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Effects of agricultural intensification on ability of natural enemies to control aphids


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Agricultural intensification through increasing fertilization input and cropland expansion has caused rapid loss of semi-natural habitats and the subsequent loss of natural enemies of agricultural pests. It is however extremely difficult to disentangle the effects of agricultural intensification on arthropod communities at multiple spatial scales. Based on a two-year study of seventeen 1500 m-radius sites, we analyzed the relative importance of nitrogen input and cropland expansion on cereal aphids and their natural enemies. Both the input of nitrogen fertilizer and cropland expansion benefited cereal aphids more than primary parasitoids and leaf-dwelling predators, while suppressing ground-dwelling predators, leading to an disturbance of the interspecific relationship. The responses of natural enemies to cropland expansion were asymmetric and species-specific, with an increase of primary parasitism but a decline of predator/pest ratio with the increasing nitrogen input. As such, agricultural intensification (increasing nitrogen fertilizer and cropland expansion) can destabilize the interspecific relationship and lead to biodiversity loss. To this end, sustainable pest management needs to balance the benefit and cost of agricultural intensification and restore biocontrol service through proliferating the role of natural enemies at multiple scales.
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Effects of agricultural intensification on
ability of natural enemies to control
Zi-Hua Zhao
, Cang Hui
, Da-Han He
& Bai-Lian Li
Department of Entomology, College of Agriculture and Biotechnology, China Agricultura l University. Beijing 100193, P. R. China,
Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, Matieland 7602, South Africa,
Mathematical and Physical Biosciences, African Institute for Mathematical Sciences, Muizenberg 7945, South Africa,
College of
Agronomy, Ningxia University, Yinchuan 750021, China,
Ecological Complexity and Modeling Laboratory, Department of
Botany and Plant Sciences, University of California, Riverside, CA 92521-0124, USA,
USDA-China MOST Joint Research Center
for AgroEcology and Sustainability, University of California, Riverside, CA 92521, USA.
Agricultural intensification through increasing fertilization input and cropland expansion has caused rapid
loss of semi-natural habitats and the subsequent loss of natural enemies of agricultural pests. It is however
extremely difficult to disentangle the effects of agricultural intensification on arthropod communities at
multiple spatial scales. Based on a two-year study of seventeen 1500 m-radius sites, we analyzed the relative
importance of nitrogen input and cropland expansion on cereal aphids and their natural enemies. Both the
input of nitrogen fertilizer and cropland expansion benefited cereal aphids more than primary parasitoids
and leaf-dwelling predators, while suppressing ground-dwelling predators, leading to an disturbance of the
interspecific relationship. The responses of natural enemies to cropland expansion were asymmetric and
species-specific, with an increase of primary parasitism but a decline of predator/pest ratio with the
increasing nitrogen input. As such, agricultural intensification (increasing nitrogen fertilizer and cropland
expansion) can destabilize the interspecific relationship and lead to biodiversity loss. To this end,
sustainable pest management needs to balance the benefit and cost of agricultural intensification and restore
biocontrol service through proliferating the role of natural enemies at multiple scales.
In agroecosystem, arthropods provide important ecosystem services due to their abundance and diversity; such
service can be sustained and even enhanced by conserving semi-natural and natural habitats within agricul-
tural landscapes
. This is because many arthropod species are very mobile and need to cross multiple habitats,
including both crop and semi-natural habitats, for food and refuge
. Indeed, heterogeneous landscapes with a
high proportion of semi-natural habitats can sustain a high diversity of aphid natural enemies including specia-
lists and generalists, a prerequisite for effective biocontrol
. As such, the provision of arthropod ecosystem
service in croplands is sensitive to resource availability in surrounding semi-natural habitats
Agricultural intensification, through increasing fertilization input within fields and cropland expansion at
landscape scales, is considered a key driver of biodiversity loss and the decline of ecosystem services
. To this end,
habitat management which optimizes the effect of agricultural landscape structure on the efficacy of biological
control of agricultural pests has become a new paradigm for sustainable pest management
. At the field scale,
agrochemical inputs can have great impacts on arthropod communities through changing plant nutrition,
resulting in a rapid biodiversity loss in agroecosystems
. Increasing fertilizer input within fields affects insects
differently due to the asymmetric responses of different species to changing host nutrition. Phytophagous insects,
which have a relatively rapid developmental rate in high-nutrition plants, are more sensitive to changes in host
nutrition than their natural enemies
. Changes in plant nitrogen availability could trigger a bottom-up effect on
insect survival and the interaction between insect herbivores and pathogenic fungi
. At the landscape scale,
cropland expansion (increasing the proportion of cropland in agricultural landscapes) has been shown to
negatively affect biocontrol efficacy by disproportionally harming the natural enemies of agricultural pests
The effects of landscape structure on pest populations can vary with spatial scale; that is, habitat management
should be prioritized at a specific spatial scale
. The negative effect of agricultural intensification on biocontrol
often peaks at a specific spatial scale
. As such, habitat management is proven here to be most effective at the
optimal spatial scale while making little contribution at other spatial scales
. Moreover, the response of arthro-
11 November 2014
31 December 2014
26 January 2015
Correspondence and
requests for materials
should be addressed to
Z.-H.Z. (zhzhao@cau.
SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 1
pods to landscape structures could also be scale dependent due to
species-specific dispersal ability. For species with strong dispersal
ability (e.g. flying predators such as hover flies, lady beetles, and
lacewings), habitat management should target large spatial scales,
while improving local habitat quality can enhance the activity of
species with weak dispersal ability (e.g. walking predators such as
spiders and Carabid beetles). For example, the species diversity and
abundance of ground-dwelling arthropods could increase after
planting grass strips every 200 m, supplying alterative food resources
and refuge for these natural enemies
. These grass strips can act as
banker plants which release the natural enemy when pest popula-
tions increase in crop fields and conserve them after harvest
. Some
field experiments have examined the effects of landscape complexity
on predation and parasitism at either the field or landscape scales, but
to date studies have not examined both scales concurrently
Higher levels of ecosystem service provision are sometimes
achieved through interactions of species from different functional
, making assessing the effects of agricultural intensification
rather challenging. Many arthropod species belong to different func-
tional modules in the insect community of wheat fields (e.g. cereal
aphid, predator, and parasitic wasp), forming complicated food
. Therefore, landscape modification differentially benefits
some species over others, complicating the biocontrol of cereal
aphids by their natural enemies
. To date, most research has been
conducted for specific insect modules at one particular scale,
emphasizing the need for experiments at multiple scales and target-
ing multiple functional modules
Here, we conducted a field experiment of collecting cereal aphids
and their natural enemies of different functional modules in
Northwest China to elucidate the effects of agricultural intensifica-
tion at both field and landscape scales. Based on empirical evidence
and existing hypotheses in the literature, we specifically addressed
two research questions: i) whether the effects of agricultural intensi-
fication on population and community structures differ at the field
and landscape scale; ii) the potential mechanism behind the scale
dependence of the effects of agricultural intensification (increasing
fertilizer input and cropland expansion) on agricultural arthropods.
