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Responses of Crop Pests and Natural Enemies to Wildflower Borders Depends on Functional Group

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Abstract

Increased homogeneity of agricultural landscapes in the last century has led to a loss of biodiversity and ecosystem services. However, management practices such as wildflower borders offer supplementary resources to many beneficial arthropods. There is evidence that these borders can increase beneficial arthropod abundance, including natural enemies of many pests. However, this increase in local habitat diversity can also have effects on pest populations, and these effects are not well-studied. In this study, we investigated how wildflower borders affect both natural enemies and pests within an adjacent strawberry crop. Significantly more predators were captured in strawberry plantings with wildflower borders versus plantings without wildflowers, but this effect depended on sampling method. Overall, herbivore populations were lower in plots with a wildflower border; however, responses to wildflower borders varied across specific pest groups. Densities of Lygus lineolaris (Tarnished Plant Bug), a generalist pest, increased significantly in plots that had a border, while Stelidota geminata (Strawberry Sap Beetle) decreased in strawberry fields with a wildflower border. These results suggest that wildflower borders may support the control of some pest insects; however, if the pest is a generalist and can utilize the resources of the wildflower patch, their populations may increase within the crop.
insects
Article
Responses of Crop Pests and Natural Enemies
to Wildflower Borders Depends on Functional Group
Ellie McCabe 1, Gregory Loeb 2and Heather Grab 3, *ID
1Department of Biological Sciences, University of New Hampshire, Durham, NH 03824, USA;
ellieannmccabe@gmail.com
2Department of Entomology, New York State Agricultural Experiment Station, Cornell University, Geneva,
NY 14456, USA; gme1@cornell.edu
3Department of Entomology, Cornell University, Ithaca, NY 14853, USA
*Correspondence: hlc66@cornell.edu; Tel.: +1-717-364-6198
Academic Editors: Zsofia Szendrei and Amanda Buchanan
Received: 1 June 2017; Accepted: 20 July 2017; Published: 25 July 2017
Abstract:
Increased homogeneity of agricultural landscapes in the last century has led to a loss of
biodiversity and ecosystem services. However, management practices such as wildflower borders
offer supplementary resources to many beneficial arthropods. There is evidence that these borders
can increase beneficial arthropod abundance, including natural enemies of many pests. However,
this increase in local habitat diversity can also have effects on pest populations, and these effects
are not well-studied. In this study, we investigated how wildflower borders affect both natural
enemies and pests within an adjacent strawberry crop. Significantly more predators were captured
in strawberry plantings with wildflower borders versus plantings without wildflowers, but this
effect depended on sampling method. Overall, herbivore populations were lower in plots with a
wildflower border; however, responses to wildflower borders varied across specific pest groups.
Densities of Lygus lineolaris (Tarnished Plant Bug), a generalist pest, increased significantly in plots
that had a border, while Stelidota geminata (Strawberry Sap Beetle) decreased in strawberry fields with
a wildflower border. These results suggest that wildflower borders may support the control of some
pest insects; however, if the pest is a generalist and can utilize the resources of the wildflower patch,
their populations may increase within the crop.
Keywords: wildflower planting; pests; natural enemies; functional group
1. Introduction
Complex agricultural landscapes support a diverse community of beneficial insects and
ecosystem services that in turn support crop productivity [
1
4
]. Yet, for most of the 20th century
agricultural landscapes have become increasingly homogeneous due to increased expansion of
specialized, monoculture production systems [
5
]. Loss of diversity and structural complexity from
agro-ecosystems is one of the primary drivers of declines in biodiversity and associated ecosystem
services worldwide [
6
,
7
]. In particular, the loss of habitat diversity in agro-ecosystems leads to
a reduction in the abundance and diversity of beneficial insects including pollinators and natural
enemies [
4
,
8
10
]. In recent years, there has been significant interest in practices that increase farmland
diversity in ways that restore ecosystem services while maintaining crop productivity [7,11,12].
One practice that has been explored in a number of cropping systems is the addition of wildflowers
to crop borders. Wildflowers provide resources to natural enemies of crop pests including shelter
from disturbance and overwintering habitat as well as a source of nectar, pollen, and alternative
prey [
13
,
14
]. Wildflower borders have been found to increase predator populations in the crop when
planted next to blueberries [
15
,
16
], cabbage [
17
,
18
], wheat [
19
,
20
] and tomato [
21
]. Nevertheless,
Insects 2017,8, 73; doi:10.3390/insects8030073 www.mdpi.com/journal/insects
Insects 2017,8, 73 2 of 8
wildflower plantings are not always successful at increasing natural enemy populations [
22
24
] due to
both local and landscape level effects [
25
]. Landscape level effects include lack of a source population
of natural enemies in the surrounding habitat or that natural habitat surrounding the crops can be too
small and/or too far away for natural enemies to colonize the wildflower and crop habitats [
25
27
].
Local effects include farm management practices that can affect the establishment of natural enemies
such as the use of broad-spectrum insecticides [28].
The addition of wildflower plantings in field margins can also have direct effects on crop pests.
