Individual Host Plants Research Articles

Laboratory evaluation of the life history of hibiscus mealybug, Nipaecocus viridis (Hemiptera: Pseudococcidae), on selected citrus and potential non-citrus hosts in Florida.

Nipaecoccus viridis (Newstead) (Hemiptera: Pseudococcidae) is an emerging invasive pest of citrus. There is no information on the life history of N. viridis in relation to citrus cultivars produced in Florida. Here, we quantified the life-history parameters of N. viridis on 6 citrus and 3 non-citrus host plant species under laboratory conditions. We also investigated the effect of mode of reproduction (sexual vs. parthenogenic) on the fecundity of N. viridis. Nipaecoccus viridis was able to develop to maturity and reproduce on all host plant taxa tested. The individual host plants affected the developmental and survival rate, adult longevity, and offspring production of N. viridis. All citrus genotypes commercially grown in Florida were susceptible to N. viridis, with the exception of Citrus aurantium L., which suggests that there is need for management of this invasive pest in Florida citrus groves. Murraya paniculata L., Hibiscus rosa-sinensis L., and Punica granatum L. were also acceptable hosts for N. viridis. Sexually reproducing female N. viridis produced significantly more eggs than those reproducing asexually. Based on our results, propagation of M. paniculata and other citrus relatives should be discouraged around citrus groves in Florida. Given the fitness benefit of sexual reproduction in this pest, pheromone-based tools like mating disruption and mass trapping of adult males could be considered as part of an integrated pest management program with insecticides.

Intraspecific trait variation and changing life-history strategies explain host community disease risk along a temperature gradient.

Predicting how climate change will affect disease risk is complicated by the fact that changing environmental conditions can affect disease through direct and indirect effects. Species with fast-paced life-history strategies often amplify disease, and changing climate can modify life-history composition of communities thereby altering disease risk. However, individuals within a species can also respond to changing conditions with intraspecific trait variation. To test the effect of temperature, as well as inter- and intraspecifc trait variation on community disease risk, we measured foliar disease and specific leaf area (SLA; a proxy for life-history strategy) on more than 2500 host (plant) individuals in 199 communities across a 1101 m elevational gradient in southeastern Switzerland. There was no direct effect of increasing temperature on disease. Instead, increasing temperature favoured species with higher SLA, fast-paced life-history strategies. This effect was balanced by intraspecific variation in SLA: on average, host individuals expressed lower SLA with increasing temperature, and this effect was stronger among species adapted to warmer temperatures and lower latitudes. These results demonstrate how impacts of changing temperature on disease may depend on how temperature combines and interacts with host community structure while indicating that evolutionary constraints can determine how these effects are manifested under global change. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Contribution of the life‐history traits of a plant pathogen to the development of field epidemics

AbstractThe pathogenicity‐related traits of biotrophic plant pathogens are usually measured on the individual host plant, at the scale of a single pathogen life cycle, whereas epidemic development in the field encompasses a succession of cycles. It remains unclear which traits make the greatest contribution to pathogen fitness in the field and to epidemic severity. The objective of this study was to determine the contributions of elementary pathogenicity traits to epidemic development in field conditions. We challenged a set of wheat cultivars with three different leaf rust isolates, under both controlled and field conditions, in 3 consecutive years. Infection efficiency, latent period, lesion size, spore production per lesion and spore production capacity were measured in the greenhouse, whereas disease severity was measured in the field. Most, but not all, of the pathogenicity traits were related to each other. All traits contributed to epidemic development in the field, but to different extents. Surprisingly, lesion size and spore production per lesion were inversely correlated with epidemic severity. Conversely, there was a strong positive correlation between spore production capacity and pathogen fitness in the field, in accordance with the concept of propagule pressure as a strong determinant of invasion success. Severe epidemics were mostly associated with small lesions with a high spore production capacity, high infection efficiency and a short latent period.

