DOI: 10.5061/dryad.d51c5b0b2
title: Data from: Linking landscape structure, floral resource distribution, pollen use, and movement distances of a generalist predator

description: Understanding the habitat use and movement patterns of natural enemies in
 agricultural landscapes is essential for enhancing biological pest
 control. Since many natural enemies rely on floral resources, the
 distribution of these resources in combination with movement behaviour
 likely influence biological control in field crops. Nevertheless, few
 studies have assessed natural enemy movement at the landscape scale. Here
 we estimated minimal movement distances of the green lacewing Chrysoperla
 carnea based on consumed pollen and the spatial distribution of the
 respective plant species in 24 agricultural landscapes (500 m radius).
 Lacewings were sampled using sticky traps in the centre of each landscape,
 and the consumed pollen were identified. The location of the most
 important pollen-providing plants was mapped in each landscape. Distances
 to potential sources of pollen consumed by 346 lacewings were used to
 derive minimal movement distances. Lacewings consumed mostly pollen from
 insect-pollinated plants that were present within 500 m from the sampling
 location. The distance to the nearest source of consumed pollen exceeded
 200 m in 31% of lacewing individuals, demonstrating the relevance of the
 landscape scale to understand their population dynamics. Distances were
 shorter to insect-pollinated than to wind-pollinated plants, and shorter
 early than late in the season. Mean and median distances to pollen sources
 were negatively associated to flower availability and edge density in the
 landscape, but this was not the case for minimal distances. Synthesis and
 applications: Our findings suggest that the spatial distribution of
 flowering wild plants can inform movement patterns of lacewings and other
 flower-visiting insects in agricultural landscapes. In addition, the
 location of floral resources in the landscape is important for its
 capacity to sustain natural enemies. Given the strong reliance of
 lacewings on pollen from nearby insect pollinated woody plants, the
 promotion of native shrubs and trees, such as Prunus, Salix and Castanea,
 should be prioritised for natural enemy enhancement in agricultural
 landscapes. Doing this in the form of hedgerows or agroforestry systems
 would lead to only minimal reduction in production areas, and provide
 additional benefits such as biodiversity conservation.
description: Lacewing sampling and pollen diet Adult
 lacewings were sampled in 2019 in the Upper Rhine Valley,
 Rhineland-Palatinate, Germany (49.07-49.29°N, 8.09-8.34°E), in 24
 landscapes (radius 0.5 km) that span a gradient of landscape composition
 and configuration and floral resource availability (Fig 1; see Eckerter et
 al., 2020 and Supporting Information for details). Landscape centres were
 at least 800 m apart (average: 1993 ± 183 m). Land-use categories (areas
 of forest, arable land, semi-natural habitats, urban areas) at every
 landscape were mapped in 2019 during insect and plant samplings. Using
 QGIS, measures of landscape composition (proportion of cereals, proportion
 of semi-natural habitats, Shannon Index of landscape and crop diversity)
 and configuration (edge density, calculated as the total length of edges
 between landscape elements divided by the total area of the landscape; and
 mean field size, i.e., average size of arable fields on each landscape)
 were calculated for each landscape (Table S1). In the
 centre of each landscape, two sticky traps were placed at the edge between
 a herbaceous semi-natural habitat and an arable field at 1.5 m height,
 separated by 20 meters. Traps had two collecting surfaces facing South and
 North and each surface had blue, white, and yellow sticky areas (see
 Supporting Information for more details). Traps were active for a total of
 eight weeks from May 1st to July 4th. For further analyses, the sampling
 period was divided into early season (from May 1st to June 4th,
 corresponding to approximately 100 to 200 Growing Degree Days -GDD-) and
 late season (from June 5th to July 4th, equivalent to 200 to 400 GDD).
 This classification was based on a previous study of <em>C.
 carnea</em> pollen diet, which showed a marked compositional shift
 between these phases (Bertrand et al., 2019). Each landscape was visited
 every two weeks and all the collected lacewings were removed from the
 traps using brushes with white spirit and tweezers. Each individual was
 stored in a separate Eppendorf tube with 70% ethanol. In the laboratory,
 all the lacewings belonging to the genus <em>Chrysoperla</em>
 were identified to the species level using morphological features when
 possible (San Martin, 2004; personal communication with P.
