ecotypes of the endangered myrmecophilous butterfly Phengaris (=Maculinea) alcon– the setting of conservation priorities

Abstract. 1. The endangered butterfly Phengaris alcon exists in two ecotypes (P. ‘alcon’ and P. ‘rebeli’), which inhabit contrasting biotopes (wet and warm/dry grasslands respectively) and use different larval food plants. The initially flower‐bud‐feeding caterpillars complete their development as social parasites of Myrmica ants, and the specificity of these relationships shows geographical variation.2. We studied the genetic structure of 16 populations (365 individuals) of both ecotypes in eastern Europe, sampling P. ‘rebeli’ in two disjunct areas in Lithuania and southern Poland, and P. ‘alcon’ on Polish localities between them. We analysed the cytochrome c oxidase subunit I (COI) mitochondrial gene, the EF1‐α nuclear gene and five polymorphic microsatellite loci.3. All individuals shared an identical COI haplotype, which we hypothesise may be linked to a selective sweep associated with the presence of the Wolbachia B strain in all populations.4. For nuclear markers, we did not find a clear pattern reflecting division into two putative ecotypes. However, ecotypes differed significantly in their genetic variability, i.e., the P. ‘rebeli’ ecotype was less polymorphic, and its populations were much more differentiated (FST: 0.632 for EF1‐α and 0.504 for microsatellites) than the P. ‘alcon’ ecotype (0.177 and 0.082, respectively).5. Our microsatellite data suggest that all populations of P. ‘alcon’ form a single clade but that P ‘rebeli’ can be split into either six or two clades. The former model would indicate many independent origins, especially in the mountainous areas of southern Poland. The latter, not mutually exclusive, grouping clearly reflects the use of different host ants.

Survival and growth of parasitic Maculinea alcon caterpillars (Lepidoptera, Lycaenidae) in laboratory nests of three Myrmica ant species

The Alcon blue butterfly (Maculinea alcon) parasitizes the nests of several Myrmica ant species. In Denmark, it uses M. rubra and M. ruginodis, but never M. scabrinodis. To further examine the basis of this specificity and local co-adaptation between host and parasite, the pattern of growth and survival of newly-adopted caterpillars of M. alcon in Myrmica subcolonies was examined in the laboratory. M. alcon caterpillars were collected from three populations differing in their host use, and reared in laboratory nests of all three ant species collected from each M. alcon population. While there were differences in the pattern of growth of caterpillars from different populations during the first few months after adoption, which depended on host ant species and the site from which the ants were collected, there was no evidence of major differences in final size achieved. Survival was, however, much higher in nests of M. rubra than in nests of M. ruginodis and M. scabrinodis, even for caterpillars from a population that is never known to use M. rubra as a host in the field. The caterpillars of M. alcon thus do not show local adaptation in their pattern of growth and survival, but instead show a pattern that may reflect different nestmate recognition abilities of the host ants, related to their sociogenetic organisation. The pattern of observed host ant use in the field seems to result from a combination of differences in local host availability and locally adapted infectivity, modulated by smaller differences in survivorship in the nests of the different host ants.

Myrmecophiles

Myrmecophiles

Egg spreading in the ant-parasitic butterfly, Maculinea alcon: from individual behaviour to egg distribution pattern

Oviposition site selection can be viewed as an act of parental care; it is a life history trait with significant consequences for offspring development and success. Herbivorous insects may adopt different strategies for spreading their eggs (e. g. single oviposition events versus egg clustering). Host plant use results from the interplay of available cues and the responsiveness of the ovipositing female. We studied how egg-laying behaviour of individual females resulted in the egg distribution patterns observed at the population level in the ant-parasitic butterfly Maculinea alcon. Eggs are laid on marsh gentians, Gentiana pneumonanthe, but survival also depends on the presence of Myrmica host ants as young caterpillars leave the host plant and survive only after being adopted by ants. Several studies have focused on egg distribution patterns, but less so on the behavioural mechanisms behind the oviposition patterns. Our observational data show evidence for some level of egg clustering, as predicted by the obligate myrmecophilous lifestyle. There was no evidence of egg-laying avoidance when gentians already carried several eggs. Phenological time windows for oviposition on individual flower buds and gentians were much wider than reported before. Detailed tracking of egg-laying females in the field showed high rates of oviposition and suggest relatively high average levels of fecundity compared to fully herbivorous lycaenid butterflies. Results are discussed in relation to adaptive oviposition strategies of this highly specialist ant parasite of conservation concern. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Maculinea alcon exploits Myrmica aloba in Portugal: unusual host ant species of a myrmecophilous butterfly in a peripheral region