Effect of nitrogen fertilizer.In the experiment, the amount of
nitrogen fertilizer ranged from 115.8 kg/ha to 170.6 kg/ha while
the proportion of cropland ranged from 63.73% to 90.25% (see
supplementary Table S1). In total, we collected 24,672 individuals
including 19,723 cereal aphids, 3,679 primary parasitoids, 843 leaf-
ground predators, and 427 ground-dwelling predators.
All selected species (two species in each functional group) were
significantly affected by the increasing input of nitrogen fertilizer
within the sampled fields (Figure 1, see supplementary Table S2).
Specifically, the increasing input of nitrogen fertilizer led to the
increase of the population densities of cereal aphids, their primary
parasitoids, and leaf-dwelling predators. The correlation coefficient
between population density and nitrogen input ranged from 0.3365
(Syrphus nitens) to 0.8653 (Aphidius gifuensis), showing different
sensitivity to applying nitrogen fertilizer within the field (e.g. a pos-
itive correlation for primary parasitoids, in contrast to a negative
correlation for ground-dwelling predators; Figure 1, see supplement-
ary Table S2). The abundance of cereal aphids increased more rapidly
than their natural enemies in response to the increasing input of
nitrogen fertilizer, followed by the primary parasitoids (Figure 1,
see supplementary Table S2), indicating a weakening effect of bio-
control service from applying nitrogen fertilizer within the field in
Effect of cropland expansion.At the population level, agricultural
intensification (AI) caused by increasing proportion of cropland has
a positive effect on the abundance of cereal aphids at all spatial scales
except when measured at the broadest scale (1500 m; Figure 2, see
supplementary Table S3). The correlation coefficients between the
proportion of cropland and the population densities of the two aphid
species (Sitobion avenae and Schizaphis graminum) peaked at the
scales of 800 m and 200 m, respectively. Furthermore, the
correlation coefficients for primary parasitoids and leaf-dwelling
predators were positive, which peaked at the scales of 200 m and
500 m. In contrast, the correlation coefficients became negative for
ground-dwelling predators (see supplementary Table S3). Overall, at
broad scales increasing proportion of cropland had a positive effect
on cereal aphids, leaf-dwelling predators and primary parasitoids but
had a negative effect on ground-dwelling predators (Figure 2, see
supplementary Table S3). Moreover, the response of cereal aphids
and their natural enemies to cropland expansion was species specific.
The parasitic wasps were more sensitive than cereal aphids to
cropland expansion across multiple scales, while even species
within the same module (e.g. the two leaf-dwelling predators, H.
variegata and S. nitens) responded differently (Figure 2, see
supplementary Table S3).
Impact on biocontrol and diversity.At the community level, the
increasing input of nitrogen fertilizer significantly enhanced the
primary parasitism in wheat field (F
56.31, P50.013,
Figure 3A) but negatively affected the predator/pest ratio (Leaf-
dwelling predator: F
54.29, P50.041; Ground-dwelling
predator: F
58.11, P50.005, Figure 3B, C). The increasing
input of nitrogen fertilizer was also detrimental to the species
diversity of natural enemies in the wheat field (F
57.72, P5
0.006, Figure 3D).
Moreover, we selected the scale of 500 m to examine the effects of
the proportion of cropland on predation and parasitism, showing an
insignificant effect on primary parasitism (F
52.36, P50.127,
Figure 4A) but a negative effect on the predator/pest ratio (Leaf-
dwelling predators: F
55.58, P50.020; Ground-dwelling pre-
dators: F
56.97, P50.010, Figure 4B, C) and a negative effect on
the species diversity of natural enemies (F
56.61, P50.012,
Figure 4D).
Differential responses to agricultural intensification.Our results
show that the input of nitrogen fertilizer facilitates the cereal aphid
populations. Surprisingly, increasing nitrogen input did not suppress
the activity of parasitic wasps; rather, it slightly increased the
parasitism of cereal aphids, contrasting the result from Lohaus
et al. (2013) that the parasitism of cereal aphids showed no
difference between conventional and organic wheat fields
However, the density of cereal aphids still increased with the input
of nitrogen fertilizer due perhaps to the rapid development of cereal
aphids in high-nitrogen wheat fields
. As such, cereal aphids were
not controlled by the high parasitism driven by the high nitrogen
input. Other possible reasons include that species at the higher
trophic level (hyperparasitoids) may also gain benefits from
nitrogen input and pose a top-down interference to the interaction
between cereal aphids and their primary parasitoids
. These
results suggest that several modules (parasitoids, leaf- and ground-
dwelling predators) can have strong complementary effects on the
biological control of cereal aphids in wheat fields
Landscape simplification (i.e. a high percentage of arable lands in
agricultural landscapes or homogeneous landscape structure) can
have a negative effect on biological control of cereal aphids
Here, the correlation between the percentage of arable lands in the
agricultural landscape and parasitism decreased as the spatial scale
increases, suggesting that parasitic wasps might respond to changes
in landscape structure at small spatial scales
. Additionally, agricul-
tural intensification can facilitate the population growth of cereal
aphids due to the abrupt decline of natural enemy/pest ratio
. The
SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 2
abundance of ground-dwelling predators decreased significantly
with increasing proportion of cropland at all spatial scales, suggesting
that a homogenous landscape cannot stabilize the population density
of natural enemies due to the importance of semi-natural habitats to
the recruitment of natural enemies
. Therefore, agricultural
intensification, including increasing fertilizer input within fields
and cropland expansion at the landscape scale, can disturb the inter-
specific relationship of arthropod community in wheat fields, which
may have a negative effect on biocontrol of cereal aphids.
