Aboveground Arthropods Research Articles

Functional invertebrate prey groups reflect dietary responses to phenology and farming activity and pest control services in three sympatric species of aerially foraging insectivorous birds.

Farming activity severely impacts the invertebrate food resources of farmland birds, with direct mortality to populations of above-ground arthropods thorough mechanical damage during crop harvests. In this study we assessed the effects of phenological periods, including the timing of harvest, on the composition and biomass of prey consumed by three species of aerial insectivorous birds. Common Swifts Apus apus, Barn Swallows Hirundo rustica and House Martins Delichon urbica breed sympatrically and most of their diet is obtained from agricultural sources of invertebrate prey, especially from oil-seed rape crops. We categorized invertebrate prey into six functional groups, including oil-seed rape pests; pests of other arable crops; other crop-provisioned taxa; coprophilous taxa; and taxa living in non-crop and mixed crop/non-crop habitats. Seasonality impacted functional groups differently, but the general direction of change (increase/decrease) of all groups was consistent as indexed by prey composition of the three aerial insectivores studied here. After the oil-seed rape crop harvest (mid July), all three species exhibited a dietary shift from oil-seed rape insect pests to other aerial invertebrate prey groups. However, Common Switfts also consumed a relative large quantity of oil-seed rape insect pests in the late summer (August), suggesting that they could reduce pest insect emigration beyond the host plant/crop. Since these aerially foraging insectivorous birds operate in specific conditions and feed on specific pest resources unavailable to foliage/ground foraging avian predators, our results suggest that in some crops like oil-seed rape cultivations, the potential integration of the insectivory of aerial foraging birds into pest management schemes might provide economic benefits. We advise further research into the origin of airborne insects and the role of aerial insectivores as agents of the biological control of crop insect pests, especially the determination of depredation rates and the cascading effects of insectivory on crop damage and yield.

Future rainfall variations reduce abundances of aboveground arthropods in model agroecosystems with different soil types

Climate change scenarios for Central Europe predict less frequent but heavier rainfalls and longer drought periods during the growing season. This is expected to alter arthropods in agroecosystems that are important as biocontrol agents, herbivores or food for predators (e.g. farmland birds). In a lysimeter facility (totally 18 3-m2-plots), we experimentally tested the effects of long-term past vs. prognosticated future rainfall variations (15% increased rainfall per event, 25% more dry days) according to regionalized climate change models from the Intergovernmental Panel on Climate Change (IPCC) on aboveground arthropods in winter wheat (Triticum aestivum L.) cultivated at three different soil types (calcaric phaeozem, calcic chernozem and gleyic phaeozem). Soil types were established 17 years and rainfall treatments one month before arthropod sampling; treatments were fully crossed and replicated three times. Aboveground arthropods were assessed by suction sampling, their mean abundances (± SD) differed between April, May and June with 20 ± 3 m-2, 90 ± 35 m-2 and 289 ± 93 individuals m-2, respectively. Averaged across sampling dates, future rainfall reduced the abundance of spiders (Araneae, -47%), cicadas and leafhoppers (Auchenorrhyncha, -39%), beetles (Coleoptera, -52%), ground beetles (Carabidae, -41%), leaf beetles (Chrysomelidae, -64%), spring tails (Collembola, -58%), flies (Diptera, -73%) and lacewings (Neuroptera, -73%) but increased the abundance of snails (Gastropoda, +69%). Across sampling dates, soil types had no effects on arthropod abundances. Arthropod diversity was neither affected by rainfall nor soil types. Arthropod abundance was positively correlated with weed biomass for almost all taxa; abundance of Hemiptera and of total arthropods was positively correlated with weed density. These detrimental effects of future rainfall varieties on arthropod taxa in wheat fields can potentially alter arthropod-associated agroecosystem services.

Plant diversity impacts decomposition and herbivory via changes in aboveground arthropods.

