Exclusion Cages Research Articles

Characterization of the natural enemy community attacking cotton aphid in the Bt cotton ecosystem in Northern China.

Planting Bt cotton in China since 1997 has led to important changes in the natural enemy communities occurring in cotton, however their specific effect on suppressing the cotton aphids (being notorious in conventional cotton ecosystem) has not been fully documented yet. We observed strong evidence for top-down control of the aphid population, e.g. the control efficiency of natural enemies on cotton aphid increased significantly in open field cages compared to exclusion cages, accounted for 60.2, 87.2 and 76.7% in 2011, 2012 and 2013 season, respectively. The cotton aphid populations peaked in early June to late July (early and middle growth stages) in open field cotton survey from 2011 to 2013. The population densities of cotton aphids and natural enemies were highest on middle growth stage while lowest densities were recorded on late stage for aphids and on early plant stage for natural enemies. Aphid parasitoids (Trioxys spp., Aphidius gifuensis), coccinellids and spiders were key natural enemies of cotton aphid. Briefly, natural enemies can suppress aphid population increase from early to middle plant growth stages by providing biocontrol services in Chinese Bt cotton.

Effects of fish predation on Posidonia oceanica amphipod assemblages

Amphipod assemblages that inhabit Posidonia oceanica seagrass meadows are potentially relevant trophic resources for ichthyofauna. However, the effects of fish predation on amphipod assemblages in this system have received little attention. To address this gap in knowledge, experimental manipulations of predation intensity (exclu- sion and inclusion cages) were conducted at two sites in a Mediterranean marine protected area, where different lev- els of fish predation were expected to occur. We found that in the absence of predatory fishes (exclusion cages), total amphipod density and biomass were higher than in uncaged areas and partially controlled cages. At the species level, Caprella acanthifera and Iphimedia minuta responded to caging with increased abundance, while in most cases dif- ferent species did not exhibit differences in density or bio- mass between treatments. The presence of one enclosed labrid fish predator (inclusion cages) resulted in a lower density and biomass of Aora spinicornis and a lower bio- mass of Phtisica marina, although total amphipod density

The effect of structurally complex corals and herbivory on the dynamics of Halimeda

The calcareous green alga Halimeda is a key contributor to carbonate sediment production on coral reefs. As herbivores have a direct negative effect on the abundance of Halimeda, protection from herbivory is critical for Halimeda growth. Branching corals such as Acropora are likely to provide refugia for Halimeda from grazers, yet studies are scarce. Here, we investigated the vulnerability of two Halimeda species to herbivory using fish exclusion cages and assessed the contribution of coral structural complexity to seasonal changes in Halimeda biomass and morphometrics. While up to 50 % Halimeda abundance was depleted outside cages due to herbivory and the exclusion of large herbivores resulted in an increase in net growth up to threefold, Halimeda recruitment was positively affected by herbivory, more than two times greater outside cages. However, these responses differed between species and seasons; only one species was affected in winter but not summer. Coral structural complexity facilitated an increase of total algal biomass particularly in summer. At the individual level, thalli growing inside the Acropora canopy were always significantly larger (thallus biomass, volume and height) than those growing in exposed areas. We estimated that the carbonate production of Halimeda was nearly three times greater inside refuges provided by Acropora. Because Halimeda species differ in growth rates and susceptibility to grazing, we predict that the ongoing degradation of the habitat complexity provided by branching corals will alter Halimeda community structure and its contribution to local sediment budgets.

Agricultural landscape simplification reduces natural pest control: A quantitative synthesis