Wildflower borders may be a source for pest populations as well as beneficial insects. Pests can use the
strips as refuge from disturbances or as overwintering sites. Generalist pests can feed on the flowering
plant species throughout the summer [
29
]. In cases where wildflowers are a better resource for pests
than they are for natural enemies, the population of pests in the wildflower border may spill over into
the crop and increase crop damage. However, not all pests are expected to benefit from wildflower
borders. Specialist pests that do not utilize the wildflowers as a resource for habitat or food may be
negatively affected by the increased local plant diversity by interfering with host plant location [
30
,
31
].
In this study we explore the effect of adding wildflower borders to strawberry (Fragaria x ananassa)
plantings on natural enemy and pest populations. Lygus lineolaris Say (Tarnished Plant Bug; Hemiptera:
Miridae) and Stelidota geminata Say (Strawberry Sap Beetle; Coleoptera: Nitidulidae) are two of the
most economically significant pests of strawberries grown in the Northeastern USA, therefore we have
explicitly evaluated their populations separately from other herbivores surveyed.
The tarnished plant bug, L. lineolaris, is a generalist pest known to feed on over 300 species of
plants [
32
]. Without control efforts, it can damage up to two-thirds of a strawberry crop [
33
]. L. lineolaris
overwinters in protected areas including leaf litter, hedgerows, or plant debris [
34
] and higher densities
have been observed in blueberry and tomato fields with wildflower borders [
16
,
35
]. Alternatively
S. geminata, a fruit-feeding specialist, does not appear to benefit from wildflower plantings [
16
].
S. geminata has increased as a pest in strawberries due to the operation of pick-your-own strawberry
fields that leave ripe strawberries in the field [
36
]. Despite its common name, S. geminata is not a
specialist of strawberry; the adult and larva feed on ripe fruit of many different genera including crops
such as raspberry, blueberry, apple, melon, and sweet corn [
37
]. Adults overwinter in wooded areas or
in blueberry and raspberry plantings [
38
]. Predator prey relationships are not well described for either
species with the exception of specialist parasitoids [
39
,
40
]. The eggs, immatures and adults of both
species are not known to be chemically protected and would be an appropriate sized prey for carabids,
spiders, huntsman and other generalist arthropod predators
In this study, we hypothesized that (1) natural enemy abundance will be greater in crop plantings
with a wildflower margin compared to control plots without a wildflower border; and (2) the
abundance of the generalist pest, L. lineolaris, will remain stable or even increase in crop plantings with
adjacent wildflower borders, while S. geminata, a pest that does not utilize the floral resources of a
wildflower strip, will decrease in crop plantings with adjacent wildflower borders.
2. Methods
The study was conducted in the summer of 2014 on six research farms in the area around the
New York State Agricultural Experiment Station in Geneva, NY, USA. On each farm, two 10
×
15 m
experimental plots consisting of five rows of strawberry (var. “Jewel”) were established in the spring
of 2012. Plots were managed without use of fungicides or insecticides and weeded by hand with the
exception of a pre-emergent herbicide applied in the fall of 2013. Plots were separated by a minimum of
200 m and were randomly assigned to either a control border or a native perennial wildflower planting.
Composition and management of control borders were representative of field edge management
practices in the region and consisted primarily of orchard grass (Dactylis glomerata L.; Poaceae), which
was regularly mown over the growing season. Wildflower borders were established in the fall of 2012
along the edge of one of the outside rows of the strawberry plantings. Wildflower plantings were 4 m
wide by 10 m long and consisted of the following 11 US native perennial species: Zizia aurea (Apiaceae),
Insects 2017,8, 73 3 of 8
Penstemon digitalis (Plantaginaceae), Coreopsis lanceolata (Asteraceae), Potentilla fruticosa (Rosaceae),
Vironicastrum virginicum (Plantaginaceae), Agastache nepetoides (Laminaceae), Silphium perfoliatum
(Asteraceae), Lobelia siphilitica (Campanulaceae), and Solidago altissima (Asteraceae). These species
were selected based on their attractiveness to beneficial insects [
41
,
42
] and provide overlapping bloom
periods so that flowers are present throughout the growing season.
Pest surveys were conducted in each strawberry planting during the fruit ripening period in
June 2014. This period was selected because it is the window in which damage caused by these fruit
feeding pests occurs. All plots were sampled on the same day. Insects were collected by vacuuming
once along all five rows of each planting for approximately 5 minutes with a modified D-VAC type
suction sampling device (Echo ES 230 Shred ‘n Vac, Lake Zurich, IL, USA, 20 cm cone diameter).
The contents of the sample were placed in an ethyl acetate kill jar before being frozen at
20
C.
Frozen samples were later sorted and known economically important pests including L. lineolaris and
S. geminata were identified to species. All remaining arthropods were identified to order or family and
then placed into functional groups based on the predominant life history exhibited by their taxonomic
group (i.e., herbivorous or predacious).
Additionally, pitfall traps were deployed between strawberry rows (n = 4) in each plot to
better characterize the ground dwelling insect communities. Functionally important predators in the
system such as spiders and carabid beetles are more likely to be collected by this method [
43
45
].
