Host Plant Patches Research Articles

The dispersal patterns of a migratory insect are driven by biotic interactions

AbstractAimThe distribution of a species in an area depends on the presence of suitable climatic conditions, suitable biotic interactions and species dispersal capabilities. Studies of species migration usually do not include all these factors due to a lack of detailed ecological information or appropriate methods. Here, we present simulations that consider all those factors for the study of the migratory patterns of Urania boisduvalii by incorporating environmental suitability, biotic interactions with its host plants (Omphalea spp.), and the moth dispersal capacity.LocationCuba.TaxonUrania and Omphalea.MethodsOur approach considers changes in the palatability of plants resulting from foraging by moths, as the novel mechanism driving their dispersal. Here, the state of each cell is determined by climate, dispersal, presence of edible food plants and change in food plant palatability.ResultsUrania dispersal occurs among sites with both edible food plants and suitable climates within the dispersal capacity of the moths. The number of isolated clusters of suitable patches decreased with larger dispersal capacities. All simulations where the palatability recovery is faster than palatability loss, lead to an oscillatory pattern of a local nature, while the other ones lead to a steady occupancy or extirpation of the moth species.Main ConclusionsOur results provide theoretical support for the hypothesis that the palatability of food plants drives the pattern of movement of the moths and predict that the relationship between toxic and non‐toxic periods is critical to determining steady occupancy, oscillatory occupancy or extirpation of the moth from the host plant patches. The conceptual framework we used is directly based on classic literature and the methods we used are implemented as an R package. Therefore, our approach is suited to model, in a practical way, invasive species, emerging diseases or migratory species.

A simple definition of food resources for the highly polyphagous Lygus lineolaris (Hemiptera: Miridae) enables prediction of adult abundance.

Lygus lineolaris (Palisot de Beauvois) is a highly polyphagous herbivore with more than 300 known host plants. The high polyphagy has created logistical challenges for understanding its population dynamics. I hypothesized that the primary food resource of this species can be characterized simply, cutting across the multiple host plant species, and enabling a simpler understanding of its population dynamics. The food resource was defined as the apical buds and meristematic tissue and terminal flowers and young seeds. Adult abundance in a habitat was related to the relative abundance of food in the habitat, abundance on a host plant stem was related to the amount of food resource on the stem, and the rate of emigration was lower from host plant patches with higher amounts of food resources. These results suggest that the population dynamics of L. lineolaris depends less on the identity of the host plants and more on the amount of food resource the various host plant species provide.

History of colonisation and updated distribution of the Monarch butterfly Danaus plexippus (Linnaeus, 1758) and its hostplants in mainland Portugal, Azores and Madeira

The first observations of the Monarch butterfly (Danaus plexippus) in Iberia date from 1886, although breeding records emerged almost a century later: 1960 in Spain, 1980s–1990s in Madeira and Azores, and 2003 in mainland Portugal. We reviewed the history of the colonisation of mainland and insular Portugal by the Monarch butterfly and its hostplants (Gomphocarpus fruticosus, G. physocarpus and Asclepias curassavica). We also compiled available historical and recent occurrence records as a basis for countrywide surveys of the butterfly and hostplants, to update their current distributions in Portugal. Locations for only a few of the older records represented newly rediscovered populations in the field, although recent occurrences were often confirmed. Hostplants were scarce and monarchs absent in northern and central mainland Portugal, but both were quite common in the southwest. In Madeira, hostplants were found in two locations, while monarchs were common and widespread. In the Azores, small hostplant patches were observed on four of seven surveyed islands, whereas monarchs were rare and restricted to two islands. Abandoned/semi-abandoned orange orchards represent the butterfly’s stronghold in Portugal, with the species being increasingly scarce along rivers and road verges where hostplants are declining. Hostplant persistence is unstable, with many patches removed, while others have expanded or colonised new areas. Overall, hostplants appear to be declining, with implications for the persistence of monarch butterflies in the country.