Larvae of the obligate myrmecophilous social parasite Maculinea alcon (Lepidoptera: Lycaenidae) were found exclusively using Myrmica aloba (Hymenoptera: Formicidae) ant hosts in NE-Portugal. This is the first record of the host ant usage of any Maculinea species in Portugal, and of any Maculinea using M. aloba nests. These results on such peripheral European populations confirm that knowledge of the local host ant species is crucial for the successful protection of these endangered butterflies, and vital for examining the evolution of such interactions.

Relative importance of density-dependent regulation and environmental stochasticity for butterfly population dynamics

The relative contribution of density-dependent regulation and environmental stochasticity to the temporal dynamics of animal populations is one of the central issues of ecology. In insects, the primary role of the latter factor, typically represented by weather patterns, is widely accepted. We have evaluated the impact of density dependence as well as density-independent factors, including weather and mowing regime, on annual fluctuations of butterfly populations. As model species, we used Maculinea alcon and M. teleius living in sympatry and, consequently, we also analysed the effect of their potential competition. Density dependence alone explained 62 and 42% of the variation in the year-to-year trends of M. alcon and M. teleius, respectively. The cumulative Akaike weight of models with density dependence, which can be interpreted as the probability that this factor should be contained in the most appropriate population dynamics model, exceeded 0.97 for both species. In contrast, the impacts of inter-specific competition, mowing regime and weather were much weaker, with their cumulative weights being in the range of 0.08-0.21; in addition, each of these factors explained only 2-5% of additional variation in Maculinea population trends. Our results provide strong evidence for density-dependent regulation in Maculinea, while the influence of environmental stochasticity is rather minor. In the light of several recent studies on other butterflies that detected significant density-dependent effects, it would appear that density-dependent regulation may be more widespread in this group than previously thought, while the role of environmental stochasticity has probably been overestimated. We suggest that this misconception is the result of deficiencies in the design of most butterfly population studies in the past, including (1) a strong focus on adults and a neglect of the larval stage in which density-dependent effects are most likely to occur; (2) an almost exclusive reliance on transect count results that may confound the impact of environmental stochasticity on butterfly numbers with its impact on adult longevity.

Oviposition preferences of Maculinea alcon as influenced by aphid (Aphis gentianae) and fungal (Puccinia gentianae) infestation of larval host plants

Abstract 1. The influence of infestation of the larval host plant Gentiana cruciata on the egg‐laying preferences of the xerophilous ecotype of Alcon Blue butterfly (Maculinea alcon) was studied in a semi‐dry grassland area (Aggtelek Karst Region, Northern Hungary).2. We examined whether oviposition patterns of females differed when G. cruciata stems were uninfested compared with when they were infested by an aphid (Aphis gentianae) or a rust (Puccinia gentianae) species.3. Females laid more than 90% of their eggs on fertile, uninfested G. cruciata stems, although these stems comprised only ∼ 50% of the total stems available. Stems infested by aphids were similar to uninfested ones in properties that had a strong correlation with egg numbers, and yet there were significantly fewer eggs on infested stems than on intact ones.4. Females never laid eggs on parts of Gentiana stems infested by aphids, and the presence of Lasius paralienus ants, which have a mutualistic interaction with Aphis gentianae, did not increase the repulsive effect of aphids. Infection of Gentiana by Puccinia did not influence the egg‐laying behaviour of females, even though the flowers and buds of infested stems exhibited a delayed development.5. Aphid infestation can influence butterfly oviposition patterns through both direct and indirect effects. The presence of aphids directly excluded oviposition, but our data also indicated the possibility of an indirect effect of aphid infestation. Stems that had no aphids at the last egg counting, but were infested prior to it, had significantly fewer eggs than those that were never infested.