The effect of the mirid bug Capsodes infuscatus on fruit production of the geophyte Asphodelus ramosus in a desert habitat

The effect of feeding of the mirid bug Capsodes infuscatus on fruit production of the geophyte Asphodelus ramosus was studied in a desert area in Israel. Plant and bug densities and percent loss of fruit production were measured in a relatively dry lower colluvial slope, an intermediate upper colluvial slope, and a relatively mesic wadi. Overall damage levels were very high, with 100% loss of fruit production in many plants. Within each habitat, the number of nymphs per plant clone was positively correlated with the number of ramets per clone and percent damage was positively correlated with number of nymphs per clone. However, percent damage was not correlated with number of plants per clone in any habitat. Although damage did significantly increase with plant density in the slope habitats, mean damage to fruit production per clone was lowest (50%) in the wadi where Asphodelus density was highest. As new ramets are tightly interwoven with their mother plants, occupation of new microsites depends on establishment of new clones from seeds. Therefore, the strong and density-dependent reduction in fruit production inflicted by Capsodes on the Asphodelus population on the slope has the potential to regulate the plant density in this habitat.     

Plant‐mediated interactions between two herbivores differentially affect a subsequently arriving third herbivore in populations of wild cabbage

• Plants are part of biodiverse communities and frequently suffer from attack by multiple herbivorous insects. Plant responses to these herbivores are specific for insect feeding guilds: aphids and caterpillars induce different plant phenotypes. Moreover, plants respond differentially to single or dual herbivory, which may cascade into a chain of interactions in terms of resistance to other community members. Whether differential responses to single or dual herbivory have consequences for plant resistance to yet a third herbivore is unknown.
• We assessed the effects of single or dual herbivory by Brevicoryne brassicae aphids and/or Plutella xylostella caterpillars on resistance of plants from three natural populations of wild cabbage to feeding by caterpillars of Mamestra brassicae. We measured plant gene expression and phytohormone concentrations to illustrate mechanisms involved in induced responses.
• Performance of both B. brassicae and P. xylostella was reduced when feeding simultaneously with the other herbivore, compared to feeding alone. Gene expression and phytohormone concentrations in plants exposed to dual herbivory were different from those found in plants exposed to herbivory by either insect alone. Plants previously induced by both P. xylostella and B. brassicae negatively affected growth of the subsequently arriving M. brassicae. Furthermore, induced responses varied between wild cabbage populations.
• Feeding by multiple herbivores differentially activates plant defences, which has plant‐mediated negative consequences for a subsequently arriving herbivore. Plant population‐specific responses suggest that plant populations adapt to the specific communities of insect herbivores. Our study contributes to the understanding of plant defence plasticity in response to multiple insect attacks.

     

Variability in space and time: contrasting fruit distribution patterns in the deceptive orchid Orchis militaris

• In angiosperms, a decrease in fruit production towards the apex of individual inflorescences is usually observed. Orchids are thought to be primarily pollination‐limited species, and non‐uniform pollination could cause this decrease pattern in several species. Fruit production was investigated in relation to flower position and floral display size in Orchis militaris (Orchidaceae), a deceptive species.
• Over 2 years, eight populations of O. militaris were studied and fruit position along the inflorescence was recorded. Generalised linear models were performed to examine the effect of population, year, flower position and floral display size on fruit production.
• The dominant pattern was characterised by a higher fruit set in the middle part of the inflorescence (parabolic pattern). A non‐directional pattern of fruit production was also detected in some populations. Within a given population, patterns were generally consistent among years. In one of the two study years and in one of the eight populations specifically, the proximal‐to‐distal decrease in fruit production was dramatic in plants with a large floral display but weak or absent in small displays.
• Our study demonstrates the intraspecific diversity of fruit distribution patterns in O. militaris. Non‐uniform pollination along the inflorescence is likely to be responsible for the parabolic pattern, while irregular visitation could explain the non‐directional pattern of fruit production. Pattern variation among years and between populations could arise from spatiotemporal variation in pollinator assemblages. Resource competition effects could explain the interaction effect between display size and flower position.