Whitefly-Mediated Transmission and Subsequent Acquisition of Highly Similar and Naturally Occurring Tomato Yellow Leaf Curl Virus Variants.

Begomoviruses are whitefly-transmitted viruses that infect many agricultural crops. Numerous reports exist on individual host plants harboring two or more begomoviruses. Mixed infection allows recombination events to occur among begomoviruses. However, very few studies have examined mixed infection of different isolates/variants/strains of a Begomovirus species in hosts. In this study, the frequency of mixed infection of tomato yellow leaf curl virus (TYLCV) variants in field-grown tomato was evaluated. At least 60% of symptomatic field samples were infected with more than one TYLCV variant. These variants differed by a few nucleotides and amino acids, resembling a quasispecies. Subsequently, in the greenhouse, single and mixed infection of two TYLCV variants (variant #2 and variant #4) that shared 99.5% nucleotide identity and differed by a few amino acids was examined. Plant-virus variant-whitefly interactions including transmission of one and/or two variants, variants' concentrations, competition between variants in inoculated tomato plants, and whitefly acquisition of one and/or two variants were assessed. Whiteflies transmitted both variants to tomato plants at similar frequencies; however, the accumulation of variant #4 was greater than that of variant #2 in tomato plants. Despite differences in variants' accumulation in inoculated tomato plants, whiteflies acquired variant #2 and variant #4 at similar frequencies. Also, whiteflies acquired greater amounts of TYLCV from singly infected plants than from mixed-infected plants. These results demonstrated that even highly similar TYLCV variants could differentially influence component (whitefly-variant-plant) interactions.

Cooperative Behaviors in Group-Living Spider Mites

Cooperative behaviors are evolutionary stable if the direct and/or indirect fitness benefits exceed the costs of helping. Here we discuss cooperation and behaviors akin to cooperation in subsocial group-living species of two genera of herbivorous spider mites (Tetranychidae), i.e., the largely polyphagous Tetranychus spp. and the nest-building Stigmaeopsis spp., which are specialized on grasses, such as bamboo. These spider mites are distributed in patches on various spatial scales, that is, within and among leaves of individual host plants and among individual hosts of single or multiple plant species. Group-living of spider mites is brought about by plant-colonizing foundresses ovipositing at local feeding sites and natal site fidelity, and by multiple individuals aggregating in the same site in response to direct and/or indirect cues, many of which are associated with webbing. In the case of the former, emerging patches are often composed of genetically closely related individuals, while in the case of the latter, local patches may consist of kin of various degrees and/or non-kin and even heterospecific spider mites. We describe and discuss ultimate and proximate aspects of cooperation by spider mites in host plant colonization and exploitation, dispersal, anti-predator behavior, and nesting-associated behaviors and conclude with theoretical and practical considerations of future research on cooperation in these highly rewarding model animals.

The bright side of parasitic plants: what are they good for?

Parasitic plants are mostly viewed as pests. This is caused by several species causing serious damage to agriculture and forestry. There is however much more to parasitic plants than presumed weeds. Many parasitic plans exert even positive effects on natural ecosystems and human society, which we review in this paper. Plant parasitism generally reduces the growth and fitness of the hosts. The network created by a parasitic plant attached to multiple host plant individuals may however trigger transferring systemic signals among these. Parasitic plants have repeatedly been documented to play the role of keystone species in the ecosystems. Harmful effects on community dominants, including invasive species, may facilitate species coexistence and thus increase biodiversity. Many parasitic plants enhance nutrient cycling and provide resources to other organisms like herbivores or pollinators, which contributes to facilitation cascades in the ecosystems. There is also a long tradition of human use of parasitic plants for medicinal and cultural purposes worldwide. Few species provide edible fruits. Several parasitic plants are even cultivated by agriculture/forestry for efficient harvesting of their products. Horticultural use of some parasitic plant species has also been considered. While providing multiple benefits, parasitic plants should always be used with care. In particular, parasitic plant species should not be cultivated outside their native geographical range to avoid the risk of their uncontrolled spread and the resulting damage to ecosystems.