Therefore, vacuum and pitfall samples were used as complimentary methods to estimate natural
enemy community composition. Pitfall traps consisted of 16 oz SOLO brad cups set flush with the soil
surface and filled with 50 mL of a 5% dish soap killing solution. Traps were deployed over a three-day
period once in each plot.
To determine the impact of wildflower strips on the abundance of different functional groups
we used generalized linear mixed effect models with a poison error distribution. Response variables
included the abundance of each functional group or taxa and fixed effects included the interaction
between functional group class and plot treatment (wildflower border or control). Random effects
included treatment within farm to account for the nested experimental design. Abundances from
vacuum samples and pitfall traps were modeled separately. Pairwise contrasts for the difference
between abundances in control and wildflower treatments plots were performed using the pairs
function and the lsmeans package in R. Differences in community composition between sampling
types and crop border treatments were assessed using permutational-MANOVA with 999 permutations
on Bray-Curtis dissimilarities.
3. Results
Vacuum sampling within the strawberry plantings revealed that wildflower strip borders had
different, sometimes opposing effects, depending on the pest species and functional group (functional
group x treatment F
(3,5)
= 14.79, p= 0.006). Strawberry plantings with a wildflower border had fewer
S. geminata per sample (z-ratio = 2.961, p= 0.003; Figure 1a) but a greater number of L. lineolaris
(z-ratio =
2.677, p= 0.007; Figure 1b). The number of other herbivores collected in plots with a
wildflower border was also lower (z-ratio = 6.525, p< 0.0001; Figure 1c) but the number of predators
was not different between control plots and plots with a wildflower border (z-ratio =
1.150, p= 0.25;
Figure 1d). The most abundant herbivore groups included Rhyparochromidae (8.1%), Cicadellidae
(6.3%), L. lineolaris (4.4%) and S. geminata (4.2%). The most abundant predators sampled by vacuuming
included Araneae (14.8%), Formicidae (7.3%) and Opiliones (5.1%).
Pitfall sampling revealed no differences in the abundance of all herbivores in strawberry plantings
with a wildflower border compared to controls (F
(1,5)
= 0.07, p= 0.79; Figure 2a). However, predator
abundances estimated by pitfall traps were greater in plots with a wildflower border (F
(1,5)
= 13.15,
p= 0.015; Figure 2b). The most abundant herbivores collected in pitfall traps included S. geminata
(3.9%), Cicadellidae (3.7%) and Aphididae (1%), while the most abundant predators included Araneae
(15.9%), Opiliones (6.7%), Formicidae (3.6%) and Carabidae (2.7%).
Insects 2017,8, 73 4 of 8
Although community composition varied strongly by sampling method (F
(1,67)
= 27.26, p= 0.001),
there was no significant difference in community composition between border treatments (
F(1,67) = 1.38
,
p= 0.13).
Insects 2017, 8, 73 4 of 8
Figure 1. Mean (±SE) abundance of two pests. (a) strawberry sap beetle (Stelidota geminata); (b)
tarnished plant bug (Lygus lineolaris); as well as (c) other herbivores and (d) predators sampled by
vacuum from plots with a control or wildflower border.
Figure 2. Mean (± SE) abundance of (a) herbivores and (b) predators sampled from pitfall traps in
strawberry plantings with and without a wildflower border.
4. Discussion
Our findings reveal that wildflower strips have differing effects on pest populations within the
crop. As hypothesized, populations of L. lineolaris, a generalist feeder, were greater in strawberry
plantings with wildflower borders. However, S. geminata, which has a narrower feeding niche, was
less abundant in plots with a wildflower border in accordance with our predictions. This suggests
the possibility that the feeding niche of a pest is a predictor of how wildflower borders will affect the
pests’ populations in the crop. For generalists such as L. lineolaris, the positive effect of additional
food resources may outweigh the negative impacts of increased natural enemies associated with the
wildflower borders.
The number of predatory arthropods collected in vacuum samples was not significantly affected
by the wildflower border, but pitfall traps revealed greater predator abundances in plots with a
0
2
4
6
8
10
12
Control Wildflower
Herbivores
0
2
4
6
8
10
12
Control Wildflower
Predators
0
0.5
1
1.5
2
2.5
Control Wildflower
Sap Beetle
0
0.5
1
1.5
2
2.5
Control Wildflower
Tarnished Plant Bug
0
1
2
3
4
5
Control Wildflower
Other Herbivores
0
1
2
3
4
5
Control Wildflower
Predators
a) b)
c) d)
* *
*
a) b)
*
Figure 1.
Mean (
±
SE) abundance of two pests. (
a
) strawberry sap beetle (Stelidota geminata);
(
b
) tarnished plant bug (Lygus lineolaris); as well as (
c
) other herbivores and (
d
) predators sampled by
vacuum from plots with a control or wildflower border.
Insects 2017, 8, 73 4 of 8
Figure 1. Mean (±SE) abundance of two pests. (a) strawberry sap beetle (Stelidota geminata); (b)
tarnished plant bug (Lygus lineolaris); as well as (c) other herbivores and (d) predators sampled by
vacuum from plots with a control or wildflower border.