Strong evidence shows that species within a same functional mod-
ule can respond differently to changes in landscape structure
. For
example, ladybirds and parasitic wasps differ greatly in their dis-
persal ability and thus respond differently to changes in landscape
composition across spatial scales
. Wheat crop is attacked by mul-
tiple pest species which are then attacked by multiple natural enemies
that perceive/use the mosaic landscape differently at different spatial
. Based on our results, the spatial range for analyzing the effect
of landscape structures on insect communities varied depending on
the particular functional groups
Potential mechanism of differential responses.In agroecosystems,
agricultural intensification is the most important driver for changing
the land cover and soil structure
. In particular, nitrogen deposition
in China’s agroecosystem has increased by about 60% in the past
three decades
, causing great disturbance to the food web of
arthropods. On the one hand, although increasing nitrogen
fertilizers has directly proliferated crop nutrition and yield, it also
accelerates the development rate of herbivorous insects and their
natural enemies to a different extent, with the outbreak of pests
causing serious damage to crops. Two hypotheses have been
proposed so far to explain the effect of increasing nitrogen
fertilizer input on insect performance, namely the plant vigor
hypothesis and nitrogen limitation hypothesis
. These hypotheses
argue that the nitrogen content in plants is an important limiting
factor which dictates the developmental rate, breeding, behavior, and
fecundity of insect herbivores. Contrast to their natural enemies,
these insect pests could benefit more from increasing nitrogen
fertilizer input due to the direct improvement of both food
quantity and quality.
On the other hand, cropland expansion further provides more
resources and habitats for insect pests (resource concentration hypo-
thesis), while the decline of semi-natural habitats from the expansion
eliminates alternative preys and refuges of natural enemies
Moreover, landscape simplification could cause the rearrangement
of habitat patches and reallocation of plant resources. These changes
could further affect the population dispersion and host searching.
The asymmetric responses of cereal aphids and their natural enemies
to cropland expansion could therefore cause the shifts observed in
community structure, leading to biocontrol loss under agricultural
Conclusion.Global environmental changes have been occurring at
multiple spatial scales and are an important driver of changes in
biodiversity composition and population dynamics. Increasing
nitrogen input can facilitate the population of parasitic wasps
while suppressing the activity of ground-dwelling predators
, all
greatly effecting the community structure of natural enemies
within fields. Cropland expansion in agricultural landscapes can
Figure 1
The effects of input of nitrogen fertilizer on cereal aphids and their natural enemies in wheat fields ((A) cereal aphids: solid circular indicates
Sitobion avenae
(Fabricius), hollow circular indictes
Schizaphis graminum
(Rondani); (B) parasitic wasps: solid circular indicates
Aphidius avenae
Haliday, hollow circular indicates
Aphidius gifuensis
Ashmaed; (C) leaf-ground predators: solid circular indicates
Hippodamia variegata
hollow circular indicates
Syrphus nitens
Zetterstedt; (D) ground-dwelling predators: solid circular indicates
Pardosa astrigena
L. Koch hollow circular
Chlaeniu spallipes
SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 3
also shift the natural enemy community, causing the loss of
biocontrol service and the outbreak of cereal aphids at landscape
scale. Therefore, agricultural intensification at both the field and
landscape scales can disturb the food web structure of arthropods
and destabilize the interaction between cereal aphids and their
natural enemies
. Habitat management for sustainable pest
management should be conducted at multiple spatial scales
including the field and landscape scales
The marked changes of different species modules in response to
agricultural intensification suggest that studies on isolated modules
could be misleading, and that quantitative food web metrics need to
be considered in future research
. Future studies should compare
functional groups or interspecific relationship of all species in land-
scapes with different levels of complexity in patch arrangement and
spatial structure in order to distinguish between the intraguild effects
of different biocontrol agents working at different spatial scales
The study area.This experiment was conducted near the city of Yinchuan, Ningxia
Hui Autonomous Region of Northwest China. This agricultural region (Yinchuan
plateau, 1100–1200 m a.s.l) has a temperate continental climate and a long history of
crop culture. The area has an average 3,000 h p.a. of sunshine and an annual mean
temperature of 13.1uC. The type of soil is Chernozem, a typical type of the region. The
area has experienced drastic land use changes from natural habitats to arable land,
forming a gradient of landscape simplification through agricultural intensification in
the past decades. The landscape mosaic consists of different habitat patches including
crops, fallow land, grasslands, and woodlands. Agricultural management within crop
fields has led to a gradual change of soil chemical composistion through frequent use
of nitrogen fertilizer for sustaining high crop yields. These changes could have
affected the distribution and composition of arthropod communities in wheat fields
at both local and regional scales.
Seventeen agricultural sites (see supplementary Table S1) were selected along a
gradient of landscape simplification in a radius of 1500 m among sites, from intensive
agricultural sites with a high percentage of arable land (maximum value 583.26%) to
sites with a low percentage of arable land (minimum value 555.82%). Semi-natural
habitats in these sites, including woodlands and fallow land, remained unchanged
during the experiment period from 2010 to 2011
. The nearest neighbor distances of
these sites ranges from 3000 m to 5600 m.
The experimental region had an old planting history (.30 years) of wheat crop.
Three wheat fields in the center of 1500 m radius were selected in each site. To
simplify the experiment design, we chose the wheat fields with the same wheat variety
and soil type. This has been shown to be an appropriate method for studying the effect
Figure 2
Effect of spatial scales on the Pearson correlation between the
proportion of cropland and the abundance of cereal aphids and their
natural enemy in agricultural landscapes (cereal aphids (individuals/100
straws): solid circular indicates
S. avenae
, hollow circular indicates
; primary parasitoids (individuals/100 straws): solid triangle
A. avenae
, hollow triangle indicates
A. gifuensis
predators (individuals/100 nets): solid square indicates
H. variegata
, hollow
square indictes
S. nitens
; ground-dwelling predators (individuals/traps):
solid rhomb indicates
P. astrigena
, hollow rhomb indicates
C. spallipes
Figure 3
The effects of nitrogen fertilizer input on parasitism, predator/pest ratio, and species diversity in wheat fields ((A) primary parasitism; (B)
predator/pest ratio for leaf-ground predators; (C) predator/pest ratio for ground-dwelling predators; (D) species diversity).
SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 4
of landscape structure on arthropod communities
. Wheat density was kept to
about 400–450 plants per m
, and the irrigation was kept nearly the same across all
studied wheat fields, each year from March to June.