 Duelli). The consumed pollen by lacewings (i.e., pollen
 grains in the gut) were retrieved using acetolysis following the steps of
 Jones (2012, 2014). During this procedure, insect tissues and all pollen
 material with the exception of the outer pollen wall, are removed
 (Southworth 1974), yielding clean pollen exines for identification. The
 method was previously used to study the pollen diet of lacewings and
 ladybeetles (Alcalá Herrera et al., 2021; Bertrand et al., 2019; Villenave
 et al., 2006). In short, external pollen on the bodies of lacewings were
 removed by rinsing them in ethanol. Each individual was placed in a
 centrifuge tube for acetolysis. After centrifugation, pollen pellets were
 diluted in 50% (v/v) glycerin and put on slides for pollen identification
 (Supporting Information). Pollen grains were identified using
 palynological keys (Beug, 2004), a photo atlas (Reille, 1992), and
 reference collections of the Ecosystem Analysis Group (University
 Kaiserslautern-Landau). Pollen were usually identified to plant species
 level, but for some cases to lower taxonomic levels. We further refer to
 “pollen records” to describe all the different pollen types identified
 across all collected lacewings. Floral resource
 mapping The major floral pollen resources for lacewings
 were assessed during two different sampling rounds (see Supporting
 Information for details). First, the cover (in m<sup>2</sup>)
 of all woody plants was mapped in 2017-2018 in sampling plots of 10 x 10 m
 in all hedgerows and forest edges (first ten meters) of each landscape
 (orange dots in Fig. 1D; Eckerter et al., 2020). The forest interior was
 not mapped since <em>C. carnea</em> is mostly active in open
 farmland during spring and summer (Duelli et al., 2002). The cover of each
 tree was estimated by measuring its crown projection area on the ground.
 Second, the cover (in m<sup>2</sup>) of herbaceous flowering
 plants was mapped in 2019 within each landscape element containing
 herbaceous flowering plants. In grassy field margins, hedgerows, and
 forest edges, the total cover of herbaceous flowering plants was recorded
 (red lines in Fig. 1D). In meadows and crops, the cover of flowering
 plants was upscaled from ten 1 m<sup>2</sup>-subplots to the
 total meadow and crop area (green and yellow polygons in Fig. 1D,
 respectively). Mapped plants were identified at species level using
 vegetation keys (Parolly et al., 2006; Schauer et al., 2012; Schulz,
 2014). For herbaceous plants, only species that represented &gt;5% of
 the pollen consumed by <em>C. carnea </em>in a previous study
 in the region (Bertrand et al., 2019) were sampled (Table S2). The
 locations of these flowering plant species were mapped and digitized to
 create floral resource maps in QGIS 3.18.3 (QGIS Development Team, 2021).
 Floral resource area (i.e., area of the landscape covered by plants
 consumed by lacewings), flower diversity (Shannon Index of diversity,
 considering the identity and area of each plant species), and early and
 late Flower Availability Indices (FAI) were calculated with this
 information (see Eckerter et al. 2020 and Supporting Information for
 details). Floral resource distribution and movement
 distance estimation To infer minimal movement distances
 and characterize the floral resource distribution, we measured all
 distances between the location of the sticky trap where a lacewing was
 captured and the locations of plants from which pollen detected in that
 lacewing could originate within that respective landscape using QGIS.
 Since lacewings usually ingested pollen from more than one plant species,
 this procedure was followed for each pollen type. This resulted in a list
 of distances for each pollen type that a specific lacewing individual had
 ingested. From this list, the minimal distance to each pollen source
 (distance to the nearest source of that pollen type, which represents the
 minimal distance a lacewing must have moved after consuming the pollen
 grains), and mean and median distances (average distances to all the
 resources of that type in the landscape, which is a measure for the
 resource distribution in the landscape) were calculated for each lacewing
 using the R package <em>dplyr </em>(Wickham et al., 2015).
 Furthermore, for lacewings that consumed more than one pollen type, we
 selected the plant species that had the highest minimal distance because
 this is the minimal distance that the lacewing individual must have moved.
 These calculations were done separately for insect- and wind-pollinated
 plants, but only data from insect-pollinated plants was used for
 addressing objectives (iii) and (iv), as we expected that these represent
 visits to insect-pollinated plants. For pollen from wind-pollinated
 plants, we cannot exclude that lacewings were taking up the pollen after
 being displaced by wind.
description: # Data from: **Linking landscape structure, floral resource distribution,
 pollen use and movement distances of a generalist predator**
 [https://doi.org/10.5061/dryad.d51c5b0b2](https://doi.org/10.5061/dryad.d51c5b0b2) The raw data set includes the data used for the article at the level of each pollen record (e.g., a pollen type consumed by a lacewing) for each lacewing individual. In the Metadata sheet, a description of all variables included in the Raw data sheet is provided. These variables include metrics of landscape composition (proportion of arable land, proportion of seminatural habitats), landscape configuration (edge density, woody edge density), flower availability (flower area in the landscape, flower diversity in the landscape, early and late Floral Availability Index), Landscape ID (focal landscape were each lacewing was collected), Lacewing ID, species ID, sampling month and season, type of pollen and number of grains counted, vector of pollen (wind or insect), number of potential sources of the pollen in the landscape, and distances between sources and the sticky trap were the lacewing was collected (minimum, mean, and median, in meters).