EPIPHYTOTIOLOGY OF PHYTOHELMINTHIASIS IN THE 21st CENTURY

Plant parasitic nematodes are recognized as one of the biggest threats to crop production. Annual crop loss from phytohelminths range from 78 to 128 billion US Dollars. The initial position of the epiphytotic process (EP) theory in phytohelminthiasis is to recognize the infestation as a form of parasitism, and therefore, for the phytohelminth species to be preserved, they need a mandatory and constant change by their pathogen of individual host plants, which is externally perceived as an infection. Such process, i.e. a continuous chain of systematic incidence, occurs involving infected plants (a source of an infectious agent), the mechanism of preserving and transmitting the phytohelminthiasis pathogen, and a susceptible plant(s), which is the biological basis for the epiphytotic process. Based on the analysis of the literature and original data, the primary factors (a source of invasion, a mechanism of preserving and transmitting the pathogen, and a susceptible host plant) and secondary factors (abiotic, biotic, anthropogenic, and social factors) of the epiphytotic process are considered for various phytohelminthiases. From the point of view of epiphytotiology, the list of host plants for the phytohelminthiasis pathogen should include those species of susceptible plants that are naturally included in the epiphytotic process and that provide the indefinitely long existence of the phytohelminth in populations of susceptible plants. The epiphytotic process provides the existence, reproduction and spread of phytohelminths in the nature and agricultural ecosystems.

Whole-Genome Deep Sequencing Reveals Host-Driven in-planta Evolution of Columnea Latent Viroid (CLVd) Quasi-Species Populations.

Columnea latent viroid (CLVd) is one of the most serious tomato diseases. In general, viroids have high mutation rates. This generates a population of variants (so-called quasi-species) that co-exist in their host and exhibit a huge level of genetic diversity. To study the population of CLVd in individual host plants, we used amplicon sequencing using specific CLVd primers linked with a sample-specific index sequence to amplify libraries. An infectious clone of a CLVd isolate Chaipayon-1 was inoculated on different solanaceous host plants. Six replicates of the amplicon sequencing results showed very high reproducibility. On average, we obtained 133,449 CLVd reads per PCR-replicate and 79 to 561 viroid sequence variants, depending on the plant species. We identified 19 major variants (>1.0% mean relative abundance) in which a total of 16 single-nucleotide polymorphisms (SNPs) and two single nucleotide insertions were observed. All major variants contained a combination of 4 to 6 SNPs. Secondary structure prediction clustered all major variants into a tomato/bolo maka group with four loops (I, II, IV and V), and a chili pepper group with four loops (I, III, IV and V) at the terminal right domain, compared to the CLVd Chaipayon-1 which consists of five loops (I, II, III, IV and V).

Congruent population genetic structures and divergence histories in anther-smut fungi and their host plants Silene italica and the Silene nutans species complex.

Study of the congruence of population genetic structure between hosts and pathogens gives important insights into their shared phylogeographical and coevolutionary histories. We studied the population genetic structure of castrating anther-smut fungi (genus Microbotryum) and of their host plants, the Silene nutans species complex, and the morphologically and genetically closely related Silene italica, which can be found in sympatry. Phylogeographical population genetic structure related to persistence in separate glacial refugia has been recently revealed in the S.nutans plant species complex across Western Europe, identifying several distinct lineages. We genotyped 171 associated plant-pathogen pairs of anther-smut fungi and their host plant individuals using microsatellite markers and plant chloroplastic single nucleotide polymorphisms. We found clear differentiation between fungal populations parasitizing S.nutans and S.italica plants. The population genetic structure of fungal strains parasitizing the S.nutans plant species complex mirrored the host plant genetic structure, suggesting that the pathogen was isolated in glacial refugia together with its host and/or that it has specialized on the plant genetic lineages. Using random forest approximate Bayesian computation (ABC-RF), we found that the divergence history of the fungal lineages on S.nutans was congruent with that previously inferred for the host plant and probably occurred with ancient but no recent gene flow. Genome sequences confirmed the genetic structure and the absence of recent gene flow between fungal genetic lineages. Our analyses of individual host-pathogen pairs contribute to a better understanding of co-evolutionary histories between hosts and pathogens in natural ecosystems, in which such studies remain scarce.