Insect sampling.Two dominant pests, Sitobion avenae (Fabricius) and Schizaphis
graminum (Rondani), and their primary parasitoids, leaf- and ground-dwelling
predators were investigated in the field experiment. As the primary parasitoids spend
their whole larval stage in the mummies of cereal aphids, they can be investigated at
the same time. In each field, five randomly-selected points were used to sample cereal
aphids and their primary parasitoids by visual inspection and hand collection
each point, 100 wheat tillers were selected for investigation (5 minutes for cereal aphid
and 15 minutes for primary parasitoids). All fields were sampled within a two-day
period (for diminishing potential stochasticity); three times per year (14
, and 24
of May -when the population of cereal aphids peaks). All cereal
aphids and their natural enemies were collected before pesticide application (30
July) to ignore the effect of pesticides on the experiment. All aphid mummies
were taken back to the laboratory and reared in the gelatin capsules for 30 days. The
hatched adults of primary parasitoids were collected and conserved in 90% ethyl
The ground-dwelling predators (e.g. Carabid beetles and spiders) are important
natural enemies of aphids
. We used pitfall traps for collecting ground-dwelling
predators at the same five randomly-selected points. In each pitfall trap (6.5 cm in
diameter and 11 cm high), 60 mL mixture of vinegar, sugar, propylene glycol and
water at a ratio of 25151520 were filled in a 0.2-L plastic cup. An odorless detergent
(0.3%) was added into the trap to break the surface tension of the mixture. Ground-
dwelling predators were collected 3 times from 10
to 25
of May in each year. In
every time, the trap was open for five days. Population density of ground-dwelling
predators was calculated in individuals per 5 traps.
The same five randomly-selected points were also used to collect leaf-dwelling
predators (coccinellids, syrphids and lacewings); we used a sweep net (200 meshes)
for this purpose at the same period of pitfall trapping
. We sampled 10 times (nets)
per point by sweeping and thus 50 times (nets) per wheat field. The leaf-dwelling
predators collected in the sweeping were transferred into finger shaped bottles, with
80% ethyl alcohol added into each bottle to preserve the samples. Population density
of leaf-dwelling predators was calculated in individuals per 10 nets. All adult primary
parasitoids, ground- and leaf-dwelling predators were identified to species according
to their morphological and taxonomic characteristics.
Field and landscape survey.Within each field scale, landowners were surveyed by
questionnaires and data was collected regarding type of the fertilizer, insecticide, and
yield. These three variables were obtained through two questions: 1) What is the
amount of fertilizer applied per hectare and its composition? 2) What is the average
yield in sampled wheat fields? Because nitrogen fertilizer is the main limiting resource
for wheat growing and breeding, we calculated the amount of nitrogen fertilizer
applied based on the answers to question 1.
At the landscape scale, geostatistic methods were used for collecting information
on agricultural intensification. Specifically, the spatial arrangement of habitat com-
position in each landscape was derived from the Cropland Data Layer, with a 30-m
resolution, obtained from the Chinese Academy of Sciences. All landscape metrics
were computed using the Patch Analyst extension of FRAGSTATS (ArcGIS 9.3,
2008). For further analysis, proportion of cropland (PC) was indicated by the per-
centage of arable lands in the selected site:
PC%~AREAarable habit at
AREAtotal area
where AREA
arable habitat
and AREA
total area
are the area sizes of arable habitats and
total area in each landscape. The PC was obtained at six spatial scales from 200 to
1500 m based on the buffer circle method in agricultural landscape.
Statistical analysis.The abundance (Individuals per 5 traps for ground-dwelling
predators; per 10 sweeps for leaf-dwelling predators; per 100 wheat tillers for primary
parasitoids) were estimated for further analyses. At the population level, two
dominant species (primary parasitoids: Aphidius avenae and Aphidius gifuensis; leaf-
dwelling predators: Hippodamia variegata and Syrphus nitens; ground-dwelling
predators: Pardosa astrigena and Chlaeniu spallipes) were selected for the analysis in
each module containing natural enemies. To prevent the interference of temporal
trends in the analysis, we detrended population density by regressing population
density against year before calculating standard deviation of detrended population
. The detrended data was used for examining the relationship between
agricultural intensification and insect communities at the six spatial scales. At the
community level, Simpson’s diversity (D~1{Pi(Ni=N)2) was used to calculate
species diversity of natural enemies according to population density.
At the field scale the Pearson correlation was used to examine the relationship
between fertilizer input and the abundance of cereal aphids and their natural enemies.
As the amount of nitrogen fertilizer is strongly correlated with grain yield (covar-
iance), it was removed from the analysis. At the landscape scale, the Pearson cor-
relation was also used to examine the relationship between proportion of cropland
(PC) and the abundance of cereal aphids and their natural enemies at multiple spatial
To analyze the joint effects of nitrogen input within the field and the proportion of
cropland at the landscape level on the distribution of cereal aphids and their natural
Figure 4
The effects of the proportion of cropland at the 500 m scale on parasitism, predator/pest ratio, and species diversity in wheat fields ((A)
primary parasitism; (B) predator/pest ratio for leaf-ground predators; (C) predator/pest ratio for ground-dwelling predators; (D) species diversity).
SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 5
enemies, we applied a linear mixed-effect model (LMM) with the restricted maximum
likelihood method
. Species were lumped together into three modules (aphids,
predators and parasitoids) for calculating the predator/prey ratio and primary
parasitism in wheat fields. Nitrogen fertilizer input and the proportion of cropland
were considered as fixed factors, and the landscape site and year as random factors.
Wald tests were used to examine the significant level of fixed effects and twofold
interactions between them. A backward stepwise procedure was used to examine the
contribution of fixed factors and interactions; the fixed factors with P ,0.05 were left
in the full model. Response factors were log-transformed to meet the Gaussian dis-
tribution requirement. Furthermore, the polynomial effects of landscape structure
were tested by adding the fixed factors, (nitrogen input)
and (the proportion of
, to the model. As none of these factors had noticeable additional explan-
atory power, we considered the relationships between landscape structure and log-
transformed insect population density to be linear. R was used for conducting the
statistical analysis (lme4, packages, R Development Core Team 2005). Sigma Plot 12.5
was used for drawing the graphs.
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We are grateful to Ying Wang, Jia Hang, Ting-Ting Zhang, Ying-shu Zhao, Xiao hu Li, Chun
Lu for field assistance and to Beverley Laniewski for English editing. Financial sup port came
SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 6
from the State Key Program of National Natural Science of China (No. 31400349). CH is
supported by the National Research Foundation of South Africa (grants 76912, 81825 and
89967). BL is partially supported by the University of California Agricultural Experiment
Author contributions
Z.Z. and D.H. designed and conducted the field experiments. Z.Z. conducted the data
analysis. Z.Z., H.C. and B.L. wrote the main manuscript text. All authors reviewed the
Additional information
Supplementary information accompanies this paper at
Competing financial interests: The authors declare no competing financial interests.