Numerous studies show that landscape simplification reduces abundance and diversity of natural enemies in agroecosystems, but its effect on natural pest control remains poorly quantified. Further, natural enemy impacts on pest populations have usually been estimated for a limited number of taxa and have not considered interactions among predator species. In a quantitative synthesis with data collected from several cropping systems in Europe and North America, we analyzed how the level and within-field spatial stability of natural pest control services was related to the simplification of the surrounding landscape. All studies used aphids as a model species and exclusion cages to measure aphid pest control. Landscape simplification was quantified by the proportion of cultivated land within a 1km radius around each plot. We found a consistent negative effect of landscape simplification on the level of natural pest control, despite interactions among enemies. Average level of pest control was 46% lower in homogeneous landscapes dominated by cultivated land, as compared with more complex landscapes. Landscape simplification did not affect the amount of positive or negative interactions among ground-dwelling and vegetation-dwelling predators, or the within-field stability of pest control. Our synthesis demonstrates that agricultural intensification through landscape simplification has negative effects on the level of natural pest control with important implications for management to maintain and enhance ecosystem services in agricultural landscapes. Specifically, preserving and restoring semi-natural habitats emerges as a fundamental first step to maintain and enhance pest control services provided by predatory arthropods to agriculture.

Temperature influences postdispersal predation of weed seeds

Temperature is a key factor for the living organisms on earth. It influences weed management practices, either directly or indirectly. Field experiments were conducted to determine the effect of temperature on the postdispersal seed predation of four important weed species (Cuscuta compestris, Stellaria media, Taraxacum officinale and Veronica persica) in two lucerne fields in Mashhad and Chenaran, north‐eastern Iran. These two cities have the same climate: temperate and cold alpine but the temperature varies between them. Wire mesh cages were used to determine the relative importance of birds in predation and pitfall traps were used to detect the species and the activity density of invertebrate predators. The results showed that the predation preference of different weed species was significantly different between and within fields. Seed predation fluctuated widely throughout the sampling periods, matching the periodic forage harvest and regrowth cycle of lucerne. Despite the level of seed predation fluctuating, it declined toward the last sampling periods. Using wire mesh exclusion cages showed no significant effect of birds on weed seed predation in both fields. Ants, crickets and carabid beetles were the invertebrate seed predators that were caught in the pitfall traps. There were significant correlations between the mean temperature and predator activity densities and also between the predated seeds and the mean air temperature in both locations. The results of this study indicate the significant effect of temperature on postdispersal weed seed predation. Therefore, with respect to climate change and increasing global warming, it would be possible to focus on postdispersal seed predation in weed management in the future.

Field evaluations of the contribution of predators and the parasitoid, Aphelinus mali, to biological control of woolly apple aphid, Eriosoma lanigerum, in Virginia, USA

A series of experiments in Virginia, USA apple orchards evaluated the temporal effects of natural enemies on Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) colonies on potted and mature apple trees. Exclusion cage studies using potted trees resulted in increasing colony numbers on fully caged trees and declining colony numbers or colony extinction on trees exposed to natural enemies. Closer examination of the fate of individual colonies on potted trees produced a similar result and revealed that syrphids oviposited in colonies within two days of tree deployment. Heringia calcarata (Loew) (Diptera: Syrphidae) was the predominant predator and had a greater and more rapid impact on colonies than did the parasitoid Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae). The fate of cohorts of naturally-occurring E. lanigerum colonies on mature trees was examined over two seasons and confirmed that H. calcarata and A. mali were most strongly associated with colony demise.

Spatio-temporal variability in recruitment pattern of the invasive mussels Xenostrobus securis

Spatio-temporal variability in recruitment pattern of the invasive mussels Xenostrobus securis

The Efficacy of Several Biorational Insecticides to Control Western Flower Thrips in Marigold (2013)

Marigold plants (“Discovery Yellow”) were grown from seed, individually potted, and placed into two large exclusion cages for artificial infestation. Five weeks after planting, plants were infested with thrips by releasing 50 females and 50 males into each cage, five times (18, 21, and 28 October; 4 and 18 November) for a total of 1,000 WFT. On 2 December, all plants were treated with Floramite SC (4 oz/100 gal) to control a mite infestation. On December 6 (week 0), WFT infested marigold plants were divided into groups of six and placed randomly inside 18-inch diameter by 30-inch tall cylinder cages. The cages were made of Lexan polycarbonate sheeting with two 8-inch holes on opposing sides …