Loss of plant diversity influences essential ecosystem processes as aboveground productivity, and can have cascading effects on the arthropod communities in adjacent trophic levels. However, few studies have examined how those changes in arthropod communities can have additional impacts on ecosystem processes caused by them (e.g. pollination, bioturbation, predation, decomposition, herbivory). Therefore, including arthropod effects in predictions of the impact of plant diversity loss on such ecosystem processes is an important but little studied piece of information. In a grassland biodiversity experiment, we addressed this gap by assessing aboveground decomposer and herbivore communities and linking their abundance and diversity to rates of decomposition and herbivory. Path analyses showed that increasing plant diversity led to higher abundance and diversity of decomposing arthropods through higher plant biomass. Higher species richness of decomposers, in turn, enhanced decomposition. Similarly, species-rich plant communities hosted a higher abundance and diversity of herbivores through elevated plant biomass and C:N ratio, leading to higher herbivory rates. Integrating trophic interactions into the study of biodiversity effects is required to understand the multiple pathways by which biodiversity affects ecosystem functioning.

Choosing and using diversity indices: insights for ecological applications from the German Biodiversity Exploratories.

Biodiversity, a multidimensional property of natural systems, is difficult to quantify partly because of the multitude of indices proposed for this purpose. Indices aim to describe general properties of communities that allow us to compare different regions, taxa, and trophic levels. Therefore, they are of fundamental importance for environmental monitoring and conservation, although there is no consensus about which indices are more appropriate and informative. We tested several common diversity indices in a range of simple to complex statistical analyses in order to determine whether some were better suited for certain analyses than others. We used data collected around the focal plant Plantago lanceolata on 60 temperate grassland plots embedded in an agricultural landscape to explore relationships between the common diversity indices of species richness (S), Shannon’s diversity (H’), Simpson’s diversity (D1), Simpson’s dominance (D2), Simpson’s evenness (E), and Berger–Parker dominance (BP). We calculated each of these indices for herbaceous plants, arbuscular mycorrhizal fungi, aboveground arthropods, belowground insect larvae, and P. lanceolata molecular and chemical diversity. Including these trait-based measures of diversity allowed us to test whether or not they behaved similarly to the better studied species diversity. We used path analysis to determine whether compound indices detected more relationships between diversities of different organisms and traits than more basic indices. In the path models, more paths were significant when using H’, even though all models except that with E were equally reliable. This demonstrates that while common diversity indices may appear interchangeable in simple analyses, when considering complex interactions, the choice of index can profoundly alter the interpretation of results. Data mining in order to identify the index producing the most significant results should be avoided, but simultaneously considering analyses using multiple indices can provide greater insight into the interactions in a system.

Plant-mediated aboveground-belowground interactions: the spider mite perspective

Research on aboveground-belowground interactions has recently experienced a boost. In spite of the relative prosperity of scientific literature featuring aboveground herbivorous arthropods involved in aboveground-belowground interactions, mites have so far been under-represented. To stimulate work with mites in this area, we summarize existing research on plant-mediated interactions of aboveground herbivorous mites and belowground plant-associated organisms. A literature search revealed 17 studies dealing with plant-inhabiting mites, all of which involve the two-spotted spider mite Tetranychus urticae. We categorize the studies according to the belowground biota associated with the mite's host plants, summarize the observed effects of the belowground organisms on the aboveground mites and discuss possible interaction mechanisms. The paucity of existing studies does not yet allow one to draw general conclusions but it is apparent that these aboveground-belowground interactions are strongly context-dependent and vary among plant species and species of belowground biota. In conclusion, we argue that the wealth of knowledge on the behavior, ecology, physiology, and genetic make-up of T. urticae and its natural enemies, and ability to easily rear and perform experimental studies on this species at various spatial scales and organizational levels, make these plant-inhabiting mites perfectly-suited model organisms for future research on aboveground-belowground interactions.

Field response of aboveground non-target arthropod community to transgenic Bt-Cry1Ab rice plant residues in postharvest seasons

Risk assessments of ecological effects of transgenic rice expressing lepidoptera-Cry proteins from Bacillus thuringiensis (Bt) on non-target arthropods have primarily focused on rice plants during cropping season, whereas few studies have investigated the effects in postharvest periods. Harvested rice fallow fields provide a critical over-wintering habitat for arthropods in the Chinese rice ecosystems, particularly in the southern region of the country. During 2006-08, two independent field trials were conducted in Chongqing, China to investigate the effects of transgenic Cry1Ab rice residues on non-target arthropod communities. In each trial, pitfall traps were used to sample arthropods in field plots planted with one non-Bt variety and two Bt rice lines expressing the Cry1Ab protein. Aboveground arthropods in the trial plots during the postharvest season were abundant, while community densities varied significantly between the two trials. A total of 52,386 individual insects and spiders, representing 93 families, was captured in the two trials. Predominant arthropods sampled were detritivores, which accounted for 91.9% of the total captures. Other arthropods sampled included predators (4.2%), herbivores (3.2%), and parasitoids (0.7%). In general, there were no significant differences among non-Bt and Bt rice plots in all arthropod community-specific parameters for both trials, suggesting no adverse impact of the Bt rice plant residues on the aboveground non-target arthropod communities during the postharvest season. The results of this study provide additional evidence that Bt rice is safe to non-target arthropod communities in the Chinese rice ecosystems.