How to cite this article: Zhao, Z.-H., Hui, C., He, D.-H. & Li, B.-L. Effects of agricultural
intensification on ability of natural enemies to control aphids. Sci. Rep. 5, 8024;
DOI:10.1038/srep08024 (2015).
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SCIENTIFIC REPORTS | 5 : 8024 | DOI: 10.1038/srep08024 7
... The lethal and sublethal effects of pesticides on individuals and populations may lead to modifications of the structure of the arthropod community. Pesticide use by disrupting top-down control in an agroecosystem may promote secondary pest outbreaks (Guedes et al., 2017;Guedes et al., 2016;Lu et al., 2012;Zhao et al., 2015Zhao et al., , 2017. This might be due to altered community dynamics as seen in the case of imidacloprid application that modulated competition among aphid species to induce a shift in both aphid and natural enemy species dominance (Mohammed et al., 2019). ...
... Phytophagous insects that feed on well-nourished host plants exhibit higher growth rates, higher efficiency of food use, higher fecundity, and higher abundance (Awmack and Leather, 2002;Chen et al., 2010Chen et al., , 2004Karowe and Martin, 1989;Mattson, 1980;Moon and Stiling, 2000;Weibull, 1987;Zhao et al., 2015). An increase in nitrogen input may therefore improve the nutritional quantity (enhanced size of host) or quality of the host supporting the immature developing parasitoid and/or synovigenic species that require host feeding (i.e., feeding on host body fluids) for egg development, such effects of N may thus increase levels of parasitism (e.g., Chen et al., 2010;Gharekhani et al., 2020;Moon and Stiling, 2000;Pekas and W€ ackers, 2020;Sarfraz et al., 2009). ...
... Agricultural landscape simplification through cropland expansion can also increase parasitoid abundance and parasitism rates (Hawro et al., 2017;Zhao et al., 2015), although effects vary according to the ecology or life-history of different species or functional groups. Where host density responds positively to crop monocultures due to a concentration of plant resources (e.g., aphid pests of cereals) there may be a corresponding density-dependent primary parasitoid response in a tri-trophic interaction (Gagic et al., 2012;Hawro et al., 2017). ...
... Since the tender fruits of okra are taken after a little cooking, there is every possibility of retaining toxic residue in food stuff (Amjad et al., 2020). Frequent use of synthetic pesticides indiscriminately leads into disturbance in delicate balance between insect-pests and their natural enemies and enhance resistance to insecticides in the pests (Cothran et al., 2013, Anonymous, 2013, Zhao et al., 2015. To combat with challenges arising from the chemical dependent farming, organic farming is gaining popularity during last decades (Tscharntke et al., 2012, Lobley et al., 2005, Dangour et al., 2010, Willer and Lernoud, 2019. ...
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A field experiment on the yield loss assessment in Okra due to insect-pest was carried out at the research farm of Uttar Banga Krishi Viswavidyalaya, Pundibari, Cooch Behar, West Bengal, India during pre-kharif (15th February‒14th May), kharif (15th May‒14th August)and post-kharif (15th August‒14th November)seasons in 2 years, 2015 and 2016. The experiment was laid out in Randomized Block Design and replicated 6 times. The treatments were T1 (protected by chemical insecticide), T2(protected by organic insecticide), T3(unprotected). The chemical protection significantly suppressed the jassid and % damage by fruit borer in contrast to organic protection and unprotected in all the 3 seasons. However,the ‘t’ test analysis revealed non-significant relation between yield of organically and chemically managed plots and significant relation was found between the yield of untreated with organically and chemically managed plotswhich is directly related with the abundance of insect population.From chemically management 30.52%, 25.16% and 33.26% and from organically managed plots 29.37%, 20.68% and 32.38% gain in yield was recorded in pre-kharif, kharif and post-kharif seasons , respectively. The avoidable losses from chemically protected plots were 23.39%, 20.00% and 24.88% in 3 seasons , respectively. The same from organically managed plots were 22.73%, 16.98% and 24.39% in 3 cropping seasons respectively as mention above. Since, non-significant different in losses of yield lies between chemically and organically protected plots, organic management for pest management may be opted considering all aspects like health, environment and export earnings.
... Since cereal aphid populations can be controlled by beneficial organisms, their impact is highly affected by environmental conditions [236][237][238][239]. For instance, nitrogen fertilizer led to an increase of parasitism of A. colemani and A. rhopalosiphi on S. avenae and R. padi, respectively [239]. ...
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Here, we review the current knowledge on the taxonomy, biodiversity, and ecology of cereal aphid parasitoids in Europe, which include 26 cereal aphid primary parasitoids and 28 hyperparasitoids. We present approaches to studying aphid–parasitoid–hyperparasitoid food webs, as well as the secondary endosymbionts in cereal aphids that may influence parasitoid community composition via their effects on food webs. We also review the effects of agricultural practices, environmental variation, and landscape complexity, on cereal aphid food webs and biological control.
... 5,6 There are numerous species in the family Aphidiidae (Hymenoptera) that have coevolved with and act as parasitoids on aphids (Hemiptera, Aphidoidea), and they constitute a vital natural biocontrol resource against aphid infestations as they form large populations in natural farmland ecosystems. [7][8][9] Biological control may provide a range of benefits to land managers; however, it is important to be aware of the costs and risks and that biocontrol measures may have unintended consequences. 10 Identifying parasitoid species and determining parasitism rates early are key to improving the efficacy of using natural enemies (such as Aphidiinae) in biocontrol, avoiding risks, and eliminating unintended negative consequences in the field. ...