English

Abstract Crayfish are abundant and important consumers in aquatic food webs and crayfish invasions have demonstrated strong effects of crayfish on multiple trophic levels. Density may be an important factor determining the role of omnivorous crayfish in benthic communities, especially if density alters the strength of trophic interactions. The effect of crayfish density on a simple benthic food web using ceramic tiles was examined in three treatments (crayfish exclusion cage, cage control (open to crayfish), and exposed ceramic tiles) in mesocosms stocked with 6, 12, or 18 crayfish·m-2. We hypothesized that at low densities crayfish consumption of herbivorous chironomids would increase algal abundance, but at high densities crayfish would reduce both periphyton and invertebrates. In the experiment, periphyton and chironomid abundance increased with declining crayfish biomass on day 30 but not day 15. The magnitude of crayfish effects on day 15 periphyton chlorophyll a abundance increased with crayfish biomass, but crayfish effects on day 30 periphyton chlorophyll a or chironomid biomass did not increase with crayfish biomass. In this experiment there was little evidence for a trophic cascade at low crayfish densities and strong omnivory by crayfish dominated trophic dynamics.

Nutrient enrichment overwhelms top-down control in algal communities around cormorant colonies

Expanding populations of the piscivorous seabird Great Cormorant (Phalacrocorax carbo sinensis) in the Baltic Sea can have both bottom-up and top-down effects on lower trophic levels: nutrient runoff (bottom-up) from colonies increases algal growth, while predation on fish (top-down) can lead to decreased fish populations around colonies, potentially causing a trophic cascade and higher grazing pressure on algae due to higher herbivore abundances. In this study, we determined how these top-down and bottom-up processes interact to affect algal communities by using exclusion cages to manipulate the access of fish and herbivores to algae around both colony and control islands, and measuring algal recruitment and herbivory in these cages. The results showed that algal communities do indeed differ significantly between control and colony sites: Fucus vesiculosus, an important foundation species, had lower recruitment around colony sites. We found evidence of increased herbivory on Fucus around colony sites in one year, which may contribute to lower survival and reproduction, but the effect was not consistent. Instead, we suggest that lower recruitment is likely mainly due to nutrient enrichment which leads to increased competition from ephemeral algae, and thus decreased recruitment and abundance of Fucus around colonies. This was also indicated by higher recruitment of several ephemeral algal species around colonies in herbivore exclusion cages, indicating they do indeed benefit from nutrient runoff from colonies. Increased grazing around colonies was able to counteract this to some extent, but not completely. Overall, cormorants can indeed affect lower trophic levels, especially through local bottom-up processes, leading to shifts in community structure and potentially decreased biodiversity due to impairing conditions for the foundation species F. vesiculosus.

Quantifying insect predation with predator exclusion cages: the role of prey antipredator behavior as a source of bias

AbstractThere are limitations imposed by current methodologies to detect and quantify insect predation. However, there has been relatively little effort to experimentally document the sources of biases associated with the various methodologies. In this study, we examined how predation estimates in the field using predator exclusion cages may be biased when one fails to account for antipredator behavioral responses. To do this, we did the usual comparison of the number of insects missing from plants where predators were allowed access to the number missing from plants where predators were excluded, but also determined how many of the missing insects reacted to predators by dropping from plants and how many were actually preyed upon. Our results provide evidence that estimates of insect mortality in the field are significantly reduced if prey antipredator behavior is taken into account. As it is commonly assumed that prey missing in the field are predated, documenting the incidence of predator‐mediated ‘disappearance’ and capturing insect prey before they escape can provide with a relevant estimate of bias.

Positive interactions expand habitat use and the realized niches of sympatric species.

Niche theory, the oldest, most established community assembly model, predicts that in sympatry, the realized niche will contract due to negative interspecific interactions, but fails to recognize the effects of positive interactions on community assembly. The stress gradient hypothesis predicts that positive interactions expand realized niches in stressful habitats. We tested the predictions of the stress gradient hypothesis in a cobble beach model system across both physical and biological stress gradients. We transplanted seven common littoral species within, adjacent to, and below Spartina alterniflora cordgrass stands in control, cage control, predator exclusion cage, shade, and shaded predator exclusion cage treatments to test the hypothesis that cordgrass expands intertidal organism habitats. On cobble beaches, cordgrass ameliorates physical and predation stresses, expanding the distribution and realized niches of species to habitats in which they cannot live without facilitation, suggesting that niche theory and species distribution models should be amended to accommodate the role of positive interactions in community assembly.