Figure 2. Mean (± SE) abundance of (a) herbivores and (b) predators sampled from pitfall traps in
strawberry plantings with and without a wildflower border.
4. Discussion
Our findings reveal that wildflower strips have differing effects on pest populations within the
crop. As hypothesized, populations of L. lineolaris, a generalist feeder, were greater in strawberry
plantings with wildflower borders. However, S. geminata, which has a narrower feeding niche, was
less abundant in plots with a wildflower border in accordance with our predictions. This suggests
the possibility that the feeding niche of a pest is a predictor of how wildflower borders will affect the
pests’ populations in the crop. For generalists such as L. lineolaris, the positive effect of additional
food resources may outweigh the negative impacts of increased natural enemies associated with the
wildflower borders.
The number of predatory arthropods collected in vacuum samples was not significantly affected
by the wildflower border, but pitfall traps revealed greater predator abundances in plots with a
0
2
4
6
8
10
12
Control Wildflower
Herbivores
0
2
4
6
8
10
12
Control Wildflower
Predators
0
0.5
1
1.5
2
2.5
Control Wildflower
Sap Beetle
0
0.5
1
1.5
2
2.5
Control Wildflower
Tarnished Plant Bug
0
1
2
3
4
5
Control Wildflower
Other Herbivores
0
1
2
3
4
5
Control Wildflower
Predators
a) b)
c) d)
* *
*
a) b)
*
Figure 2.
Mean (
±
SE) abundance of (
a
) herbivores and (
b
) predators sampled from pitfall traps in
strawberry plantings with and without a wildflower border.
4. Discussion
Our findings reveal that wildflower strips have differing effects on pest populations within the
crop. As hypothesized, populations of L. lineolaris, a generalist feeder, were greater in strawberry
plantings with wildflower borders. However, S. geminata, which has a narrower feeding niche, was less
abundant in plots with a wildflower border in accordance with our predictions. This suggests the
possibility that the feeding niche of a pest is a predictor of how wildflower borders will affect the
Insects 2017,8, 73 5 of 8
pests’ populations in the crop. For generalists such as L. lineolaris, the positive effect of additional
food resources may outweigh the negative impacts of increased natural enemies associated with the
wildflower borders.
The number of predatory arthropods collected in vacuum samples was not significantly affected by
the wildflower border, but pitfall traps revealed greater predator abundances in plots with a wildflower
border. These differences likely reflect an increase in ground dwelling predators, most notably carabids,
which comprised a greater percentage of the community in pitfall compared to vacuum samples. It is
important to point out that in this study only the arthropod populations within the crop were examined;
therefore we cannot rule out that natural enemy populations were not greater in the wildflower borders
compared to the control borders. Indeed, prior studies have shown that natural enemies inside the
wildflower border itself can increase more than the population within the crop [
15
,
16
]. These predators
in the crop borders may reduce pest migration into the crop.
Overall populations of herbivores in strawberry plantings with an adjacent wildflower planting
were lower than those in control plantings. Lower herbivore numbers may have occurred through
top-down effects from the increase in ground-dwelling predators and/or through bottom-up effects on
herbivores by decreasing host plant apparency [
31
,
46
]. L. lineolaris populations increased in strawberry
plots with wildflower borders. Similar effects have also been recorded in blueberry plantings with
an adjacent wildflower planting of similar composition [
16
] and in tomato with a diverse wildflower
border [
35
]. We propose that the positive response of L. lineolaris to the wildflower border is because
of its generalist feeding niche. L. lineolaris is likely attracted to and utilizes the wildflowers as a food
source and as a bridge to move from surrounding habitats into the strawberry crop. When a generalist
is the key pest, the addition of wildflowers may be counter-productive and growers might need to
turn to other methods of control. It is important to note however, that the greater number of nymphs
observed in plantings with a wildflower border may not result in increases in crop damage. Future
studies should explore the potential for flowering strips to impact crop damage or to reduce benefits
from other services, such as pollination that may benefit from wildflower strip management.
Similar to the decrease of herbivores overall, S. geminata decreased in strawberry plots with a
wildflower border. We suggest that the difference in abundance between treatments for S. geminata
may be due to increased habitat complexity interfering with host finding behavior and residence time,
or through increased predation rates. S. geminata feeds on ripe fruits resting on the ground and is
therefore potentially susceptible to ground-dwelling predators. S. geminata in the strawberry crop may
be affected by both bottom-up and top-down factors [
30
,
31
]. Because it is likely that both L. lineolaris
and S. geminata could utilize the wildflower plantings as overwintering habitats this suggests that
the differential responses to wildflower borders are primarily mediated by differences in feeding
preferences or foraging behavior.
5. Conclusions
The effects of wildflower borders on pests have important implications for farmers and integrated
pest management programs. As more farmers and integrated pest management (IPM) programs
implement wildflower borders into their plans for conserving pollinators and natural enemies, they
also need to consider how pests are responding. This study suggests that wildflower borders can
increase ground-dwelling predators within the crop and decrease the abundance of economically
significant pests overall. However, when the main pest can use the resources in the wildflower border,
spillover of pests from wildflower plantings may lead to an increase in their population within the
crop, and alternative methods of control will be needed to regulate these pests.