Arbuscular mycorrhizal root colonization depends on the spatial distribution of the host plants

Despite their ubiquity in terrestrial ecosystems, arbuscular mycorrhizal fungi (AMF) experience dispersion constraints and thus depend on the spatial distribution of the plant hosts. Our understanding of fungal-plant interactions with respect to their spatial distributions and implications for the functioning of the symbiosis remain limited. We here manipulated the location of habitat patches of Medicago lupulina in two experiments to explore the responses of AMF root colonization and extraradical hyphae. We tested the specific hypothesis that AMF-plant habitats high in connectance would stimulate root colonization and induce denser functional root colonization (colonization rate of arbuscules plus coils) because of higher propagule availability between nearby host plant patches (experiment 1). In experiment 2, we anticipated similar responses in mixed habitats of different soil fertility, namely phosphorus-fertilized or unfertilized soil, and anticipated a higher density of extraradical hyphae in the soil connecting the habitats with increased functional root colonization. In agreement with our hypothesis, we found the highest total and functional root colonization in unfragmented micro-landscapes, describing landscapes that occur within a spatial scale of a few centimeters with the AMF-plant habitats positioned adjacent to each other. In the second experiment, overdispersed micro-landscapes promoted functional root colonization. This study provides experimental evidence that the spatial distribution of habitats can determine AMF abundance at the microscale.

Use of a Camera Trap to Monitor Male Mating Territories of the Imperiled Callophrys irus (Lycaenidae)

Camera trap technology is now commonly used to monitor rare and cryptic species of animals. In this study, we present the first use of a camera trap to monitor the imperiled frosted elfin (Callophrys irus Godart). We placed camera traps at two male mating territories (hereafter, ‘territory’) in north Florida 25 m apart to determine 1) the efficacy of camera traps for use in determining C. irus occupancy and 2) if camera traps can be used to monitor presence of individuals within territories. We marked 15 C. irus, seven females and eight males using a colored permanent marker to identify individuals in and around two territories. After 28.9 and 30.2 trap hours across six days, only one camera detected C. irus. This camera recorded 125 instances where C. irus continually remained within range of the camera trap. Of these, 31 observations included marked individuals, 41 events contained unmarked individuals, and 53 events contained C. irus that were unable to be verified as marked or not. Individuals remained within view of the camera for an average of 95.2 seconds (± 13.93 SE). Of 15 color-marked C. irus, two were observed via camera trap, two by human observers, and one by both camera and human observer. The mean Euclidean distance of resighted individuals was 110.25m (range: 16.4–207.08 m; number of resights ranged from 1–5). This evidence suggests that cameras are unlikely to capture all C. irus activity at a patch due to their limited field of view. Human observers therefore may be necessary to augment monitoring of host plant patches. However, the utility of camera traps demonstrated here offers a valuable tool in C. irus monitoring.

Alleles in metabolic and oxygen-sensing genes are associated with antagonistic pleiotropic effects on life history traits and population fitness in an ecological model insect.

Genes with opposing effects on fitness at different life stages are the mechanistic basis for evolutionary theories of aging and life history. Examples come from studies of mutations in model organisms, but there is little knowledge of genetic bases of life history tradeoffs in natural populations. Here, we test the hypothesis that alleles affecting oxygen sensing in Glanville fritillary butterflies have opposing effects on larval versus adult fitness-related traits. Intermediate-frequency alleles in Succinate dehydrogenase d, and to a lesser extent Hypoxia inducible factor 1α, are associated in larvae with variation in metabolic rate and activation of the hypoxia inducible factor (HIF) pathway, which affects tracheal development and delivery of oxygen to adult flight muscles. A dominant Sdhd allele is likely to cause antagonistic pleiotropy for fitness through its opposing effects on larval metabolic and growth rate versus adult flight and dispersal, and may have additional effects arising from sensitivity to low-iron host plants. Prior results in Glanville fritillaries indicate that fitness of alleles in Sdhd and another antagonistically pleiotropic metabolic gene, Phosphoglucose isomerase, depend strongly on the size and distribution of host plant patches. Hence, these intermediate-frequency alleles are involved in ecoevolutionary dynamics involving life history tradeoffs.