Rice Fields Used as Feeding Habitats for Waterfowl throughout the Growing Season

The role of rice fields as feeding habitats for the two main waterfowl herbivores, Eurasian Coot (Fulica atra) and Mallard (Anas platyrhynchos), in the Ebro Delta, a Mediterranean wetland in northeastern Spain, was investigated. Exclusion cages and tethering experiments were deployed within a rice field at the beginning of the growing season (summer 2010) and before harvest (autumn 2010). In summer, waterfowl abundances were low, but cage experiments detected rice field damage by waterfowl grazing through a significant reduction in plant biomass (although consumption was undetectable using tethers). In autumn, waterfowl abundance increased and tethering experiments detected consumption of rice plants with developed seeds, whereas cage experiments did not show grazing effects. Gut content analyses indicate that Mallards are mainly granivorous, feeding mostly on seeds of spiral ditch grass (Ruppia cirrhosa) and rice (Oryza sativa), while Eurasian Coots are herbivorous, feeding mainly on macrophyte leaves. However, stable isotope analyses and mixing model results showed that in the long term both species seem to acquire most of their dietary needs from rice plants and sago pondweed (Potamogeton pectinatus). Dietary analyses confirm the importance of rice in both species' diets but also suggest that waterfowl may undergo seasonal dietary variations. These are mostly influenced by changes in the availability of food resources in the area rather than by their nutritional quality. This study confirms the ecological importance of rice fields as a complementary feeding habitat for waterfowl during the growing season in Mediterranean areas. It also highlights the importance of including these habitats in wetland management for waterfowl conservation.

Small herbivores suppress algal accumulation on Agatti atoll, Indian Ocean

Despite large herbivorous fish being generally accepted as the main group responsible for preventing algal accumulation on coral reefs, few studies have experimentally examined the relative importance of herbivore size on algal communities. This study used exclusion cages with two different mesh sizes (1 × 1 cm and 6 × 6 cm) to investigate the impact of different-sized herbivores on algal accumulation rates on the shallow ( 8 cm body depth) while allowing smaller fishes to access the plots. In contrast to the conclusions of most previous studies, the exclusion of large herbivores had no significant effect on the accumulation of benthic algae and the amount of algae present within the coarse-mesh cages was relatively consistent throughout the experimental period (around 50 % coverage and 1–2 mm height). The difference in algal accumulation between the fine-mesh and coarse-mesh cages appears to be related to the actions of small individuals from 12 herbivorous fish species (0.17 ind. m−2 and 7.7 g m−2) that were able to enter through the coarse mesh. Although restricted to a single habitat, these results suggest that when present in sufficient densities and diversity, small herbivorous fishes can prevent the accumulation of algal biomass on coral reefs.

Use of insect exclusion cages in soybean creates an altered microclimate and differential crop response

Insect exclusion cages are commonly used in agricultural and ecological studies to examine plant-insect interactions in a field setting while maintaining control over insect populations. However, these insect cages can unintentionally alter the climate inside of the cage and impact plant physiology, growth and yield as well as insect populations. This can subsequently affect interpretations of experimental results obtained from caged experiments. To address this concern, we measured meteorological variables in conjunction with soybean physiology, growth, and yield over a two-year period. In a 2011 field study in southern Wisconsin, we compared photosynthetic rates, leaf area index (LAI), soil environmental conditions, and various components of yield for plants grown inside and outside of an industry standard insect cage (Lumite 32×32 mesh). Inside of cages, several variables were higher (P<0.05) including surface (0–6cm) soil moisture (38%), stomatal conductance (42%), and total plant biomass (30%), while LAI was 20% lower (P<0.001) inside of the cages. During the 2012 growing season, we measured wind speed, wind gusts, solar radiation, air temperature and relative humidity inside of cages compared to open field conditions. We found that wind speed and solar radiation were 89% and 42% lower, respectively, and air temperature, relative humidity and vapor pressure deficit were not significantly affected. There was also a significant (P<0.0001) effect of the time of day on differences in wind speed and radiation between cages and open field plots. Our findings suggest that commonly used insect cages significantly alter the microclimate inside of the cage, and create a radiation regime in which the amount of direct and diffuse radiation received by plants is altered compared to the open field. Plant physiological processes and growth are affected by these environmental changes, adding a confounding factor when comparing caged to open field plants. Because the effects are likely a function of the type of cage, and mesh size and color, we recommend that future studies more thoroughly measure the microclimate for a variety of common cage types used in experiments.