     

The effect of inflorescence display size and flower position on pollination success in two deceptive and one rewarding orchid

• Inflorescence display size and flower position on the inflorescence play important roles in plant reproduction, in the formation of fruits and are primarily linked to pollinator behaviour. We used three orchids to determine how visitation rates and choice of pollinator depend on number and position of the flowers along the inflorescence.
• We measured reproductive success in (1) natural conditions, (2) hand-pollination experiments and (3) an experimental design, by modifying composition of inflorescences in populations of two deceptive orchids, Orchis anthropophora and O. italica, and one rewarding orchid, Anacamptis coriophora subsp. fragrans.
• There were no differences in natural fruit production in relation to flower position on the inflorescence (i.e. upper versus lower part), suggesting no preference of pollinators for different parts of the inflorescence. Hand-pollination experiments highlighted low pollen limitation in A. coriophora subsp. fragrans but high limitation in O. italica and O. anthropophora. Reproductive success of deceptive orchids in experimental plots decreased significantly when flowers on the upper half of the inflorescence were removed leading to reduced floral display, while reproductive success of the nectariferous species did not differ significantly.
• Our data highlight that in the examined orchids there is no clear relationship between fruit formation and flower position along inflorescences. Thus we can affirm that, for orchids, the entire inflorescence plays a dominant role in insect attraction but the part of the flower spike does not influence the choice of the insect. This implies that all flowers have the same possibility of receiving visits from pollinators, and therefore each flower has the same opportunity to set fruit.

     

The influence of herbivory and weather on the vital rates of two closely related cactus species

Herbivory has long been recognized as a significant driver of plant population dynamics, yet its effects along environmental gradients are unclear. Understanding how weather modulates plant–insect interactions can be particularly important for predicting the consequences of exotic insect invasions, and an explicit consideration of weather may help explain why the impact can vary greatly across space and time. We surveyed two native prickly pear cactus species (genus Opuntia) in the Florida panhandle, USA, and their specialist insect herbivores (the invasive South American cactus moth, Cactoblastis cactorum, and three native insect species) for five years across six sites. We used generalized linear mixed models to assess the impact of herbivory and weather on plant relative growth rate (RGR) and sexual reproduction, and we used Fisher's exact test to estimate the impact of herbivory on survival. Weather variables (precipitation and temperature) were consistently significant predictors of vital rate variation for both cactus species, in contrast to the limited and varied impacts of insect herbivory. Weather only significantly influenced the impact of herbivory on Opuntia humifusa fruit production. The relationships of RGR and fruit production with precipitation suggest that precipitation serves as a cue in determining the trade‐off in the allocation of resources to growth or fruit production. The presence of the native bug explained vital rate variation for both cactus species, whereas the invasive moth explained variation only for O. stricta. Despite the inconsistent effect of herbivory across vital rates and cactus species, almost half of O. stricta plants declined in size, and the invasive insect negatively affected RGR and fruit production. Given that fruit production was strongly size‐dependent, this suggests that O. stricta populations at the locations surveyed are transitioning to a size distribution of predominantly smaller sizes and with reduced sexual reproduction potential.     

A biotrophic fungal infection of the great burnet Sanguisorba officinalis indirectly affects caterpillar performance of the endangered scarce large blue butterfly Phengaris teleius

Interactions between ecological communities of herbivores and microbes are commonly mediated by a shared plant. A tripartite interaction between a pathogenic fungus-host plant-herbivorous insect is an example of such mutual influences. In such a system a fungal pathogen commonly has a negative influence on the morphology and biochemistry of the host plant, with consequences for insect herbivore performance. Here we studied whether the biotrophic fbngus Podosphaera ferruginea, attacking the great burnet Sanguisorba officinalis, affects caterpillar performance of the endangered scarce large blue butterfly Phengaris teleius. Our results showed that the pathogenic ftmgus affected the number and size of inflorescences produced by food-plants and, more importantly, had in direct, plant-mediated effects on the abun dance, body mass and immune response of caterpillars. Specifically, we found the relationship between caterpillar abundance and variability in inflorescence size on a plant to be positive among healthy food-plants, and negative among infected food-plants. Caterpillars that fed on healthy food-plants were smaller than those that fed on infected food-plants in one studied season, while there was no such difference in the other season. We observed the relationship between caterpillar immune response and the proportion of infected great burnets within a habitat patch to be positive when caterpillars fed on healthy food-plants, and negative when caterpillars fed on infected food-plants. Our results suggest that this biotrophic fungal infection of the great burnet may impose a significant indirect influence on P. teleius caterpillar performance with potential consequences for the population dynamics and structure of this endangered butterfly.     