Community-wide effects of below-ground rhizobia on above-ground arthropods

1. Plants take nutrients for their growth and reproduction from not only soil but also symbiotic microbes in the rhizosphere, and therefore below-ground microbes may indirectly influence the above-ground arthropod community through changes in the quality and quantity of plants. 2. Rhizobia are root-nodulating bacteria that provide NH4+ to legume plants. We examined bottom-up effects of rhizobia on the community properties of the arthropods on host plants, using a root-nodulating soybean strain (R+) and a non-nodulating strain (R−) in a common garden. 3. R+ plants grew larger and produced a greater number of leaves than R− plants. We observed 28 species of herbivores and three taxonomic groups of predators on R+ and R− plants. The herbivorous species were classified into sap feeders (12 species) and chewers (16 species). 4. The species richness of overall herbivores, sap feeders, and chewers on R+ plants was greater than that on R− plants. Rhizobia positively affected the abundance of chewers. 5. The community composition of herbivores was significantly different between R− and R+ plants, although species diversity and evenness did not differ. 6. Rhizobia-induced bottom-up effects were transmitted to the third trophic level. The abundance, taxonomic richness, and diversity of the predators on R+ plants were greater but evenness was lower than those on R− plants. The community composition of predators was not affected by rhizobia. 7. These results indicate that the below-ground microbes initiated bottom-up effects on above-ground herbivores and predators through trophic levels.

Root herbivores and detritivores shape above‐ground multitrophic assemblage through plant‐mediated effects

1. Indirect effects mediated by changes in plant traits are the main mechanism by which above- and below-ground herbivores affect each other and their enemies. Only recently the role of decomposers in the regulation of such plant-based systems has been considered. We hypothesized that: (i) below-ground organisms, both herbivores (negative effect on plants) and detritivores (positive effect on plants), will have a profound effect on the interactions among above-ground arthropods; (ii) floral herbivores will negatively affect other above-ground herbivores associated with the plant; and (iii) not only above- and below-ground herbivores, but also detritivores will affect the production of secondary metabolites, i.e. glucosinolates, in the plants. 2. We manipulated the presence of above-ground herbivores, below-ground herbivores and below-ground detritivores on the Brassicaceae Moricandia moricandioides in the field to disentangle their individual and combined effects on other organism groups. We also investigated their effects on the plant's chemical defence to evaluate potential mechanisms. 3. Our results show that not only above- and below-ground herbivores, but also detritivores affected other herbivores and parasitoids associated with the host plant. Most effects were not additive because their strength changed when other organisms belonging to different functional groups or food web compartments were present. Moreover, below-ground herbivore and detritivore effects on above-ground fauna were related to changes in glucosinolate concentrations and in quantity of resources. 4. This study indicates that multitrophic interactions in plant-based food webs can dramatically change by the action of below-ground organisms. One of the most important and novel results is that detritivores induced changes in plant metabolites, modifying the quality and attractiveness of plants to herbivores and parasitoids under field conditions.

Diversity and seasonal phenology of aboveground arthropods in conventional and transgenic maize crops in Central Spain

One of the major concerns regarding the release of Bt maize is its potential negative impact on non-target organisms present in this crop. In this paper, we compare the temporal phenology and community structure of the aboveground arthropods in commercial Bt maize fields in Central Spain with those of conventional maize crops, with or without an insecticide (imidacloprid) seed treatment, over a period of three years. Spiders, harvestmen, centipedes, ground beetles, rove beetles, carrion beetles, click beetles, earwigs and damsel bugs were captured in pitfall traps every year in sufficient number to provide meaningful phenological data. One predator spider and three omnivorous species of ground beetles have been consistently present in the maize fields: Pardosa occidentalis, Poecilus cupreus, Pseudophonus rufipes and Pseudophonus griseus, respectively. Rove beetles were caught to a lesser extent, with three dominant species: Acrotona aterrima, Philonthus varians and Platystethus nitens. The variability in activity–density patterns of the aboveground fauna was mainly influenced by the year, but no detrimental effects could be attributed to Bt maize. The only exception being the changes detected in rove beetles, although these differences were transitory and varied from year to year. No changes in species richness and diversity indices for spiders and ground beetles resulted from treatments. However, imidacloprid-treated maize caused a reduction in species richness of rove beetles, even though the abundance of the main species was not reduced. Our results suggest that Bt maize could be compatible with natural enemies that are common in maize fields in Spain.

