DOI: 10.5061/dryad.h44j0zpqs
title: Dataset: Floral presence and flower identity alter cereal aphid endosymbiont communities on adjacent crops

description: Floral plantings adjacent to crop fields can recruit populations of
 natural enemies by providing flower nectar and non-crop prey to increase
 natural pest regulation. Observed variation in success rates might be due
 to changes in the unseen community of endosymbionts hosted by many
 herbivorous insects, of which some can confer resistance to natural
 enemies, e.g. parasitoid wasps. Reduced insect control may occur if highly
 protective symbiont combinations increase in frequency via selection
 effects, and this is expected to be stronger in lower diversity systems.
 We used a large-scale field trial to analyse the bacterial endosymbiont
 communities hosted by cereal aphids (Sitobion avenae) collected along
 transects into strip plots of barley plants managed by either conventional
 or integrated (including floral field margins and reduced inputs) methods.
 In addition, we conducted an outdoor pot experiment to analyse
 endosymbionts in S. avenae aphids collected on barley plants that were
 either grown alone or alongside one of three flowering plants, across
 three time points. In the field, aphids hosted up to four symbionts. The
 abundance of aphids and parasitoid wasps was reduced towards the middle of
 all fields while aphid symbiont species richness and diversity decreased
 into the field in conventional, but not integrated, field-strips. The
 proportion of aphids hosting different symbiont combinations varied across
 cropping systems, with distances into the fields, and was correlated with
 parasitoid wasp abundances. In the pot experiment, aphids hosted up to six
 symbionts. Flower presence increased natural enemy abundance and
 diversity, and decreased aphid abundance. The proportion of aphids hosting
 different symbiont combinations varied across the flower treatment and
 time and were correlated with varying abundances of the different
 specialist parasitoid wasp species recruited by different flowers.
 Synthesis and applications. Floral plantings and flower identity had
 community-wide impacts on the combinations of bacterial endosymbionts
 hosted by herbivorous insects, which correlated with natural enemy
 diversity and abundance. We recommend that integrated management practices
 incorporate floral resources within field areas to support a more
 functionally diverse and resilient natural enemy community to mitigate
 selection for symbiont-mediated pest resistance throughout the cropping
 area.
description: Field data were collected from The CSC platform at Balruddery
 Farm near Dundee, Scotland in 2016 and 2017. Conventional and integrated
 management treatments were randomly allocated to each half, and (for the
 barley fields) in each field, half three different barley varieties were
 planted as plot strips. <em>Sitobion avenae</em> aphids were
 collected on 6th July 2016 and 3rd July 2017, at four distances (5, 15,
 30, 50 m) from the edge of the field into each barley variety strip.
 Aphids were stored in 70% ethanol and shipped to Technical University of
 Munich for symbiont analysis. At each sampling location (distance into the
 field strip), a maximum of five aphids (one per colony) were collected
 from three adjacent infested tillers in every barley strip (variety);
 aphids reproduce asexually, and females deposit a group of offspring in
 one patch before moving away, this approach minimises the chance of
 collecting aphids from the same clonal mother. Total aphid number was also
 counted for these three tillers. In total, there were four sampling
 distances for three barley varieties, repeated across the two management
 systems, and across two years. Additional data were collected on % cover
 of the crop and weed plants in the sampled areas using a 1 m2 quadrat to
 estimate the projected area of ground covered by each vegetation type in
 mid-July. Data on parasitoid and generalist natural enemy abundance were
 obtained from two yellow sticky traps, one placed at the top and one at
 the bottom of the plant canopy, at each sampling location, in mid-to-late
 July. Data were collected from an outside pot
 experiment in 2018. We used four barley cultivars and three flowering
 plants (<em>Fagopyrum esculentum, Vicia faba, Trifolium
 pratense)</em>, with flower treatments of no-flower, one flower
 (each for the three species) and mixed flowers. Treatments were replicated
 six times and the experiment set up as a complete randomised block design.
 All insects were allowed to naturally colonise the plants and observations
 were taken weekly (2018) from May until seed harvest in July. Data
 collected included all aphid and natural enemy species per plant. Aphids
 were collected for endosymbiont analysis on 23rd June (late June), 11th
 July (early July) and 25th July (late July). One aphid per colony on every
 plant was collected and stored in 70% ethanol. Data
 were analysed in R using linear models, mixed effect models, and
 structural equation models. 
description: The Excel file contains an explanation of each of the variables
 and the two datasets in three worksheets: (1) ReadME
 with variable explanations (2)
 DATA_PotExperiment (3) DATA_FIeldExperiment