Acknowledgments:
We thank three anonymous reviewers for improvements to the manuscript. We also thank
Alison Wentworth and Steve Hesler for their assistance in the field. Ellie McCabe thanks the New York State
Agricultural Experiment Station’s Summer Research Scholars Program for funding and support to conduct this
research. This work was supported in part by a Northeast SARE graduate student grant to HG (GNE12-036).
Insects 2017,8, 73 6 of 8
Author Contributions:
All authors designed the experiments, Ellie McCabe and Heather Grab conducted
the experiment, Heather Grab analyzed the data, Ellie McCabe and Heather Grab wrote the manuscript and
Gregory Loeb edited the manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... Wildflower plantings may also increase biological control of agricultural pests provided by arthropod predators. Increased arthropod predator abundance has been found within blueberry and strawberry fields that contained adjacent wildflower plantings (Walton and Isaacs 2011, Blaauw and Isaacs 2015, McCabe et al. 2017. Wildflower plantings also can be used to ❖ www.esajournals.org 2 October 2019 ❖ Volume 10(10) ❖ Article e02890 promote biological control of pest lepidopterans in cabbage fields (Pfiffner et al. 2009) and potentially contain more beneficial predatory arthropods than do turf grass plots (Braman et al. 2002). ...
... However, how these predatory arthropods control specific pest species remains unknown. Higher abundances of predatory insects have been found in crops with wildflower plantings planted adjacent to them (Woltz et al. 2012, Blaauw and Isaacs 2015, McCabe et al. 2017) and in agricultural fields with more surrounding landscape diversity (Gardiner et al. 2009). Additionally, many of the adult predatory wasps collected in this study (e.g., Crabronidae, Tiphiidae) also drink nectar from flowers and thus may have been attracted to the wildflower plots for their increased floral resources. ...
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Intensive agriculture has led to a reduction of overall biodiversity and ecosystem services such as pollination and biological control. To offset these economic losses, many farmers are planting native wildflowers to enhance flowering plant diversity and augment pollinator and other beneficial arthropod populations on their farms. In this study, we examined arthropod communities in Florida (USA) within wildflower plots and fallow control plots, which were primarily composed of grasses. Significantly more herbivorous insects, predatory arthropods, and pollinators were found within wildflower plots than in fallow control plots. We also implemented pollinator surveys at flowering plants. These surveys highlighted numerous plant-pollinator interactions within wildflower plots, supporting the idea that some native wildflower species are more attractive to pollinators than are others. Nevertheless, utilizing diverse flowering plants for wildflower plots may support a wide diversity of beneficial arthropod species, including native bees. Our results suggest that wildflower plantings in Florida can be a successful management tool to harbor increased overall plant and arthropod diversity (including native pollinators and other beneficial arthropods) within intensive agricultural areas.
... One approach that has been seen as especially effective is the planting of flowers (https://www.conservationevidence. com/actions/442, Meek et al. 2002, Powell et al. 2004, Boller et al. 2004, van Rijn et al. 2008, Hogg et al. 2011, Blaauw and Isaacs 2012, Balmer et al. 2013, Varennes 2015, Tschumi et al. 2016, Campbell et al. 2017, Hatt 2017, McCabe et al. 2017, Pfister 2017, Sutter et al. 2018, Cipkowski 2019, Pollier et al. 2019, Rodríguez-Gasol et al. 2019, but see Poveda et al. 2008 for comparison with other diversification techniques and see Phillips andGardiner 2015 andQuinn et al. 2017 for contrasting results). Flowers themselves can provide pollen and nectar resources not only to pollinators, thereby helping to tide them over food shortages, but also to parasitoid wasps, who as adults feed upon nectar. ...
... Our prediction was that our flower-rich seed mix would attract more beneficial insects than the other treatments. At the same time our hope, if not an explicit prediction, was that that seed mix would not also increase pest populations dramatically (but see Winkler et al. 2010, dos Santos 2017, McCabe et al. 2017. Together with the increase in beneficials, we predicted that we would see an increase in agroecological services such as pest predation and, finally, that crops planted adjacent to our flower-rich seed mix would, if anything, have greater production. ...
Technical Report
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Report on several years of agroecological study of the effects of perennial wildflowers and forest edge on insects and spiders on a Mid-Hudson Valley Farm.
... The potential of WFS as overwintering habitat for arthropods may, however, depend on the type and age of the WFS due to successional changes in vegetation and soil properties over time (Frank and Reichhart, 2004). Such properties may include the proportion of bare soil, plant species composition and diversity or soil characteristics such as bulk density (McCabe et al., 2017;Sarthou et al., 2014;Sutter et al., 2018b). Such successional changes in overwintering habiat properties along with the absence of disturbance by farming activities over the years may favour overwintering of arthropods (Frank and Reichhart, 2004;Pfiffner and Luka, 2000) resulting in a positive linear or saturating relationship between WFS age and overwintering of arthropods (Frank and Reichhart, 2004). ...