Fall Armyworm (Lepidoptera: Noctuidae) Development, Survivorship, and Damage on Cotton Plants Expressing Insecticidal Plant-Incorporated Protectants.

Cotton, Gossypium hirsutum (L.), plants expressing insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on significant acreage across the southern region of the United States. Fall armyworm, Spodoptera frugiperda (J. E. Smith), can be a significant cotton pest in some years, but this species has not been a primary target of Bt cotton technologies. The objective of this study was to quantify fall armyworm larval survivorship and fruiting form injury on transgenic cotton lines expressing Cry1Ac (Bollgard), Cry1Ac+Cry2Ab (Bollgard II), and Cry1Ac+Cry1F (WideStrike) Bt proteins. Larval survivorship and fruiting form damage of fall armyworm on Bollgard, Bollgard II, WideStrike, and non-Bt (control) cotton lines were evaluated in no-choice field studies. Fall armyworm (third instars) were placed on flower buds (squares), white flowers, and bolls, enclosed within a nylon mesh exclusion cage, and evaluated at selected intervals after infestation. Exposure of fall armyworm larvae to Bollgard cotton lines generally resulted in no significant effects on survivorship compared with larvae exposed to the non-Bt cotton line. Survivorship and plant injury by fall armyworm on Bollgard II cotton lines was variable compared with that on non-Bt cotton lines, and significant differences between treatments were inconsistent. Fall armyworm had significantly lower survivorship and caused less plant injury on WideStrike cotton lines than on non-Bt cotton lines across all plant structures. Development and survivorship of fall armyworm larvae on these cotton lines also were evaluated in no-choice laboratory assays by offering the previously described fruiting forms to third instars. Bollgard II and WideStrike cotton lines significantly reduced fall armyworm development and survivorship compared with those larvae offered non-Bt tissue. These results suggest that differences exist among selected Bt cotton technologies in their performance against fall armyworm.

Effects of simulated overfishing on the succession of benthic algae and invertebrates in an upwelling-influenced coral reef of Pacific Costa Rica

Overfishing and nutrient enrichment are among the major local stressors to coral reefs worldwide, as they can alter the benthic reef community by promoting fast growing algae and bioeroders. The Northern coast of Pacific Costa Rica is strongly influenced by seasonal upwelling events that naturally increase nutrient concentrations between December and March. This study therefore investigated the combined effects of simulated overfishing and naturally increased nutrients on benthic community composition and succession on settlement tiles over a period of 24weeks (October 2013 until March 2014) using exclusion cages deployed in a coral reef in the Gulf of Papagayo. Tile cover of functional groups and development of organic C and N on light-exposed and –shaded tile sites were assessed. Results revealed that the exclusion of fish significantly increased the development of organic C and N and decreased the C/N ratio on light-exposed tiles. Large filamentous algae (>2mm), fleshy macroalgae and the colonial ascidian Didemnum sp. (Savigny 1816) (up to 80% tile coverage) were dominant on both tile sites. A significant peak of filamentous algae growth and associated organic matter C/N ratio occurred on light-exposed tiles throughout all treatments in February when nutrient concentrations were elevated. These results suggest that both herbivore exclusion and natural eutrophication have a strong influence on the benthic reef community composition and its early succession patterns. The presence of Didemnum sp. and turf algae could represent good early warning bioindicators for local overfishing and eutrophication and may therefore be included in management and monitoring strategies.

Indirect effects of predators control herbivore richness and abundance in a benthic eelgrass (Zostera marina) mesograzer community.