Ecological and Evolutionary Interactions between Wild Crucifers and Their Herbivorous Insects

Abstract Insects feeding on ten species of wild crucifer were investigated. Differences in host plant range and insect community structure were examined with regard to anti-herbivore defense mechanisms. Most of the crucifer species deterred insect herbivory by disappearing in the summer or by lowering their intrinsic quality as food for insects. Species with these defense mechanisms were exploited by only a few specialized herbivorous insects that seemed to have counter defenses. The plants without these defense mechanisms were used by many herbivorous insect species. Rorippa indica lacked direct defenses, but supported a low total density of herbivore individuals. This crucifer has an indirect defense mechanism: ants attracted to floral nectar defended the plant from deleterious herbivores. Crucifers that disappeared seasonally lacked other anti-herbivore defense mechanisms. This suggests that the phonological response is an alternative other responses to herbivore attack.     

Effects of non-native <Emphasis Type="Italic">Spartina patens</Emphasis> on plant and sediment organic matter carbon incorporation into the local invertebrate community

The cycling of organic matter through food webs is a fundamental process that may be altered by the invasion of non-indigenous plants. We explored consequences of the invasion of non-indigenous Spartina patens to the composition of soil organic matter (SOM) and to detritivore and herbivore diets in the upper salt marsh within Corrubedo National Park, northwest Spain. We tested for the incorporation of S. patens carbon (C) into SOM and by detritivores and herbivores using stable isotope analysis, focusing primarily on detritivorous enchytraeid oligochaetes and herbivorous insects. Stable isotope results indicated that C derived from S. patens has been incorporated into SOM. Elevated densities of enchytraeids in stands of S. patens, and their incorporation of C derived from this plant, suggested that dense patches of S. patens may facilitate detritivore populations. In contrast, although insect herbivores used S. patens as habitat, there was little isotopic evidence for the widespread incorporation of S. patens-derived C by these consumers. The population and dietary response of enchytraeids to S. patens suggests that S. patens invasion could indirectly influence soil processes and pathways mediated by detritivore activity (e.g., soil respiration rates, nutrient retention and transformation, energy flow). The loss of food resources to insect herbivores alters local food webs. However, insect herbivores may move and feed on native plants elsewhere. As a result, insect populations may be less immediately impacted than soil detritivore populations by S. patens. Our study suggests that the influences of S. patens invasion extend beyond the more obvious changes in native plant abundance, to include differing responses in the cycling of organic matter between detritivore and insect herbivore food web pathways.     

Local and landscape scale drivers of Euschistus servus and Lygus lineolaris in North Carolina small grain agroecosystems

1. Crop production sequences influence arthropod populations in temporally unstable row crop systems. Winter wheat (Triticum aestivum L.) represents one of the earliest abundant crops in south-eastern United States. This study aims to understand primary source habitats driving brown stink bug, Euschistus servus (Say), and tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), population abundance in wheat.
2. To better understand these relationships, adult and nymphal densities were in wheat fields weekly from flowering through harvest in 2019 and 2020. Geospatial data were used to measure landscape composition surrounding sampled fields. We investigated the influence of landscape predictors on E. servus and L. lineolaris abundance using generalized linear mixed modelling.
3. Field size, proportion of agriculture, proportion of wheat area, and proportion of soybean Glycine max L.) area from the previous year in the surrounding landscape were associated with E. servus abundance in wheat. Similarly, L. lineolaris abundance was associated with proportion of wheat area and soybean area from the previous year.
4. These results reveal the influence of soybean area planted the previous year on insect pest densities the following spring in wheat. Further, results suggest agricultural landscapes dominated by wheat are associated with decreased pest abundance across the sampled region.

     

Increased nutrient availability decreases insect resistance in cranberry

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Indirect effects of deer on insect pests and soybean plants

1. White-tailed deer (Odocoileus virginianus Zimmermann) and insect pests negatively affect soybean production; however, little is known about how these herbivores potentially interact to affect soybean yield. Previous studies have shown deer browse on non-crop plants affects insect density and insect-mediated leaf damage, which together reduce plant reproductive output. In soybeans, reproductive output is influenced by direct and indirect interactions of different herbivores.
2. Here, we quantified indirect interactions between two groups of herbivores (mammals and insects) and their effects on soybean growth and yield. We examined responses of insect pest communities along a gradient of deer herbivory (29% to 49% browsed stems) in soybean monocultures.
3. Structural equation models showed that deer browse had direct negative effects on soybean plant height and yield. Deer browse indirectly decreased insect-mediated leaf damage by reducing plant height. Deer browse also indirectly increased pest insect abundance through reductions in plant height. Similarly, deer herbivory had an indirect positive effect on leaf carbon: nitrogen ratios through changes in plant height, thereby decreasing leaf nutrition.
4. These results suggest that pest insect abundance may be greater on soybean plants in areas of higher deer browse, but deer browse may reduce insect herbivory through reduced leaf nutrition.

