DOI: 10.5061/dryad.dz08kprzh
title: Data from: Ecological requirements drive the variable responses of wheat pests and natural enemies to the landscape context

description: 1. Semi-natural habitats (SNH) are considered essential for pest
 suppressive landscapes, but their influence on crop pests and natural
 enemies can be highly variable. Instead of SNH per se, the availability of
 resources, such as pollen and nectar, may be more relevant for supporting
 pest control. 2. Here, we assessed the spatio-temporal variation of
 multiple insect pests (cereal leaf beetles and aphids) and natural enemies
 (predators and aphid parasitoids) in wheat fields and their responses to
 landscape context and flower availability. We combined detailed
 information on pollen use by natural enemies with the specific
 distribution of pollen-providing plants across a gradient of landscape
 composition and configuration. 3. The abundance of wheat pests was tightly
 linked to wheat development stage. Syrphids colonised the fields early in
 the season, while the abundance of other enemies increased later in the
 season. The responses of pests to landscape structure were variable and,
 while some pests had low abundances in landscapes with high edge density
 and SNH cover, Sitobion avenae abundance was positively associated with
 SNH cover. Lacewings, syrphids and cereal leaf beetles were abundant in
 landscapes with diverse and abundant flower resources, whereas the
 abundance of parasitoids and Nabis sp. was driven by aphid abundance. We
 detected no significant indirect effects of landscape on pests via natural
 enemies. 4. Synthesis and applications. Our findings
 highlight the need for conservation biological control to go beyond “one
 size fits all” and consider the specific ecology of the involved
 organisms. Landscapes with high edge density and flowering woody plants
 may support natural enemies, in particular syrphids, which colonised the
 fields early in the season. Incentives for pest-suppressive landscapes
 should focus on tailored strategies that disfavour pests and
 simultaneously enhance natural enemies according to their ecological
 requirements.
description: <strong>Study
 sites</strong> We selected 19 winter wheat
 fields located in landscapes covering a gradient in landscape composition
 in terms of woody and herbaceous SNH cover, and floral resource
 availability (based on the flower resources consumed by <i>Bombus
 terrestris</i> L.; Eckerter et al., 2020). At each field, three
 transects parallel to a focal field edge were established along three
 consecutive tractor tracks, at distances ranging between 5 and 48 m from
 the edge and at a minimum distance of 50 m from other field edges. The
 mean nearest neighbour distance between focal fields was 1.9 ± 1.0 km
 (range 0.6-3.7 km). Landscape metrics were derived for circular buffers of
 radius 0.5 km around each focal edge. We assessed the nearest distances to
 forest, measures of landscape composition (proportion of forest, arable
 land, cereals, urban areas, semi-natural habitats and Shannon-Wiener index
 of crop diversity) and landscape configuration (edge density, woody edge
 density, field size and mean field size) in QGIS 3.6.2 (QGIS Development
 Team, 2019). Landscapes were digitised as polygon layers using Sentinel-2
 satellite imagery as base maps and ground-truthed in the field in May-July
 2020. <strong>Insect
 sampling</strong> Wheat pests and natural enemies
 were sampled using direct counting on wheat stems and sweep netting.
 Direct counting entailed the visual inspection of 40 wheat stems per
 transect per sampling date (for a total of 120 stems per field). Sweep-net
 sampling consisted of taking 100 sweeps per transect at 1 m intervals
 using a 30 cm diameter net. Samplings were repeated three times from May
 to early July 2020 during three wheat phenological phases (flowering, milk
 ripening, and dough phases). For pests, we assessed the
 abundance of aphids (<i>Sitobion avenae, Metopolophium
 dirhodum</i> and <i>Rhopalosiphum padi</i>) and cereal
 leaf beetles (<i>Oulema </i>spp.). The following groups and
 stages of natural enemies were recorded: lacewings
 (<i>Chrysoperla</i> spp. eggs, larvae and adults), syrphids
 (eggs and larvae), ladybeetles (larvae and adults from several species of
 Coccinellidae), predatory bugs (i.e., adult <i>Nabis</i> sp.)
 and aphid parasitoids (mummies). In addition to raw abundances, we
 calculated aphid parasitism as the number of mummies per transect divided
 by total aphid abundance. <strong>Assessment of
 floral resources</strong> We expressed the availability of
 floral resources in terms of the total area covered by flowering plants
 that could offer resources for natural enemies, the flower diversity of
 the landscapes, and a specific index considering the pollen consumed by
 <i>Chrysoperla carnea</i>. To calculate these variables,
 flowering plants in each landscape were mapped during two occasions.
 First, woody plants were mapped in 2017-2019 (See Supplementary Methods in
 the article; Eckerter et al., 2020) in sampling plots of 10x10 m covering
 all hedgerows and forest edges of each landscape. Second, herbaceous
 flowering plants were mapped in May-July 2020 along transects in all the
 edges between landscape elements (Supplementary Methods). Both data
 sources were digitised in QGIS as vector layers and the total area per
 pollen type was calculated for each landscape. Only insect-pollinated
 plants were considered as these represent sources of both pollen and
 nectar for insects and are more likely to be actively visited by natural
 enemies (Wäckers et al., 2005). Plants with tubular flowers of limited
 accessibility were excluded from all calculations (van Rijn &
 Wäckers, 2016). Total flower area was then
 calculated as the sum of the area covered by insect-pollinated mapped
 plants in each landscape. Flower diversity was calculated as the
 Shannon-Wiener Index of flower diversity, considering the relative cover
 of all insect-pollinated plants per landscape. Finally, we calculated a
 specific flower availability index (FAI) based on the pollen ingested by
 adult green lacewings collected using sticky traps in 2019 in the same
 study region (Supplementary Methods). The FAI was calculated using the
 formula developed by Eckerter et al. (2020), which sums the relative cover
 of plants providing each pollen type in each landscape times their
 proportional use by lacewings expressed as the share of total ingested
 pollen volume (Supplementary Methods). Thus, the FAI allows to compare the
 availability of pollen between landscapes, weighing the contribution of
 each pollen type according to its relevance for lacewings. The index was
 calculated for lacewings, but should also be relevant for ladybeetles,
 given the similarity of the pollen diet of these two important aphid
 enemies (Bertrand et al. 2019). <strong>For references and
 additional details, see the original article in Journal of Applied
 Ecology.</strong>