Herbivore communities can be sensitive to changes in predator pressure (top-down effects) and resource availability (bottom-up effects) in a wide range of systems. However, it remains unclear whether such top-down and bottom-up effects reflect direct impacts of predators and/or resources on herbivores, or are indirect, reflecting altered interactions among herbivore species. We quantified direct and indirect effects of bottom-up and top-down processes on an eelgrass (Zostera marina) herbivore assemblage. In a field experiment, we factorially manipulated water column nutrients (with Osmocote(™) slow-release fertilizer) and predation pressure (with predator exclusion cages) and measured the effects on herbivore abundance, richness and beta diversity. We examined likely mechanisms of community responses by statistically exploring the response of individual herbivore species to trophic manipulations. Predators increased herbivore richness and total abundance, in both cases through indirect shifts in community composition. Increases in richness occurred through predator suppression of common gammarid amphipod species (Monocorophium acherusicum and Photis brevipes), permitting the inclusion of rarer gammarid species (Aoroides columbiae and Pontogeneia rostrata). Increased total herbivore abundance reflected increased abundance of a caprellid amphipod species (Caprella sp.), concurrent with declines in the abundance of other common species. Furthermore, predators decreased beta diversity by decreasing variability in Caprella sp. abundance among habitat patches. Osmocote(™) fertilization increased nutrient concentrations locally, but nutrients dissipated to background levels within 3m of the fertilizer. Nutrient addition weakly affected the herbivore assemblage, not affecting richness and increasing total abundance by increasing one herbivore species (Caprella sp.). Nutrient addition did not affect beta diversity. We demonstrated that assemblage-level effects of trophic manipulations on community structure are the result of distinct and often indirect responses of herbivore species. These results underscore the importance of understanding herbivore-herbivore interactions in a system commonly subjected to both eutrophication and overfishing.

Temporal Effects on the Incidence and Severity of Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Feeding Injury to Peaches and Apples during the Fruiting Period in Virginia.

Exclusion cages were used to compare the incidence and severity of feeding injury from brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), on 'Redhaven' peaches, 'Golden Delicious' apples, and 'Smoothee Golden' apples at harvest, following sequential periods of exposure to natural H. halys populations during the 2011 and 2012 growing seasons in Virginia. The fruit used in these experiments were in orchards or on trees that were not managed for H. halys. Treatments were sets of 50 fruit that were always caged, never caged, or exposed during one interval during the fruiting period of peaches and apples in the Mid-Atlantic region of the United States. The cages effectively prevented feeding injury from H. halys. Peaches and apples that were never caged showed the highest percentages of injured fruit at harvest. Exposure treatment had a significant effect on the percentage of fruit showing external injury at harvest in both years for apples and in 2012 for peaches, and a significant effect on the percentage of apples and peaches showing internal injury at harvest in both years. There was no consistent effect of each exposure period on peach injury, but apples exposed during the mid- to latter portion of the season tended to show most injury. Across all exposure periods, more internal than external injuries were recorded at harvest from peaches, while apples tended to have equal or very similar numbers of both kinds of injury. The implications of these results to H. halys management in eastern apple orchards are discussed.

Seasonal variation of the productivity and quality of permanent pastures in Adisols of temperate regions

With the aim of evaluating the productivity (dry matter yield) and quality (protein and fiber) of pastures in temperate regions of Chile a long-term monitoring experiment was carried out in a representative farm in these regions. The study was carried during the years 2002 - 2012 in a farm located at Region of Los Rios, Chile. The study area was split into fifteen pasture sites, which were evaluated dry matter production by means of the standardized methodology, which considers the location on each pasture site a grazing exclusion cage. With the information generated during the 11 years of measurements, a trend pattern interpolation was developed by a polynomial regression model using fifth grade and centering the independent variable from the second grade on. Each result was classified according to the ranking provided by the BLUP methodology, comparing the results obtained with the average. The analysis of variance mixed model, determined by the variance components, indicated that 60% of the total variation in dry matter production is attributed to seasonality. Only 2.6% of the variation was attributable to the year while a 0.9% was due to differences between pastures sites, during the eleven years of study, with no significant data (p> 0.05). The seasonal distribution of production, concentrated its performance in spring and highest performing months were November, December, January. The quality measured as protein and fiber content of the pasture, does not present statistical differences between years and only differences were determined by seasonality.