... We focused on these two local vegetation characteristics because they have been identified as potential key drivers of arthropod overwintering in previous studies (e.g. McCabe et al., 2017;Sarthou et al., 2014;Sutter et al., 2018b) and because they represent simple characteristics for different types and successional stages of WFS that can be readily assessed and communicated to farmers interested in improving the potential of their WFS with respect to beneficial arthropod overwintering. ...
Article
Wildflower strips (WFS) are increasingly commonly adopted measures to promote biodiversity in agro-ecosystems. While their effectiveness in providing floral and other food resources for pollinators and natural enemies has been relatively well studied, much less is known about the value of different types of WFS as overwintering habitat for different functional arthropod groups. Here, we examined arthropod overwintering in WFS of different age compared to winter wheat fields. Moreover, we addressed the largely unexplored question to what extent non-permanent WFS may act as sink or ecological trap, if they attract high numbers of overwintering arthropods but only a low proportion of them survive and successfully emerge due to ploughing of strips during overwintering. Overwintering of all studied arthropod groups eincluding potential pest natural enemies spiders, carabid beetles, staphylinid beetles and different families of pollinating flies ewas higher in WFS compared to winter wheat crops. Overwintering increased in WFS compared to wheat fields irrespective of WFS age, except for 4 year old WFS in the case of carabid beetles and 1 year old WFS in the case of spiders. While WFS age positively affected spider overwintering, numbers of overwintering pollinating flies and staphylinid beetles did not change significantly with WFS age. Moreover, carabid beetles tended to decline in the four years old WFS compared to younger ones. Ploughing of annual WFS during overwintering significantly reduced the number of successfully emerging arthropods by 59% on average. Detrimental effects were strongest for carabid beetles and spiders (reductions by 67% and 69%, respectively) to their numbers in ploughed WFS being similar to winter wheat fields. Reductions were less severe for pollinating flies and staphylinid beetles (both 47%), with higher numbers emerging from annual WFS compared to winter wheat fields even after ploughing of WFS. We conclude that perennial WFS are valuable overwintering habitats for a range of arthropod taxa across functional groups in arable cropping systems. Distinct responses of different arthropod taxa to WFS age highlight the importance of managing perennial WFS of various successional stages in order to promote overwintering of a broad variety arthropods in agro-ecosystems. Our study raises concerns, however, that annual WFS ploughed during the overwintering period are poor overwintering habitats for arthropods and may even act as ecological traps.
... Blaauw and Isaacs (2015) reported greater abundance of natural enemies in blueberries adjacent to wildflower plantings. Like us, McCabe et al. (2017) found that, in vacuum sampling, predatory insects did not increase in strawberries adjacent to wildflower plantings, although certain pests (such as Tarnished plant bug) responded positively. Their pit trapping (which we have not yet conducted in the vegetable beds) did suggest an increase in predators. ...
Technical Report
Full-text available
This report details five years of work following the invertebrates of wildflower trial meadows at the Hudson Valley Farm Hub, near Hurley NY. For accompanying botanical report, please see: https://hvfarmscape.org/sites/default/files/native_meadow_trials_at_the_hudson_valley_farm_hub_5_year_report.pdf
... By providing a rich community of plant species, insect conservation plantings on farms can support diverse insect communities, although the majority of responding bee species may be the more common ones that also provide most of the ecosystem services rather than rare species that are of more acute conservation concern (Kleijn et al., 2015). Wildflower plantings may also attract pest insects that use particular flowering species (McCabe, Loeb, & Grab, 2017), requiring an understanding of the pest complex before applying this approach for enhancing crops. ...
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Designing wildflower habitats to support beneficial insects providing pollination and pest control services is important for supporting sustainable crop production. It is often desirable to support both groups of insects, making the selection of resource plants for insect conservation programs more challenging. Moreover, the process of selecting resource plants is complicated by the array of possible options in each region, and the need to provide resources over the entire growing season. Identifying traits shared by resource plants that are attractive to both bees and natural enemies can reduce the need to evaluate new plants in each region, by providing a guide for the types of plants expected to be rewarding to these insects. Using insect visitation data collected from replicated common garden plantings of native wildflower and shrub species from the Great Lakes region of the United States, we found a high degree of correlation between the abundance of bees and natural enemies visiting native plant species. These results were used to identify a set of 15 plant species that can provide resources for these insects throughout the summer. Across all tested species, pollen quantity per flower and the week of bloom were positively correlated with some, but not all, taxonomic groupings of beneficial insects. In contrast, floral area was consistently positively associated with visitation of both natural enemies and wild bees. This trait is easy to document and can allow for efficient local testing of potential resource plants, providing a faster path to implementing insect conservation in working landscapes.
... The diversity of arthropods in freshwater swamps is also supported by the existence of wild flowering weeds or non-crop plants like refugia grown surrounding the rice field. These plants provide niche, additional food, and other resources for natural enemies of rice pests (Benvenuti & Bretzel, 2017;de Faria Lopes, Ramos, & de Almeida, 2017;Hassan, Pervin, Mondal, & Mala, 2016;McCabe, Loeb, & Grab, 2017;Zhu et al., 2015). Grassy rice fields in ecosystems have a higher number of arthropods than those in non-weed ecosystems (Hu et al., 2012). ...