Multi-year occupancy of the hops blue butterfly (Celastrina humulus): habitat patch colonization and extinction

The hops azure (Celastrina humulus) is a locally-abundant, rare butterfly in Colorado and Montana, that uses wild hops (Humulus lupulus) as a host plant. Because of the patchy distribution of wild hops and current land use changes, the butterfly is a species of conservation concern. The hops azure is abundant along the riparian systems of the U.S. Air Force Academy (Academy) because wild hops is readily available and most land-use impacts have not reached much of the Academy. However, the riparian systems of the Academy are experiencing increased flooding from off-base, hard-surface development, making it harder for riparian vegetation, like wild hops, to thrive. To describe the prevalence and persistence of the hops azure, we conducted multi-year occupancy sampling to understand habitat-patch occupancy changes, such as patch extinction and colonization, and to identify factors that impact detectability. Wind speed, the area of wild hops, and the amount of cloud cover and solar exposure influenced probability of hops azure detection. Patch occupancy and extinction are influenced by the area of wild hops, suggesting that as host plant patch sizes get smaller, patch extinction increases and occupancy decreases. Detectability and occupancy were higher than expected, and the probability of patch extinction and colonization were extremely low. Management efforts to expand wild hops growth within the hops azure’s range, increase continuity of wild hops expanses, and retain the hydrology that supports wild hops should increase the stability of azure populations.

Time‐Traveling Larvae Ensure Survival in Small, Synchronously Fluctuating Populations

The tiny gall midge Contarinia vincetoxici is a long-lived insect, although its active life, as adult–egg–growing larva, is brief. Eggs are laid in young flower buds of a swallow-wort, which then develop into conspicuous galls harboring the developing larvae. Mature larvae fall to the ground where they enter a long dormancy, which may last over a decade. Gall populations were monitored in a large host plant patch system over 12 years. Despite poor colonization rates, low local gall densities, and large synchronous density fluctuations, almost all patches seemed to be continually inhabited due to the large hidden underground pool of time-traveling larvae. This photograph illustrates the article “Time-traveling larvae ensure survival in small, synchronously fluctuating populations” by Christer Solbreck and Olof Widenfalk published in Ecosphere. https://doi.org/10.1002/ecs2.3086.

Oviposition response of the biocontrol agent Rhinocyllus conicus to resource distribution in its invasive host, Carduus nutans

Musk thistle, Carduus nutans, is a major noxious weed throughout its non-native range. The flower head weevil, Rhinocyllus conicus, deemed likely to be a strong candidate for biocontrol based on laboratory tests, has proven variable in its efficacy, suggesting a possible influence of ecological context. To improve our understanding of the dynamics of this system, we examined how R. conicus responds to the spatial distribution of musk thistle individuals. We manipulated the size and density of host plant patches to determine their effect on weevil oviposition. Neither patch size nor plant density significantly affected the number of eggs laid by R. conicus. However, plant characteristics such as flower head size, as well as plant height and number of flower heads per plant, significantly influenced oviposition. Although larger thistle flower heads provide more sites for oviposition, there is also more seed production in these heads. Thus, while R. conicus oviposition is highest in larger flower heads, the surplus of seed offsets the effectiveness of biological control. This observation may in part explain the variable levels of control by this biological control agent and ascertains circumstances when augmentative management procedures may be needed.

The Conservation Status of Two Endangered Mariana Butterflies, Hypolimnas octocula marianensis and Vagrans egistina (Nymphalidae)

The Mariana eight-spot butterfly (Hypolimnas octocula marianensis) and the Mariana wandering butterfly (Vagrans egistina) are endemic to the Mariana Islands and both have recently been listed as federally protected under the U.S. Endangered Species Act. We conducted both targeted surveys and grid transect searches on Guam and targeted surveys across the islands of Saipan, Tinian and Rota to locate native hostplants, eggs, caterpillars and adults of these rare insects. Despite having a relatively common hostplant, V. egistina was not found during this study, even in places it had last been found. Although various life stages of H. o. marianensis were documented, the hostplants of this species were heavily impacted by grazing of introduced ungulates; only in native limestone forest with jagged tower karst topography, did hostplants persist, and the butterfly with them. The reasons for the disappearance of V. egistina are not clear, but do not appear to be related to hostplant availability. Our surveys suggest that control of invasive ungulates on Guam will be the single most effective conservation action for Mariana eight-spot recovery, and is essential to any chance of long-term persistence for the species there. H. o. marianensis has significant, unoccupied, hostplant patches on the three northern islands (Rota, Tinian, and Saipan) which might be considered as sites for future translocation and reintroduction efforts, in order to reduce the risk of extinction.