Small world in the real world: Long distance dispersal governs epidemic dynamics in agricultural landscapes

Outbreaks of a plant disease in a landscape can be meaningfully modelled using networks with nodes representing individual crop-fields, and edges representing potential infection pathways between them. Their spatial structure, which resembles that of a regular lattice, makes such networks fairly robust against epidemics. Yet, it is well-known how the addition of a few shortcuts can turn robust regular lattices into vulnerable ‘small world’ networks. Although the relevance of this phenomenon has been shown theoretically for networks with nodes corresponding to individual host plants, its real-world implications at a larger scale (i.e. in networks with nodes representing crop fields or other plantations) remain elusive. Focusing on realistic spatial networks connecting olive orchards in Andalusia (Southern Spain), the world’s leading olive producer, we show how even very small probabilities of long distance dispersal of infectious vectors result in a small-world effect that dramatically exacerbates a hypothetical outbreak of a disease targeting olive trees (loosely modelled on known epidemiological information on the bacterium Xylella fastidiosa, an important emerging threat for European agriculture). More specifically, we found that the probability of long distance vector dispersal has a disproportionately larger effect on epidemic dynamics compared to pathogen’s intrinsic infectivity, increasing total infected area by up to one order of magnitude (in the absence of quarantine). Furthermore, even a very small probability of long distance dispersal increased the effort needed to halt a hypothetical outbreak through quarantine by about 50% in respect to scenarios modelling local/short distance pathogen’s dispersal only. This highlights how identifying (and disrupting) long distance dispersal processes may be more efficacious to contain a plant disease epidemic than surveillance and intervention concentrated on local scale transmission processes.

Floral Visitation Can Enhance Fitness of Helicoverpa armigera (Lepidoptera: Noctuidae) Long-Distance Migrants.

Numerous insect species engage in seasonal, trans-latitudinal migration, in response to varying resource availability, climatic conditions and associated opportunities, to maximize fitness and reproductive success. For certain species, the interaction between migrant adults and individual host plants is well-studied under laboratory conditions, but scant knowledge exists on the nutritional ecology of wild (i.e., field-caught) moths. During 2017-2018, we trapped adults of the cotton bollworm Helicoverpa armigera (Hübner) along its migration pathway in northeastern China and used pollen grain analysis to assess its visitation of particular host plants. Next, we assessed life history effects of adult feeding on carbohydrate-rich resources, for migrant individuals. Pollen grain analysis revealed H. armigera visitation of 32 species from 28 families, with the largest carrier ratio for northward migrants. Evening primrose (Oenothera spp.) accounted for 48% of pollen grains, indicating a marked H. armigera feeding preference. Furthermore, feeding on sugar-rich foods benefited adult fitness, enhanced fecundity by 65-82% and increased flight distance by 38-55% as compared to unfed individuals. Also, the degree of enhancement of reproduction and flight performance following sugar feeding varied between different migratory cohorts. Our work combines (polymerase chain reaction [PCR]-assisted) palynology and laboratory-based life history trials to generate novel perspectives on the nutritional ecology of long-distance migratory insects. These findings can aid the development of population monitoring and 'area-wide' management strategies for a globally-important agricultural pest.

The microbiome of the Melitaea cinxia butterfly shows marked variation but is only little explained by the traits of the butterfly or its host plant.