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The plants surrounding rice field serve as a habitat and niche for entomophagous arthropods. This study aimed to identify the entomophagous arthropod species and to analyze their abundance and community in vegetables and refugia grown in the rice field. The field was surrounded by 4 species of refugia (Zinnia sp., Tagetes erecta, Cosmos caudatus, and Sesamum indicum) and 4 species of vegetables (Vigna unguiculata, Momordica charantia, Cucumis sativus, and Luffa acutangula). The arthropod found were 67 species of predatory arthropods and 22 species of parasitoids. The predatory arthropods were mostly found in rice (51 species) followed by Zinnia sp. (15 species), and M. charantia (9 species). Parasitoid species were dominantly found in rice (19 species), Zinnia sp. (7 species), and M. charantia (6 species). The predatory arthropods mostly found were Tetragnatha javana, Tetragnatha virescens, and Paederus fuscipes, while the dominant parasitoids were Cardiochiles sp., Elasmus sp., and Snellenius sp. The parasitoid species composition in rice was more similar to those in bitter melon and zinnia. The composition of predatory arthropod species in rice was similar to those in all vegetables and refugia, except in cowpea. Zinnia sp. and M. charantia were the most chosen habitat by entomophagous arthropods.
Technical Report
Crop diversification aims to increase the diversity of crops grown at different times and scales at the farm. Such practices play an essential role in organic agriculture, representing real potential that is yet to be leveraged. Solid research results have proven the agronomic and environmental benefits of crop diversification on agricultural systems compared to monoculture. Indeed, by maximising synergies between the crops grown together (e.g. intercropping), or after each other (e.g. crop rotation), on the same field, organic farmers can maintain crop and soil health and ensure that fields can be arable in the long term with a good yield. Crop diversification practices also contribute to diversified and more resilient income sources for farmers, which gives them the opportunity to sustain their businesses and invest in their family’s future. For a cotton farmer, producing organically means moving from a crop centric approach towards a cropping system approach, and from an input-based production logic towards knowledge-based farming. Knowledge is the key to unlocking the benefits of organic cotton-based farming systems. Hence, improving the business case for organic cotton farming in India means bridging the knowledge gap on crop diversification and considering the profitability of the whole farming system.
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Because of high-value, the crops like Brassica have very low pest-damage thresholds, natural enemies alone are unlikely to replace use of high cost insecticides. However, conservation of natural enemy population is possible by avoiding or applying insecticides at reduced rates and use of habitat manipulation techniques such as ecological engineering, used in the present research work. The selected flower crops apart from hosting natural enemy it is also an alternate source of income to farmers. Among the intercrops, cineraria flower crop reported with less number of aphids and even attracted more number of syrphids as well as coccinellids can be exploited to use as intercrop.
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Current agroecosystem management practices have a negative effect on natural enemies and their ability to control insect pests. Conservation biological control through the addition of flowering resources can manage food resources for natural enemies. These floral resources can also provide multiple ecosystem services. Study goals were to determine if perennial Thymus vulgaris L. was attractive to natural enemies and if so, could it be a dual use resource encouraging pest management and providing harvestable product. In 2018 plots in three locations were used to examine the effect of habitat throughout the growing season on the attractiveness of T. vulgaris. Large numbers of Thysanoptera and Hemiptera were collected in all locations, represented by phytophagous Aphididae and Thripidae, and predatory Anthocoridae. Location influenced other families to varying degrees. Seasonal specimen counts were influenced by vegetation density, floral phenology, and predator/prey relationships. In 2019 replicated plots of three treatments were used to examine if harvesting plant material affected the attractiveness of T. vulgaris to natural enemies. Total specimens in 2019 were not significantly different among treatments, indicating removal of blooms did not significantly affect the attractiveness of T. vulgaris. Significant numbers of Thysanoptera and Hemiptera were again collected in all treatments, represented by phytophagous Aphididae and Thripidae. Greater numbers of Diptera and Hymenoptera were also collected. Significant numbers of Thripidae, Aphididae, Mymaridae, and Platygastridae were found in the Family level analyses. Results from both years indicate T. vulgaris was attractive to natural enemy and phytophagous Families. Data from 2018 suggest natural enemy families were attracted to alternative prey and hosts utilizing the foliage rather than flowers but the use of nectar and pollen cannot be ruled out. Data from 2019 suggest the presence of flowers played an important role in the attractiveness of T. vulgaris to micro-hymenopteran parasitoids, Syrphidae, and native Apidae. In conclusion, Thymus vulgaris has the potential to be a dual use floral resource that benefits growers through supporting native enemy populations and pollination services, as well as provide income from the harvest of foliage. It could also be used as a beneficial, harvestable floral resource in urban gardens to encourage pollinator conservation and natural pest control.