Disturbance induced dynamics of a tritrophic novel ecosystem.

Novel ecosystems formed by invasive plants provide a good opportunity to get insight into early dynamics and pattern formation of these ecosystems. The invasive black locust as host plant, Bruchophagus robiniae as host-specific seed predator and its parasitoids were the components of the studied tritrophic system. To investigate disturbance-driven dynamics of this system we created seed-vacated host plant patches in a field experiment. We removed all pods from selected patches of black locust resulting in an induced local extinction of seed predators and their parasitoids. We hypothesized that disturbance enhances top-down control by parasitoids; this enhanced top-down control decreases seed predation, facilitating the host plant's spread. We found that disturbance modified only parasitism after controlling with year effect: in vacated patches median parasitism was higher than in control patches. Seed predation exceeded its initial level in vacated patches in the third year after the disturbance, but in the fourth year it dropped again presumably due to the strong top-down control. Our findings also suggested that the seed predator was also affected by the bottom-up control of its host plant's density. We found that in the studied new ecosystem the top-down control was strengthened by the disturbance. Since the host plant of the tritrophic system is an invasive species, partial habitat disturbance of such species may increase the severity of parasitoid top-down control, which may reduce seed predation by the herbivores.

Host-plant patch qualities and presence of a likely competitor species affect the distribution and abundance of a rare British moth, Cucullia lychnitis

Understanding the environmental factors that affect the distribution and abundance of rare and threatened species can help identify priority sites for conservation action such as habitat management. The moth Cucullia lychnitis is identified in UK legislation as a priority species for conservation. Its conspicuous larvae feed on a patchily distributed host plant Verbascum nigrum, but are entirely absent from some host plant patches within the species’ range. Environmental variability among patches was investigated to understand factors affecting (i) patch occupancy by C. lychnitis and (ii) abundance of C. lychnitis, where present. Occupancy of individual V. nigrum plants within occupied patches was also investigated. The likelihood of patch occupancy increased with patch size, and decreased with patch isolation. Abundance of C. lychnitis was negatively correlated with patch isolation and with abundance of the weevil Cionus nigritarsis, which exploits the same host plant and may be a competitor. Within occupied patches, larvae of C. lychnitis were significantly more likely to be found on taller plants with more flower spikes; such plants are typical of established rather than newly-created patches. These results may help to guide efforts to conserve C. lychnitis, highlighting the importance of habitat connectivity and indicating potential management actions to promote features positively associated with larval incidence and abundance.

Individually mark–mass release–resight study elucidates effects of patch characteristics and distance on host patch location by an insect herbivore

1. How organisms locate their hosts is of fundamental importance in a variety of basic and applied ecological fields, including population dynamics, invasive species management and biological control. However, tracking movement of small organisms, such as insects, poses significant logistical challenges.2. Mass‐release and individual–mark–recapture techniques were combined in an individually mark–mass release–resight (IMMRR) approach to track the movement of over 2000 adult insects in an economically important plant–herbivore system. Despite its widespread use for the biological control of the invasive thistle Carduus nutans, the host‐finding behaviour of the thistle head weevil Rhinocyllus conicus has not previously been studied. Insects were released at different distances from a mosaic of artificially created host patches with different areas and number of plants to assess the ecological determinants of patch finding.3. The study was able to characterize the within‐season dispersal abilities and between‐patch movement patterns of R. conicus. Weevils found host plant patches over 900 m away. Large patches, with tall plants, situated close to the nearest release point had the highest first R. conicus resights. Patch area and plant density had no effect on the number of weevils resighted per plant; however, R. conicus individuals were more likely to disperse out of small patches and into large patches.4. By understanding how R. conicus locates host patches of C. nutans, management activities for the control of this invasive thistle can be better informed. A deeper mechanistic understanding of host location will also improve prediction of coupled plant–herbivore spatial dynamics in general.