SummaryUnderstanding of the ecological factors that shape intraspecific variation of insect microbiota in natural populations is relatively poor. In Lepidopteran caterpillars, microbiota is assumed to be mainly composed of transient bacterial symbionts acquired from the host plant. We sampled Glanville fritillary (Melitaea cinxia) caterpillars from natural populations to describe their gut microbiome and to identify potential ecological factors that determine its structure. Our results demonstrate high variability of microbiota composition even among caterpillars that shared the same host plant individual and most likely the same genetic background. We observed that the caterpillars harboured microbial classes that varied among individuals and alternated between two distinct communities (one composed of mainly Enterobacteriaceae and another with more variable microbiota community). Even though the general structure of the microbiota was not attributed to the measured ecological factors, we found that phylogenetically similar microbiota showed corresponding responses to the sex and the parasitoid infection of the caterpillar and to those of the host plant's microbial and chemical composition. Our results indicate high among‐individual variability in the microbiota of the M. cinxia caterpillar and contradict previous findings that the host plant is the major driver of the microbiota communities of insect herbivores.

Effect of plant chemical variation and mutualistic ants on the local population genetic structure of an aphid herbivore.

Plants exhibit impressive genetic and chemical diversity, not just between species but also within species, and the importance of plant intraspecific variation for structuring ecological communities is well known. When there is variation at the local population level, this can create a spatially heterogeneous habitat for specialised herbivores potentially leading to non-random distribution of individuals across host plants. Plant variation can affect herbivores directly and indirectly via a third species, resulting in variable herbivore growth rates across different host plants. Herbivores also exhibit within-species variation, with some genotypes better adapted to some plant variants than others. We genotyped aphids collected across 2years from a field site containing ~200 patchily distributed host plants that exhibit high chemical diversity. The distribution of aphid genotypes, their ant mutualists, and other predators was assessed across the plants. We present evidence that the local distribution of aphid (Metopeurum fuscoviride) genotypes across host-plant individuals is associated with variation in the plant volatiles (chemotypes) and non-volatile metabolites (metabotypes) of their host plant tansy (Tanacetum vulgare). Furthermore, these interactions in the field were influenced by plant-host preferences of aphid-mutualist ants. Our results emphasise that plant intraspecific variation can structure ecological communities not only at the species level but also at the genetic level within species and that this effect can be enhanced through indirect interactions with a third species.

Plant geographic origin and phylogeny as potential drivers of community structure in root‐inhabiting fungi

Abstract Root‐inhabiting fungal communities, including mutualists and antagonists, influence host plant performance, and can potentially shape plant community composition. However, there is uncertainty about how root‐inhabiting fungal communities are structured, and if fungal community characteristics are significant predictors of host plant abundance. In this study, we first assessed how root‐inhabiting fungal communities were structured in relation to the phylogeny and geographic origins (native vs. exotic) of their host plants in an old‐field community. In addition, we took into consideration the spatial arrangements (i.e. physical locations) of the individual host plants. We then tested if the relative abundances of pathogenic and beneficial arbuscular mycorrhizal (AM) fungi could predict host plant abundances. We found that host plant phylogeny was an important factor in structuring the whole fungal community, irrespective of host plant origin. Furthermore, the spatial arrangements of individual host plants were a strong predictor of AM fungal community structure. Host plant phylogeny and spatial arrangements appeared to similarly affect the structure of pathogenic fungal communities. No distinct differences were observed between native and exotic plant species in fungal community characteristics. The relative abundances of AM and pathogenic fungi were not significant predictors for observed abundances of their host plants. Synthesis. Host plant phylogeny and spatial arrangements can structure naturally occurring root‐inhabiting fungal communities. The absence of distinct differences in fungal community composition, including pathogens, in exotic and native plants suggests long residence times and the consequent naturalization of exotic species in the region, allowing for the establishment of similar plant–microbial interactions between native and exotic species.