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The influence of local and landscape habitat diversification on biological control of the Western grape leafhopper (Erythroneura elegantula Osborn) by its key parasitoids Anagrus erythroneurae S. Trjapitzin & Chiappini and Anagrus daanei Triapitsyn was studied in wine grape vineyards. At the landscape scale, Anagrus rely on alternative host species in non-crop habitats outside of the vineyard to successfully overwinter, while at the local scale vineyard diversification can provide resources, such as shelter and floral nectar, which improve parasitoid performance. In a two-year experiment, plots with and without flowering cover crops were compared in vineyards representing a gradient of landscape diversity. While the cover crops did attract natural enemies, their populations were unchanged in the crop canopy and there was no difference in parasitism rate, leafhopper density, crop quality, or yield. Vineyards in diverse landscapes had higher early-season abundance of Anagrus spp., which was linked to increased parasitism and decreased late-season populations of E. elegantula. Leafhopper densities were also positively associated with crop vigor, regardless of landscape or cover crops. Flowering cover crops did increase abundance of some natural enemy species as well as parasitism rate in vineyard landscapes with intermediate levels of diversity, indicating a local × landscape interaction, although this did not lead to reductions in E. elegantula densities. These findings indicate that, in this agroecosystem, landscape diversity mediates and in many ways outweighs the influence of local diversification and that E. elegantula densities were regulated by a combination of biological control and crop vigor.
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Providing key resources to animals may enhance both their biodiversity and the ecosystem services they provide. We examined the performance of annual flower strips targeted at the promotion of natural pest control in winter wheat. Flower strips were experimentally sown along 10 winter wheat fields across a gradient of landscape complexity (i.e. proportion non-crop area within 750 m around focal fields) and compared with 15 fields with wheat control strips. We found strong reductions in cereal leaf beetle (CLB) density (larvae: 40%; adults of the second generation: 53%) and plant damage caused by CLB (61%) in fields with flower strips compared with control fields. Natural enemies of CLB were strongly increased in flower strips and in part also in adjacent wheat fields. Flower strip effects on natural enemies, pests and crop damage were largely independent of landscape complexity (8-75% non-crop area). Our study demonstrates a high effectiveness of annual flower strips in promoting pest control, reducing CLB pest levels below the economic threshold. Hence, the studied flower strip offers a viable alternative to insecticides. This highlights the high potential of tailored agri-environment schemes to contribute to ecological intensification and may encourage more farmers to adopt such schemes. © 2015 The Author(s).
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Cucurbit crops are attacked by a pest complex that threatens production via direct feeding and disease transmission. The goals of this study were to quantify the amount of biocontrol service supplied to pumpkin fields and determine if this was affected by local habitat management or the surrounding landscape. Using sentinel eggs, we measured predation of squash bug, Anasa tristis, and spotted cucumber beetle, Diabrotica undecimpunctata howardi, by generalist predators. We found that predators significantly removed D. undecimpunctata howardi but not A. tristis eggs. The guild of predators found to attack D. undecimpunctata howardi included Araneae, Carabidae, Cricetidae, Entomobryidae, Formicidae, Gryllidae and Opiliones. A smaller, but overlapping guild of predators was found to attack A. tristis, which included Araneae, Cricetidae, Formicidae and Gryllidae. Formicidae was consistently the dominate predator of both pest species. We examined how the addition of either a non-native annual plant insectary of sweet alyssum, Lobularia maritima, or a diverse insectary planted with native perennial forbs and grasses influenced predator abundance, composition, or biocontrol services relative to a grass control. We found no difference in either the predator community feeding on pest eggs or the proportion of eggs that they removed from adjacent pumpkin fields. Larger-scale landscape composition did influence the amount of egg predation occurring in pumpkin agroecosystems, however, these relationships varied among pests and across years of the study. Biological control is commonly predicted to increase with landscape diversity and the amount of non-crop habitat present surrounding focal fields, yet we found that when landscape did influence egg predation it was agricultural landscapes supporting the highest egg removal. This study illustrates that patterns relating landscape and localized habitat management to crop pest predation are not constants, they can vary among years within a crop as well as among agricultural cropping systems.
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1. The expansion of intensive agricultural practices is a major threat to biodiversity and to the delivery of ecosystem services on which humans depend. Local-scale conservation management strategies, such as agri-environment schemes to preserve biodiversity, have been widely adopted to reduce the negative impacts of agricultural intensification. However, it is likely that the effectiveness of these local-scale management actions depend on the structure and composition of the surrounding landscape. 2. We experimentally tested the utility of floral resource strips to improve local-scale biological control of crop pests, when placed within a gradient of moderately simple through to highly complex landscapes. 3. We found that experimental provision of floral resources enhanced parasitism rates of two globally important crop pests in moderately simple landscapes but not in highly complex ones, and this translated into reduced pest abundances and increased crop yield. 4. Synthesis and applications. Our results lend experimental support for the 'intermediate landscape complexity hypothesis', which predicts that local conservation management will be most effective in moderately simple agricultural landscapes, and less effective in either very simple landscapes where there is no capacity for response, or in highly complex landscapes where response potential is already saturated. This knowledge will allow more targeted and cost-effective implementation of conservation biological control programs based on an improved understanding of landscape-dependent processes, which will reduce the negative impacts of agricultural intensification.