Temperature, leaf cover density and solar radiation influence the abundance of an oligophagous insect herbivore at the southern edge of its range

Altitudinal gradients strongly affect species distribution through the direct and indirect effects of temperature. While numerous studies have been done in the central parts or at the northern edges of species’ distributions, the patterns found at the southern edges of species’ distributions in the southern part of the temperate zone have received much less attention, especially in forest floor insect herbivores. In a case study of the altitudinal influence on insect–plant interactions in forest ecosystems, we examined the insect herbivore Cheilosia fasciata (Diptera: Syrphidae) and its hostplant ramsons Allium ursinum. We studied the influence of altitude, leaf cover density of the host plant, host plant patch size, solar radiation and forest type on C. fasciata. We investigated 0.5 × 0.5 m quadrats in patches of ramsons over several altitudinal gradients across Slovenia. The abundance of C. fasciata increased with altitude, while this pattern was not observed in ramsons. Temperature negatively affected abundance. The leaf cover density of the host plant influenced insect abundance positively only when leaf densities were low. Solar radiation had a positive effect on abundance. Forest type and host plant patch size were less important. The results are discussed in the context of mechanisms affecting altitudinal distribution and climate change.

Using ecological theory to develop recovery criteria for an endangered butterfly

Using ecological theory to develop recovery criteria for an endangered butterfly

Oviposition site selection of an endangered butterfly at local spatial scales

As pre-hibernating larvae of the marsh fritillary (Euphydryas aurinia) have limited mobility essential resources need to be available at a very local scale. We surveyed larval webs (2011–2013), the host plant devil’s bit scabious (Succisa pratensis) (2012), and derived variables from digital orthophotos and digital elevation models (Normalized Differenced Vegetation Index, accumulated sun hours, slope, aspect) to explain the presence–absence and abundance of larval webs at three different spatial grain sizes (5 × 2.5 m, 10 × 10 m, 25 × 25 m) across seven study sites in northern Jutland, Denmark. Two-component hurdle models indicated that host plant abundance was the only important predictor of presence–absence and abundance of larval webs across the seven sites. The strength of the host plant effect on larval web prevalence increased when enlarging spatial grain size. For presence–absence (and less for abundance), the effect of host plants on larval webs varied across study sites. Using mixed effects models, we additionally analysed presence–absence of larval webs (in 1 × 1 m plots) in relation to detailed host plant measurements (abundance and size), vegetation height, and environmental variables (soil temperature, air temperature and soil moisture) across four of the sites. This showed that larval webs were located in the densest parts of the host plant patches. Given the low mobility of pre-hibernating larvae (<0.5 m), our results suggest that females select dense parts within large patches of host plants as oviposition sites. Future management should concentrate on establishing large patches of the larval host plant.

Disease ecology. Ecological and evolutionary effects of fragmentation on infectious disease dynamics.

Ecological theory predicts that disease incidence increases with increasing density of host networks, yet evolutionary theory suggests that host resistance increases accordingly. To test the combined effects of ecological and evolutionary forces on host-pathogen systems, we analyzed the spatiotemporal dynamics of a plant (Plantago lanceolata)-fungal pathogen (Podosphaera plantaginis)relationship for 12 years in over 4000 host populations. Disease prevalence at the metapopulation level was low, with high annual pathogen extinction rates balanced by frequent (re-)colonizations. Highly connected host populations experienced less pathogen colonization and higher pathogen extinction rates than expected; a laboratory assay confirmed that this phenomenon was caused by higher levels of disease resistance in highly connected host populations.

Impact of host plant connectivity, crop border and patch size on adult Colorado potato beetle retention.