Background: Sitobion miscanthi is a major wheat pest at the grain-filling stage found in China. Identifying parasitoid species and understanding parasitism rates are keys to controlling the aphids via natural enemies in the wheat field. Results: In the present study, a method based on DNA barcoding for early determination of the community composition of Aphidiinae parasitoids and parasitism on the aphid was developed. The proposed method detected Aphidius gifuensis as the predominant parasite with parasitism rates of 40.1 ± 2.8% in 2019, and 65.7 ± 3.7% in 2022, and found that the rate varied significantly among different wheat varieties. COI primers efficiently amplified the Aphidiinae parasitoids COI fragments, moreover amplified the aphid COI fragments derived from parasitized (mummified) S. miscanthi. Thus, the COI barcode is not sufficiently specific to unambiguously detect immature parasitoids inside their S. miscanthi hosts. However, it can be used to detect the DNA extracted from mummified aphids. In contrast, the 16S and LWRh primers effectively amplified and identified the parasitoids in parasitized aphid. The 16S primer was reliable even in the early stages of parasitism(24h), and for DNA samples stored at -20 °C for 5 days. The three barcodes from COI, 16S, and LWRh genes could not clearly distinguish a few certain Aphidiinae species owing to relatively low intraspecific and interspecific diversity. Conclusion: The morphological features remain indispensable when identifying Aphidiinae species. Nonetheless, the COI and 16S primers could be used in combination for monitoring the parasitism rates on S. miscanthi in wheat fields. This article is protected by copyright. All rights reserved.
... At the field scale, an increase in nitrogenous fertilizers changes plant nutrition which might be beneficial for the phytophagous pests, while they are detrimental to natural enemies (Awmack and Leather 2002). Zhao et al. (2015) studied the relative importance of nitrogen input and cropland expansion on cereal aphids and their natural enemies, and they found that this intensification benefited cereal aphids more than primary parasitoids and leaf-dwelling predators, leading to disturbance of the interspecific relationships. More intensive agriculture frequently reduces the availability of non-crop habitats which could be a source of alternate hosts for the natural enemies (Langer and Hance 2004). ...
Biodiversity contributes to ecosystem stability, which provides essential life support and is the basis of adaptation and evolution. India with its rich biodiversity is one of the top ten megadiverse countries in the world. The sustainability of biodiversity is the need of the hour and a matter of concern to ecologists and biologists. The year 2020 was declared the ‘International Year of Plant Health’ (IYPH) by the United Nations to create awareness regarding plant health and the impact of healthy plants and forests on food security, poverty, economic development, and sustainability. The focus for IYPH was to raise global awareness of protecting plant health and protecting the environment. It is documented that annually, up to 40% of global food crops are lost to plant pests and diseases leading to annual agricultural trade losses of over $220 billion, which drastically affects poor rural communities. Insects being the largest group of animals and closely associated with man’s welfare in different forms like pests, natural enemies, producers of economic products, and pollinators are one of the most crucial components of biodiversity. Climate change cannot be blamed for all our pest and disease-related problems as human activities are largely responsible for altering ecosystems, reducing biodiversity, and creating conditions where pests can thrive. When intensive agricultural practices, viz. increased chemical insecticide and fertilizer applications, tillage and irrigation, and heavy mechanization, are followed to cater to the needs of the rapidly increasing human population, the result is a rapid decline in the biodiversity of beneficial insects including natural enemies and pollinators. Studies have clearly indicated that food can be produced in a sustainable manner by conserving biodiversity, the diversity of natural enemies can strengthen biological control of insect pests and the diversity of pollinators can enhance crop yields. Thus, one of the major focuses should be to conserve the beneficial insects, and at this juncture, there is a clear realization that taxonomists, conservationists, and biocontrol workers have a major role to play during IYPH 2020 and beyond. Keywords: Agriculturally important insects, Biological control, Conservation, Insect diversity, Parasitoids, Pollinators, Predators
... This landscape transformation was also identified by Zabel et al. (2019) and Garrett et al. (2018) as a consequence of agriculture intensification. Landscape homogenization has negative impacts on biodiversity loss (Buhk et al. 2017), habitats loss (Nowakowski et al. 2018) and ES degradation (Zhao et al. 2015;Pereira 2020). Landscape heterogeneity was high in scenario A1, where croplands are mixed with woodland and forest and grasslands. ...
Agricultural systems supply a wide range of ecosystem services. Projecting future agricultural land-use changes is key to anticipating the potential impacts of human activities. In this work, we assessed future agricultural land-use changes, using the Dinamica-EGO platform, under three scenarios: A0-(business-as-usual), A1-(sustainable agriculture), and A2-(agricultural intensification) for 2040 in the Šiauliai region (Lithuania). Spatial autocorrelation was evaluated by using a Moran’s I index and the spatial patterns with the Getis analysis and landscape metrics. The results showed that croplands will increase 29.6% in the A0, 14.95% in the A1, and 29.63% in the A3 scenario. According to the Getis results, cold spots are in the surrounding of Šiauliai city, and hot spots in the northeast of the Šiauliai region. It was verified a high cropland fragmentation in A1 and low fragmentation in A0 and A2 scenarios. These results are critical for land management to understand cropland impacts under different scenarios.
... In field crops as brassica and wheat, insecticidal application is mostly obliged by the unavailability of natural enemies to minimize aphids' populations. Sometimes, its populations are poorly managed by natural enemies due to their late arrival and/or early dispersal (Zhao et al. 2015). Late appearance to an aphid-infested area may reflect the prey density, preference, or delayed detection; however, early departure may signify deterrence due to some reason or fear of prey scarcity. ...
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Background Attraction and oviposition preference of the green lacewing, Chrysoperla carnea (Steph.) ( Neuroptera: Chrysopidae), in response to prey availability in an ovipositional site was studied. The study aimed to investigate whether an adult attraction of C. carnea to oviposition on the substrate was affected by aphid juice (AJ) of fresh brassica aphid, Brevicoryne brassica. Result In laboratory bioassay, the number of eggs laid by female was significantly higher on AJ-treated area of substrate than control, indicating that oviposition was influenced by the AJ application. Attraction period of AJ lasted for 4 days. In Y-maze olfactometer studies, video tracking software ANY-maze® indicated that C. carnea spent significant more time in the novel arm provided with AJ, showing an attraction. In the greenhouse study, AJ spray attracted a significantly higher number of male and female and considerably increased the number of eggs laid on brassica plant. Conclusion Fresh AJ may be a potential attractant for raising population of this predatory species at a particular location without being involved in rearing and augmentation process. This finding is of special interest and may be of benefit in biological control. As it is likely that the AJ spray could be used to enhance C. carnea population attraction to the desire field.
... Spatial covariates (SC) in our regression meta-models were time-invariant landscape characteristics that may have influenced pest peaks. Crop proportion was the main driver for pest in our models, and led to a clear positive response of pest insects to increasing cover of a suitable crop (Tscharntke et al. 2007, Avelino et al. 2012, Rand et al. 2014, Zhao et al. 2015, Ricci et al. 2019. Crop proportion at local scale or at global scale led to different peak patterns. ...