Butterfly–host plant synchrony determines patterns of host use across years and regions

Variation in the degree of synchrony among host plants and herbivores can disrupt or intensify species interactions, alter the strength of natural selection on traits associated with phenological timing, and drive novel host plant associations. We used field observations from three regions during four seasons to examine how timing of the butterfly herbivore Anthocharis cardamines relative to six host plant species (Arabis hirsuta, Cardamine pratensis, Arabis glabra, Arabidopsis thaliana, Thlaspi caerulescens and Capsella bursa‐pastoris) influenced host species use and the choice of host plant individuals within populations. Butterflies laid a larger fraction of their eggs on species that were closer to the butterfly's preferred stage of development than on other host species. Within host plant populations, butterflies showed a stronger preference for individuals with a late phenology when plants within the population were on average more developed at the time of butterfly flight. Our results suggest that changes in synchrony between herbivores and their host plants are associated with changes in both host species use and the choice of host plant individuals differing in phenology within populations. This is likely to be an important mechanism generating variation in interaction intensities and trait selection in the wild, and therefore also relevant for understanding how anthropogenic induced changes, such as global warming, will influence natural communities.

The biotypes and host shifts of cotton-melon aphids Aphis gossypii in northern China

Aphis gossypii is a globally distributed species and therefore has a highly variable life cycle. Populations of A. gossypii in northern China exhibit greater genotypic diversity and a broader host range, yet the details of life cycles of different biotypes is still unclear. In this study, the Cytb and 16S gene regions of A.gossypii collected from 5 common summer hosts and 4 primary hosts were analyzed. A total of 57 haplotypes were obtained from 1 046 individual A.gossypii sequences. The sequence included 44 variable sites, 27 of which were parsimony informative sites and 17 of which were singleton variable sites. The most frequent 3 haplotypes were found in 896 individuals, representing a total of 85.7% of all individuals and 36 haplotypes were found in 1 individual. A neighbor-joining tree was constructed using 21 haplotypes that were found in more than 2 individuals. Considering the individual host plant, 5 biotypes were identified. Type 1 corresponded exactly to the cucurbit host-race and the other 4 biotypes were found as cotton host-races. Type 3 was the most abundant biotype in cotton fields in northern China.

Fungi reduce preference and performance of insect herbivores on challenged plants.

Although insect herbivores and fungal pathogens frequently share the same individual host plant, we lack general insights in how fungal infection affects insect preference and performance. We addressed this question in a meta-analysis of 1,113 case studies gathered from 101 primary papers that compared preference or performance of insect herbivores on control vs. fungus challenged plants. Generally, insects preferred, and performed better on, not challenged plants, regardless of experimental conditions. Insect response to fungus infection significantly differed according to fungus lifestyle, insect feeding guild, and the spatial scale of the interaction (local/distant). Insect performance was reduced on plants challenged by biotrophic pathogens or endophytes but not by necrotrophic pathogens. For both chewing and piercing-sucking insects, performance was reduced on challenged plants when interactions occurred locally but not distantly. In plants challenged by biotrophic pathogens, both preference and performance of herbivores were negatively impacted, whereas infection by necrotrophic pathogens reduced herbivore preference more than performance and endophyte infection reduced only herbivore performance. Our study demonstrates that fungi could be important but hitherto overlooked drivers of plant-herbivore interactions, suggesting both direct and plant-mediated effects of fungi on insect's behavior and development.