Tagged Colorado potato beetles (CPB), Leptinotarsa decemlineata (Say), were released on potato plants, Solanum tuberosum L., and tracked using a portable harmonic radar system to determine the impact of host plant spatial distribution on the tendency of the pest to remain on the colonized host plant or patch. Results confirmed the long residency time on the host plant and showed that close connection of the plant to neighboring plants hastened dispersal between plants. Tracking walking CPB for over 6 h in small potato plots revealed that all types of mixed borders tested (potato/bare ground, potato/timothy and potato/woodland) acted as a strong barrier and retained beetles within the patch. In another experiment in potato patches surrounded by bare ground borders, tracked walking CPB displayed similar behaviour for up to four days. The distribution of turning angles in the CPB walking paths was not uniform and corresponded to beetles following the edge rows of potato patches in response to the crop border barrier or reversing their direction as they reached the end of a row and therefore a border. Patch size had no or little effect on beetle retention in the patch. The relative distribution of counts of tagged beetles detected among small (16 m2), medium (64 m2) and large size (256 m2) patches of potato four days after initial release remained similar to that of numbers released. Even though mixed crop borders were a strong barrier to walking CPB emigrating from potato patches, the departure rate of beetles over time was high. Results suggest that the effect of mixed borders is largely limited to dispersal by walking and does not apply to beetles leaving host patches by flight. The manipulation of crop borders and patch size seem to have limited potential for the management of CPB emigrating from potato fields.

Preparing the way for sterile insect release: Determination of false codling moth distribution across a landscape mosaic

Sterile insect release (SIR) for control of insect pests focuses on release of sterile individuals within the focal crop. Its success is related to the extent to which pest individuals are concentrated in the crop or spread out across the landscape mosaic. However, little is known of the success of SIR relative to spatial densities of target insect pest populations. This is especially so for the false codling moth (FCM) Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), an indigenous moth to Africa and one of considerable phytosanitary significance. The aim here was to establish densities of the moth across a citrus production landscape in South Africa where the pest is particularly significant. Pheromone-baited delta traps were laid out in transects across a commercially important citrus-producing valley to assess the spatial and temporal distribution of wild males, prior to implementation of a commercial SIR programme. Transects included the focal citrus orchards, while also including a range of natural habitat types and elevation gradients. Male FCM were mostly confined to the citrus orchards, while those outside were close to citrus orchards or in alien alternative host plant patches, with only a few male individuals being caught up to 1.5 km from the nearest orchard. This suggests that the indigenous vegetation is supporting only a low FCM population, while, in contrast, citrus orchards are the main reservoir for FCM populations. These findings emphasize the importance of focussing SIR for FCM within the crop and on other, adjacent alien host plants, and not to dissipate releases into the surrounding and extensive natural vegetation.

An integrative approach to understanding host–parasitoid population dynamics in real landscapes

Many of our advances regarding the spatial ecology of predators and prey have been attributed to research with insect parasitoids and their hosts. Host–parasitoid systems are ideal for spatial-ecological studies because of the small size of the organisms, the often discrete distribution of their resources, and the relative ease with which host mortality from parasitoids can be determined. We outline an integrated approach to studying host–parasitoid interactions in heterogeneous natural landscapes. This approach involves conducting experiments to obtain critically important information on dispersal and boundary behavior of the host and parasitoid, large-scale manipulations of landscape structure to reveal the impacts of landscape change on host–parasitoid interactions and temporal population dynamics, and the development of spatially realistic, behavior-based landscape models. The dividends from such an integrative approach are far reaching, as is illustrated in our research on the prairie planthopper Prokelisia crocea and its egg parasitoid Anagrus columbi that occurs in the tall-grass prairies of North America. Here, we describe the population structure of this system which is based on a long-term survey of planthoppers and parasitoids among host–plant patches. We also outline novel approaches to experimentally quantify and model the movement and boundary behavior of animals in general. The value of this information is revealed in a landscape-level field experiment that was designed to test predictions about how landscape change affects the spatial and temporal population dynamics of the host and parasitoid. Finally, with these empirical data as the foundation, we describe novel simulation models that are spatially realistic and behavior based. Drawing from this integrated approach and case study, we identify key research questions for the future.