     

The arthropod predators of ant-mimetic and aposematic prey: a serological analysis

Abstract.

• 1 ELISA (enzyme-linked immunosorbant assay) was used to identify the arthropod predators of two common herbivores of a desert lupine: the aposematic plant bug Lopidea nigridea and the ant-mimetic plant bug Coquillettia insignis.
• 2 Despite the fact that the prey are closely related, the two antisera were sufficiently specific to distinguish between the antigen against which they were formed and the antigen of the other species: both antisera were 3 times as reactive against their homologous antigen as they were against their heterologous antigen.
• 3 In tests on gut contents of field-collected predators, ELISA results were generally consistent with laboratory no-choice data for the five most common arthropod species on lupine: there was a strong correlation between attack rates for each predator-prey pair as measured in the laboratory, and per cent positive reactions in ELISA as measured using field-collected predators. In particular, L.nigridea antiserum was shown to be significantly less reactive against the crab spider Xysticus montanensis when compared to C.insignis antiserum, paralleling results of laboratory no-choice experiments.
• 4 The usefulness of serological analysis as a tool for arthropod trophic link identification is discussed.

     

The role of termites in the decomposition of wood and leaf litter in the Southern Guinea savanna of Nigeria

Summary The number of flowers produced by inflorescences of Yucca whipplei (Agavaceae) consistently exceeds the number of fruits produced by about one order of magnitude. To determine the factors responsible for low fruit set, the relation between pollinator availability, the amount of resources spent on reproduction (as indicated by inflorescence size), and the number of fruits matured was studied during 1978 and 1979 at 18 locations in chaparral, coastal sage scrub, and desert scrub communities of southern California.The following results support the conclusion that pollinators do not usually limit fruit production in Yucca whipplei. Rather, fruit production is limited by the amount of resources available to support developing fruits. (1) Fruit production is positively correlated with inflorescence size both within and between populations. The average size of inflorescence for a population is an excellent predictor of mean fruit production. Furthermore, 54% of the total variance in fruit production of individual plants can be explained by inflorescence size. (2) In contrast, although fruit production within most populations is positively correlated with an index of the number of pollinator visits to an inflorescence, the relative abundance of pollinators for a population is a poor predictor of mean fruit production, and only 9% of the total variance in fruit production can be explained by the visitation index. Furthermore, at four sites studied for two years, there was little change in average inflorescence size or fruit production from 1978 to 1979, despite large differences in relative abundance of pollinators at each of the sites. (3) Based on geographic proximity, and physiographic and vegetational similarities, study sites were grouped into regional clusters. Both inflorescence size and fruit production varied considerably between regions. Of the total variation in fruit production, 27% can be attributed to differences between regions. Most of this variation is the result of regional differences in inflorescence size, which in turn influence fruit production.Why does Yucca whipplei produce such large inflorescences if so few fruits can be supported? Two relevant hypotheses are discussed: (1) the floral display is the result of selection for pollen dissemination at the expense of fruit set; and (2) the floral display is the result of selection for a bet-hedging strategy either to increase the probability of adequate pollination when pollinators are unusually rare, or to allow individuals to support more fruits when resources are unusually abundant.     

Glandular trichomes as an inflorescence defence mechanism against insect herbivores in Iberian columbines

Glandular trichomes play a defensive role against herbivores in the leaves of many plant species. However, their functional role in inflorescences has not been studied, even though theory suggests that tissues with a higher fitness value, such as inflorescences, should be better defended. Using manipulative experiments, we analysed the defensive role of glandular trichomes against herbivorous insects in the inflorescence of Iberian columbines (genus Aquilegia), and its inter-population and inter-taxa variation in relation to herbivore abundance and potential selective pressure. The experiments were conducted in eight populations belonging to four subspecies of two columbines (Aquilegia vulgaris and Aquilegia pyrenaica). For each population, we estimated the density of glandular trichomes in the inflorescences, the abundance of insects stuck in the inflorescences, the abundance of small herbivorous insects, the incidence of damage on flowers and fruits, and the fruit set. The density of glandular trichomes on the inflorescence of A. vulgaris and A. pyrenaica was higher in regions of higher herbivore abundance. We also found that when the plants lose the protection of glandular trichomes, small insects have better access to flowers and fruits, causing more damage and reducing plant fitness. This study concludes that glandular trichomes are part of an adaptive response against phytophagous insect herbivory. The observed variation in herbivore pressure between taxa, likely caused by habitat differentiation, might have played a role in trait differentiation through divergent selection. This result adds evidence to the differentiation of the Iberian columbines through habitat specialization.     