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Landscape heterogeneity affects population dynamics, which determine species persistence, diversity and interactions. These relationships can be accurately represented by advanced spatially‐explicit models (SEMs) allowing for high levels of detail and precision. However, such approaches are characterised by high computational complexity, high amount of data and memory requirements and spatio‐temporal outputs may be difficult to analyse. A possibility to deal with this complexity is to aggregate outputs over time or space, but then interesting information may be masked and lost, such as local spatio‐temporal relationships or patterns. An alternative solution is given by meta‐models and meta‐analysis, where simplified mathematical relationships are used to structure and summarise the complex transformations from inputs to outputs. Here, we propose an original approach to analyse SEM outputs. By developing a meta‐modelling approach based on spatio‐temporal point processes (STPPs), we characterise spatio‐temporal population dynamics and landscape heterogeneity relationships in agricultural contexts. A landscape generator and a spatially‐explicit population model simulate hierarchically the pest–predator dynamics of codling moth and ground beetles in apple orchards over heterogeneous agricultural landscapes. Spatio‐temporally explicit outputs are simplified to marked point patterns of key events, such as local proliferation or introduction events. Then, we construct and estimate regression equations for multi‐type STPPs composed of event occurrence intensity and magnitudes. Results provide local insights into spatio‐temporal dynamics of pest–predator systems. We are able to differentiate the contributions of different driver categories (i.e. spatio‐temporal, spatial, population dynamics). We highlight changes in the effects on occurrence intensity and magnitude when considering drivers at global or local scale. This approach leads to novel findings in agroecology where, for example, we show that the organisation of cultivated patches and semi‐natural elements play different roles for pest regulation depending on the scale considered. It aids to formulate guidelines for biological control strategies at global and local scale.
The challenge to reconcile agricultural production with the conservation of biodiversity and associated ecosystems services has triggered interest in the design of pest suppressive landscapes. However, the uniqueness of species-specific responses to management and landscape context hamper our ability to make generalizations for landscape design, and we often lack quantitative indicators to make inferences about the pest suppressive potential of landscape designs. Here I examine the literature to underpin design principles based on source-sink theory. The potential of landscapes to support herbivore populations is associated with the area of source habitat, source strength, and the ability of herbivores to detect host plants. The potential of natural enemies to suppress herbivore populations is associated with their potential for numerical response, time to colonization and natural enemy diversity. Insecticide applications and other intensive management practices can turn treated fields into sinks. The analysis reveals that landscape features or management practices influence multiple processes at the same time, and that well-documented landscape features associated with high pest suppression potential generally discourage herbivores and/or favour natural enemies. The evaluation of landscapes in terms of source habitats for specific herbivores and their natural enemies may reveal context-specific information that allow a better quantitative understanding of pest suppression potential of landscapes.
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Ongoing environmental change affects pest populations, migration, and propensity to damage crops, but the responses to climatic drivers could vary among newly invasive and already naturalized closely related species. To compare these responses of a newly invasive aphid, Metopolophium festucae cerealium (Stroyan), with its naturalized congeneric [M. dirhodum (Walker)] and confamilial [Sitobian avenae (Fab.)], we conducted annual surveys over four years across a total of 141 winter wheat fields in the inland Pacific Northwest, USA. Key climatic factors (cumulative precipitation for each calendar year to sampling date, cumulative degree days), landscape factors (proportion of wheat and landscape diversity within the sample year), and Julian day were calculated for each sampling event, and aphid abundance by species, total aphid abundance, overall species richness, diversity, and aphid community composition were assessed. Metopolophium f. cerealium, the second most abundant species, was positively associated with precipitation, suggesting a projected increase in precipitation in winter and spring in the region could favor its establishment and expansion. Although M. dirhodum and S. avenae linearly (positively) associated with temperature, M. f. cerealium did not, indicating that continued warming may be detrimental to the species. Despite the weak impacts of landscape factors, our study indicated that more wheat generally facilitates cereal aphid abundance. Metopolophium f. cerealium abundance tended to be higher in earlier (May/early June vs. late June/July) samples when wheat crop could be vulnerable to aphid feeding. This study suggests that the new presence of M. f. cerealium has important pest management implications in the region.
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Biodiversity is rapidly declining1, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes4 across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades.
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This study examined the effects of various levels of nitrogen inputs (optimal, insufficient and excessive) and water inputs (optimal, low drought and high drought) to tomato plants (Solanum lycopersicum) on survival and development of an invasive tomato leafminer, Tuta absoluta (Meytick) (Lepidoptera: Gelechiidae). Plant growth i.e. plant height and the number of nodes declined under insufficient or excessive nitrogen treatment. Compared to optimal N, insufficient N treatment decreased leaf N content and increased the carbon/nitrogen ratio (C/N) whereas an excess of N had no effect on both leaf N content and leaf C/N ratio. Sub-optimal nitrogen supplies, water treatments and their interactions, significantly reduced the leafminer survival rate and slowed down its development. Together with the findings from three recent companion studies, we assumed that a combination of changes in nutritional value and chemical defense could explain these observed effects. Furthermore, our findings supported both the "Plant vigor hypothesis" and the "Nitrogen limitation hypothesis".
The spatial structure of agricultural landscapes can have a strong impact on the distribution and diversity of insects. Here we studied the effects of within-field position (edge or center) as well as adjacent habitats on the community structure of the natural enemies of cereal aphids. Twelve agricultural sites were included in the study, with two spring wheat fields selected for each site (one adjacent to an alfalfa field, the other adjacent to a corn field). We sampled two rows per field (1 and 20 m from the edge) using pitfall trapping for ground-dwelling predators, sweep netting for leaf-dwelling predators and hand collecting of aphid mummies for parasitoids. Adjacent alfalfa areas, as opposed to corn fields, can significantly increase the abundance and diversity of leaf-dwelling predators and parasitoids near the field edges. Abundance and diversity were found significantly higher near the edges than in the centers of fields adjacent to alfalfa areas. In contrast, no significant differences were found between edges and centers of fields adjacent to corn fields. Of the fifteen most abundant species, Aphidius avenae (Hali-day), A. gifuensis (Ashmead), Hippodamia variegata (Goeze) and Chrysopa sinica (Tjeder) were significantly more abundant near the edge than in the center. Being adjacent to alfalfa habitats could enhance parasitism and predator/prey ratios of leaf-dwelling predators at the edges, but has no effects on ground-dwelling predators. In conclusion, the effect of within-field position and adjacent habitats on natural enemies of agricultural pests was species specific. This should be considered for designing efficient plans of biological control.
Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning. Although biodiversity is now known to affect ecosystem productivity, its effects on stability are debated. Here we present a long-term experimental field test of the diversity–stability hypothesis. During a decade of data collection in an experiment that directly controlled the number of perennial prairie species, growing-season climate varied considerably, causing year-to-year variation in abundances of plant species and in ecosystem productivity. We found that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production. In particular, the decadal temporal stability of the ecosystem, whether measured with intervals of two, five or ten years, was significantly greater at higher plant diversity and tended to increase as plots matured. Ecosystem stability was also positively dependent on root mass, which is a measure of perenniating biomass. Temporal stability of the ecosystem increased with diversity, despite a lower temporal stability of individual species, because of both portfolio (statistical averaging) and overyielding effects. However, we found no evidence of a covariance effect. Our results indicate that the reliable, efficient and sustainable supply of some foods (for example, livestock fodder), biofuels and ecosystem services can be enhanced by the use of biodiversity.
Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning. Although biodiversity is now known to affect ecosystem productivity, its effects on stability are debated. Here we present a long-term experimental field test of the diversity–stability hypothesis. During a decade of data collection in an experiment that directly controlled the number of perennial prairie species, growing-season climate varied considerably, causing year-to-year variation in abundances of plant species and in ecosystem productivity. We found that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production. In particular, the decadal temporal stability of the ecosystem, whether measured with intervals of two, five or ten years, was significantly greater at higher plant diversity and tended to increase as plots matured. Ecosystem stability was also positively dependent on root mass, which is a measure of perenniating biomass. Temporal stability of the ecosystem increased with diversity, despite a lower temporal stability of individual species, because of both portfolio (statistical averaging) and overyielding effects. However, we found no evidence of a covariance effect. Our results indicate that the reliable, efficient and sustainable supply of some foods (for example, livestock fodder), biofuels and ecosystem services can be enhanced by the use of biodiversity.
Land-cover plays an important role in keeping ecological balance, and research on the landscape pattern of land-cover is of great ecological significance. In this paper, fractal model and other landscape calculation models are applied to analyze the characteristics of land-cover by integrating traditional calculation programs into GIS. In the case study of Zaduo County and Zhiduo County (both located in Qinghai Province), land-cover data of 2000 year and 2007 year are used. The fractal dimension index is obtained by constructing fractal model. Meanwhile, the other indicators of the landscape pattern are calculated through Fragstats software. Based on the indicators, each landscape pattern of the two counties can be ranked according to the complexity (the Fractal Dimension Index-D) level and stability (Stability Index-Si) level, and the landscape pattern characteristics and the evolvement mechanism of the study areas are analyzed. By analyzing landscape pattern characteristics and the evolvement mechanism, the results obtained are extremely useful for the government to optimize landscape pattern and manage land utilization in a sustainable way.
Pitfall traps are widely used for investigating ground‐dwelling arthropods, but have been heavily criticized due to their species‐, habitat‐ and attractant‐specific trapping radius which produces unreliable estimation of species diversity and density.We developed a two‐circle method (TCM) for simultaneously estimating densities of ground‐dwelling arthropods and the effective trapping radius. Multiple pairs of traps are located different distances apart, and the intersection of trapping areas can be calculated using the inverse trigonometric function. The density and effective trapping radius can be estimated from a nonlinear regression of the change in the total number of individuals caught with the distance between the paired pitfall traps.We compared the performance of TCM with the estimator based on the nested‐cross array (NCA) for arranging pitfall traps, by comparing predicted densities from these two methods with the real density obtained from the suction sampling method (SSM).Simulations with known arthropod densities and effective trapping radius suggested that TCM produced accurate density estimation, while NCA significantly underestimated the known density. Pitfall trapping of ground‐dwelling arthropods on two habitats (crop field and desert steppe) confirmed this conclusion when comparing estimation from TCM and NCA with densities obtained from the SSM.TCM is a promising technique for the density estimation of ground‐dwelling arthropods, especially for traps with liquid attractant and areas with relatively homogenous habitat and away from habitat edges.
Spillover in ökologischen Systemen, d.h. die Bewegung von Organismen über Habitatgrenzen hinweg, kann die trophischen Interaktionen und Ökosystemfunktionen lokaler Lebensgemeinschaften beeinflussen. Spillover-Effekte von halbnatürlichen Habitaten zu Agrarflächen fanden im Zusammenhang mit Ökosystemdienstleistungen einige Beachtung. Allerdings wurden Spillover-Effekte in die entgegengesetzte Richtung kaum untersucht, obwohl der Spillover von Bestäubern oder generalistischen Prädatoren für den Schutz halbnatürlicher Habitate von Bedeutung sein kann. In dieser Studie untersuchten wir die Prädationsraten von bodenlebenden Prädatoren auf 20 Kalkmagerrasen, die entweder an einen Nadelwald oder an ein Getreidefeld grenzten. Als Beute wurden 32000 Marienkäfereier auf den Kalkmagerrasen exponiert. Innerhalb der zwei Untersuchungszeiträume (Juni und August/September) waren die Prädationsraten an warmen Tagen höher als an kühlen Tagen, aber sie wurden nicht vom Untersuchungszeitraum oder der Entfernung zum Habitatrand beeinflusst. In jedem Untersuchungszeitraum fanden wir an kühlen Tagen höhere Prädationsraten auf Magerrasen, die an Nadelwälder grenzten, als auf Magerrasen, die an Getreidefelder grenzten. An warmen Tagen wurden die exponierten Eier zu großen Teilen (oft zu 100%) konsumiert. Ein Nachweis unterschiedlicher Prädationsraten in Abhängigkeit des Nachbarhabitats war deshalb an warmen Tagen nicht möglich. Die höheren Prädationsraten auf Magerrasen, die an Wälder grenzten, können mit einem Spillover von Prädatoren aus Wäldern auf die Magerrasen erklärt werden. Somit stellen halbnatürliche Habitate nicht nur Ökosystemdienstleistungen in benachbarten Habitaten bereit, sondern sind auch antagonistischen Spillover-Effekten ausgesetzt. Solche antagonistischen Spillover-Effekte sollten beim Schutz halbnatürlicher Habitate berücksichtigt werden.