NUTRIENT SUBSIDIES TO BELOWGROUND MICROBES IMPACT ABOVEGROUND FOOD WEB INTERACTIONS

Historically, terrestrial food web theory has been compartmentalized into interactions among aboveground or belowground communities. In this study we took a more synthetic approach to understanding food web interactions by simultaneously examining four trophic levels and investigating how nutrient (nitrogen and carbon) and detrital subsidies impact the ability of the belowground microbial community to alter the abundance of aboveground arthropods (herbivores and predators) associated with the intertidal cord grass Spartina alterniflora. We manipulated carbon, nitrogen, and detrital resources in a field experiment and measured decomposition rate, soil nitrogen pools, plant biomass and quality, herbivore density, and arthropod predator abundance. Because carbon subsidies impact plant growth only indirectly (microbial pathways), whereas nitrogen additions both directly (plant uptake) and indirectly (microbial pathways) impact plant primary productivity, we were able to assess the effect of both belowground soil microbes and nutrient availability on aboveground herbivores and their predators. Herbivore density in the field was suppressed by carbon supplements. Carbon addition altered soil microbial dynamics (net potential ammonification, litter decomposition rate, DON [dissolved organic N] concentration), which limited inorganic soil nitrogen availability and reduced plant size as well as predator abundance. Nitrogen addition enhanced herbivore density by increasing plant size and quality directly by increasing inorganic soil nitrogen pools, and indirectly by enhancing microbial nitrification. Detritus adversely affected aboveground herbivores mainly by promoting predator aggregation. To date, the effects of carbon and nitrogen subsidies on salt marshes have been examined as isolated effects on either the aboveground or the belowground community. Our results emphasize the importance of directly addressing the soil microbial community as a factor that influences aboveground food web structure by affecting plant size and aboveground plant nitrogen.

Comparisons of Aboveground Arthropods in Burned, Mowed and Untreated Sites in Sandplain Grasslands on Nantucket Island

-Arthropod abundance and vegetation composition were studied in four 0.25ha grassland plots on Nantucket Island, Massachusetts. Treatments included burning in April, burning in August and mowing in August, in 1983 and again in 1985. Cover and frequency of plants in 1985 was little changed from pretreatment levels. Arthropods were sampled in July, August and September of 1985. In the April burn plot, numbers of Arachnida were lower and Orthoptera were higher throughout the season than in an untreated reference plot. Other orders showed little consistent change. In the August burn and mow plots, total numbers of arthropods, especially Hymenoptera, Orthoptera, and Lepidoptera, were higher early in the season in 1985 compared to the reference plot. Following treatments in August, most orders declined in abundance compared to the reference plot, with the exception of the Homoptera, which increased.

Experimental Manipulation of Herbivores in Native Tallgrass Prairie: Responses of Aboveground Arthropods

-A factorial field experiment was conducted in native tallgrass prairie of eastern Kansas in which pesticides were applied to reduce numbers of below and/or aboveground arthropods on small plots sited within enclosures containing varying densities of the prairie vole Microtus ochrogaster. The numbers of aboveground sucking phytophagous insects were particularly sensitive to the application of below and aboveground pesticides. Auchenorrhyncha (leafhoppers and planthoppers) increased in number on plots treated belowground with isofenphos and ethoprop, suggesting that these insects may interact competitively with belowground arthropods. Sternorrhyncha (primarily aphids) and chewing phytophagous insects (primarily grasshoppers and beetles) did not respond to the soil pesticide treatment. Application of carbaryl to foliage resulted in a decrease in Auchenorrhyncha and an increase in Sternorryncha but no consistent change in numbers of other aboveground arthropods, which apparently migrated readily among the small (9 m2) experimental plots. Varying mammal density did not result in any significant variation in density of aboveground arthropods, and no significant interactions with mammal density were detected in aboveground arthropod responses to either below or aboveground chemical treatment.