Plant neighbours mediate bird predation effects on arthropod abundance and herbivory

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Proximate effects of maternal oviposition preferences on defence efficacy and larval survival in a diet‐specialised tortoise beetle. Who knows best: mothers or their progeny?

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Apparent competition leaves no detectable imprint on patterns of community composition: observations from a natural experiment

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Large herbivores facilitate an insect herbivore by modifying plant community composition in a temperate grassland

Large herbivores often co‐occur and share plant resources with herbivorous insects in grassland ecosystems; yet, how they interact with each other remains poorly understood. We conducted a series of field experiments to investigate whether and how large domestic herbivores (sheep; Ovis aries) may affect the abundance of a common herbivorous insect (aphid; Hyalopterus pruni) in a temperate grassland of northeast China. Our exclosure experiment showed that 3 years (2010–2012) of sheep grazing had led to 86% higher aphid abundance compared with ungrazed sites. Mechanistically, this facilitative effect was driven by grazing altering the plant community, rather than by changes in food availability and predator abundance for aphids. Sheep significantly altered plant community by reducing the abundance of unpalatable forbs for the aphids. Our small‐scale forb removal experiment revealed an “associational plant defense” by forbs which protect the grass Phragmites australis from being attacked by the aphids. However, selective grazing on forbs by sheep indirectly disrupted such associational plant defense, making P. australis more susceptible to aphids, consequentially increasing the density of aphids. These findings provide a novel mechanistic explanation for the effects of large herbivores on herbivorous insects by linking selective grazing to plant community composition and the responses of insect populations in grassland ecosystems.     

Larval parasitism rate increases in herbivore‐damaged trees: a field experiment with cyclic birch feeding moths

Indirect plant defence mechanisms enhance the effectiveness of natural enemies of herbivores. Herbivore‐induced plant volatiles (HIPVs) attract the parasitoids of insect herbivores as shown both in numerous choice tests conducted under laboratory conditions and in relatively few common‐garden setups in agro‐ecosystems. However, the importance of this indirect defence trait at higher levels of biological organization has yet to be investigated through natural field experiments. Here, we report a field experiment of larval parasitism of two cyclic geometrid defoliators in herbivore‐damaged and fairly intact mountain birch Betula pubescens ssp. czerepanovii under natural conditions. Parasitism rates in larvae of the autumnal (Epirrita autumnata) and winter moth (Operophtera brumata) exposed for 30 h on defoliated trees were more than twice as high as those on control trees. This finding indicates that hymenopteran parasitoids were attracted to previously defoliated trees by some cues from the host plants, HIPVs being the most likely candidates. The third trophic level should thus be considered in natural plant herbivore interactions. Furthermore, parasitoids and food resources are key factors in the population regulation of forest insect pests, and indirect plant defences could be important in their interactions. Our research also emphasizes the quality of control treatments in field experiments, since immediate plant responses easily obscure the results as soon as control trees become infested by herbivorous insects.     

Extranuptial nectaries in flowers: ants increase the reproductive success of the ant‐plant Miconia tococa (Melastomataceae)

• Although the production of extranuptial nectar is a common strategy of indirect defence against herbivores among tropical plants, the presence of extranuptial nectaries in reproductive structures is rare, especially in ant‐plants. This is because the presence of ants in reproductive organs can generate conflicts between the partners, as ants can inhibit the activity of pollinators or even castrate their host plants. Here we evaluate the hypothesis that the ant‐plant Miconia tococa produces nectar in its petals which attracts ants and affects fruit set.
• Floral buds were analysed using anatomical and histochemical techniques. The frequency and behaviour of floral visitors were recorded in field observations. Finally, an ant exclusion experiment was conducted to evaluate the effect of ant presence on fruit production.
• The petals of M. tococa have a secretory epidermis that produces sugary compounds. Nectar production occurred during the floral bud stage and attracted 17 species of non‐obligate ants (i.e. have a facultative association with ant‐plants). Ants foraged only on floral buds, and thus did not affect the activity of pollinators in the neighbouring open flowers. The presence of ants in the inflorescences increased fruit production by 15%.
• To our knowledge, the production of extranuptial nectar in the reproductive structures of a myrmecophyte is very rare, with few records in the literature. Although studies show conflicts between the partners in the ant–plant interaction, ants that forage on M. tococa floral buds protect the plant against floral herbivores without affecting bee pollination.