Individual host taxa may resist the climate-mediated trend in herbivory: Cenozoic herbivory patterns in western North American oaks

The interactions between plant-eating insects and their hosts are hypothesized to shift dramatically as global temperatures increase. Examination of modern and fossil leaves has led to predictions of increased herbivory in a warmer world. However, climate induced changes in insect feeding may differ between individual host plants and their broader plant community. To examine how climate affects herbivory in a single, ecologically widespread host taxon, we studied insect feeding damage on the fossilized leaves of oaks (Quercus), which are host to a diverse group of herbivores and have been broadly distributed in temperate Northern Hemisphere floras throughout the Cenozoic. We examined oak leaves with ages that range from Eocene to Pliocene (38 to 5Ma) with a range of mean annual temperatures (6.5–17.6°C) and 3-month average precipitation levels (9.8–78.2cm) to test whether insect damage on oaks is more intense in floras that grew under warmer and wetter conditions.Examination of leaves from thirteen floras from the western United States shows that neither mean annual temperature nor average precipitation was a significant determinant of overall insect damage. However, herbivory made by endophagous insects (gallers and leaf miners) was more prevalent in dry conditions. Temperature also was a significant determinant of gall and leaf mine damage; warmer floras tended to have more galls and fewer leaf mines. In addition, gallers and leaf miners show a high degree of host-fidelity through time. This pattern of host-fidelity suggests that feeding of endophagous insect herbivores is more climatically sensitive than that of more generalized, exophagous herbivores, and that future climatic change may not affect all host-herbivore systems, nor all herbivores within a single host system, in the same ways. Therefore, an increase in outbreaks of specialized insects on their hosts may be more likely than broadly increased herbivory as global temperatures increase.

Impacts of lodgepole pine dwarf mistletoe (Arceuthobium americanum) infestation on stand structure and fuel load in lodgepole pine dominated forests in central Colorado

Parasitic plants are capable of causing substantial alterations to plant communities through impacts on individual host plants. Lodgepole pine dwarf mistletoe is an important parasite in forests of the western USA that causes reductions to productivity and is thought to alter wildland fuel complexes. These impacts are hypothesized to vary with infestation severity. To test this, we used a linear mixed modeling approach to evaluate the relationship between dwarf mistletoe infestation severity and parameters representing stand structure and surface and canopy fuels in infested lodgepole pine stands in central Colorado. Infestation severity was negatively related to live basal area, average tree size, canopy base height, canopy fuel load, and canopy bulk density, and was positively related to the loading of woody surfaces fuels greater than 0.64 cm in diameter. No relationship was detected between infestation severity and live tree density, or live crown ratio. These results confirm the long-held assumption that dwarf mistletoe increases surface fuel loading in lodgepole pine communities, but also suggest that infested stands have reduced amounts of available canopy fuel. These findings have implications for potential fire behavior and highlight the importance of dwarf mistletoe in predicting the spatial and temporal dynamics of wildland fuels.

Oviposition site selection of the Alcon blue butterfly at the northern range margin

Female oviposition decisions in insects may strongly affect offspring growth and survival, and thus determine population performance. In this study, we examined oviposition site selection in the xerophilous ecotype of the endangered myrmecophilous butterfly Phengaris (=Maculinea) alcon (Lepidoptera, Lycaenidae) in Estonia, at the northern distribution margin of both the butterfly and its host plant, Gentiana cruciata L. Egg distribution on individual host plants appeared to be highly uneven: plants carrying high egg loads contrasted to a high proportion of host plants without any or with a few eggs. Host plant use for oviposition was strongly dependent on plant characteristics and environmental context. Host plant height relative to the surrounding vegetation rather than the absolute height of host plants was a key factor determining the use of particular host plant individuals for oviposition. In particular, plants protruding above surrounding vegetation had a higher probability of being used for oviposition, and carried more eggs. Additionally, the number of eggs laid on individual host plants was positively associated with the presence of flowers and the number of shoots. More aggregated host plants received fewer eggs than those with less conspecifics around. Feeding damage by wild herbivores, found in a substantial proportion of the butterfly’s host plants, strongly reduced the number of eggs on individual plants. Our results underline the need to assure that butterfly’s host plants do not become overgrown by surrounding vegetation. Best practices for opening vegetation around host plants may need further studies that explicitly account for butterfly’s host ants—their abundance in relation to vegetation height and their response to opening vegetation.