10.5061/DRYAD.X69P8CZF0
McHugh, Niamh Mary
0000-0001-6659-7266
Game and Wildlife Conservation Trust
Moreby, Stephen
Game & Wildlife Conservation Trust
Lof, Marjolein
Wageningen University & Research
van der Werf, Wopke
Wageningen University & Research
Holland, John
Game & Wildlife Conservation Trust
The contribution of semi-natural habitats to biological control is
dependent on sentinel prey type
Dryad
dataset
2020
Agroecology
Aphids
landscape ecology
semi-natural habitat
Sentinel
surrogate prey
European Union’s Seventh Framework Programme
311879
2020-02-10T00:00:00Z
2020-02-10T00:00:00Z
en
261999 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
It is widely recognized that landscape factors affect the biological
control of weed seeds and insect pests in arable crops, but landscape
effects have been found to be inconsistent between studies. Here, we
compare six different types of sentinels (surrogate prey that was either
live insects or seeds) to measure the effects of semi-natural habitats at
field to landscape scales on levels of biological control in winter wheat
in the UK. Sentinels were located in fields adjacent to three boundary
types: grassy margin, hedgerows or woodland to study local scale effects
and in landscapes of varying heterogeneity in study areas of 1 km radius.
Overall mean levels of predation were higher for most insect prey (60.8%)
located on the ground compared to the crop (12.2%) and was lower for seeds
(5.8%). Predation of sentinels on the ground was attributed to generalist
predators. Semi-natural habitats had both positive and negative effects at
field and landscape scales, but the response varied with the sentinel
type. Herbaceous linear semi-natural habitats had positive effects at
local scales for Calliphora vomitoria and Sitobion avenae sentinels and
provides evidence that farmers can introduce linear herbaceous features to
benefit biological control. In contrast our distance weighted kernel
models identified a positive relationship between woody habitats and the
predation of Caliphora vomitoria and Chenopodium album. Natural aphid
infestations were lower in landscapes with more semi-natural habitat.
Synthesis and applications. Sentinels may be sensitive enough to detect
variation in levels of biological control influenced by semi-natural
habitats, but this study confirms that landscape effects differ for
different types of sentinel prey. This implies that it may not be possible
to categorize landscapes as pest suppressive using a single sentinel type.
Future studies should therefore consider using multiple sentinels to give
a better perspective on predation intensity. The resulting recommendations
for farm management include planting woodland adjacent wheat fields
infested with seed predators and positioning herbaceous linear habitats
adjacent wheat fields infested with Sitobion Avenae, particularly if
fields are bordered by woody liner habitats due to their association with
decreased Sitobion Avenae predation.
Study area The study was conducted in 18 focal fields of winter wheat per
year surrounded by a 1 km radius landscape circle in the South East and
South West regions (counties Dorset and Hampshire) of the UK in 2014 and
2015 (Fig. 1). A 1 km radius was used because this was the distance over
which many previous studies had detected an infuence on biocontrol in
cereal crops (e.g. Rusch et al., 2016). The area has a temperate climate,
summers are warm and humid (Kottek et al., 2006). Due to crop rotation,
focal fields sown with winter wheat in 2014 were put into a different crop
in 2015 which prevented the use of the same focal fields and their
surrounding landscape circles in 2015. Between years, landscape circles
were, however, selected to be close together and are defined as landscape
circle pairs. The central point of landscape circle pairs were seperated
by a distance of 90 m to 3 km (mean 1.15 ± 0.05 km). Sampling design A
standardised QuESSA protocol was followed that examined the impact of
three different boundary types (local effect) on sentinel predation. From
the 18 focal fields studied each year, six had a field boundary for each
of three categories, 1) herbaceous strip between fields (control), 2)
woody linear habitat (hedgerow) or 3) woody areal habitat (woodland)
(Table A.1). Within each field, sentinels were placed at 2, 25, 48 and 71
m from the adjacent SNH, along two transects 10 m apart (Fig. A1). To
minimize the influence of the other field boundaries on transects, the
distance between the end of the transects and non-focal field boundaries
had to be at least 1.25 times the length of the transect (i.e. 88.75 m).
All SNHs within a 1 km radius of the transect centres were digitised in
Arc GIS V.10.5 (ESRI, 2011), using the Lambert Azimuthal Equal Area
geo-referencing system. SNH present in landscape circles were mapped using
the Customer Land Database (CLAD) and in-field observations, SNH were then
categorised as either herbaceous linear, herbaceous areal, woody linear,
woody areal or fallow (land which has been plowed and left unseeded for at
least one season). Areal habitats were defined as having a minimum width
of 25 m, whereas linear habitats were between 1.5 m and 25 m wide, both
areal and linear habitats were defined as having a minimum length of 50 m
and minimum surface area of 75 m2. Herbaceous habitats comprised
<30% shrub/tree cover and includes sown habitats, whilst woody
habitats had >30% shrub/tree cover. Total SNH was calculated as
the sum of these habitats. Sentinel Sampling The sentinels were deployed
on two occasions in June/July 2014 and 2015. They comprised Calliphora
vomitoria larvae (Diptera: Calliphoridae), Ephestia kuehniella eggs
(Lepidoptera: Pyralidae), Drosophila melanogaster pupae (Diptera:
Drosophilidae, one round in 2014 only), Poa trivialis seeds (Poaceae) and
Chenopodium album seeds (Amaranthaceae), which were all located on the
ground, and Sitobion avenae adults which were artifically attached to the
crop (see below). Calliphora vomitoria larvae were pinned live to strips
of 6 mm thick plastazote (1 x 10 cm), 10 per strip. To mimic Lepidoptera
egg-laying, E. kuehniella egg masses were exposed on four corners (0.25 x
0.25 cm each) of dry-stick paper (1 x 2 cm; supplied by Oecos Ltd.). The
percentage of eggless surface on each corner of dry-stick was then
estimated in the laboratory using microscopes). For the seed sentinels,
fine sandpaper (5 x 10 cm) was attached to plastazote of the same size to
provide some rigidity (Westerman et al., 2003). Twenty seeds of each
species were then attached to the sandpaper using M3 spray mount in two
blocks with a 5 x 4 arrangement. All other sentinels were attached to dry
stick card which was then coated with fine sand to allow predatory insects
to walk across the surface. Ten D. melanogaster pupae were attached to dry
stick card and placed on the ground. Ten live adult wingless apterate
cereal aphids S. avenae were attached to dry stick card and two cards were
stapled onto flag leaves at each sampling point. Natural cereal
infestation by aphids was assessed on 25 tillers at each distance along
one of the transects, on one occassion in 2014 and two occasions in 2015
when populations would be peaking in both years. All sentinels placed on
the ground were covered with a metal cage (1 cm mesh) to prevent access by
birds and rodents. Numbers of all sentinels, except for E. kuehniella,
were counted when deployed (in case any were lost in transit) and on
collection in the field. Assessments were made after 24 h for animal prey
and 7 days for seeds. Seed sentinels were left in the field for longer
than animal prey because they are not as perishable as live prey and
previous studies recommend that sampling takes place after 2 – 14 days
(Westerman et al. 2003). Partially or totally consumed prey items were
recoded as predated.