DOI: 10.5061/dryad.1zcrjdfqv
title: Data from: Flower fields and pesticide use interactively shape pollen beetle infestation and parasitism in oilseed rape fields.

description: MANUSCRIPT STILL UNDER REVISION Pollen beetles (Brassicogethes spp.) are
 the main pest of oilseed rape (OSR, Brassica napus) in Europe and
 responsible for massive yield losses. Upcoming pesticide resistances
 highlight the need for other means of crop protection, such as natural
 pest control. Sown flower fields aim to counteract the decrease of insect
 biodiversity in agricultural landscapes by providing breeding and foraging
 sites to ecosystem service providers such as parasitoids. However, the
 optimal age and size of flower fields to increase natural pest control is
 still unclear. We conducted experiments on 31 OSR fields located along a
 gradient of landscape-scale semi-natural habitat (SNH). OSR fields were
 located adjacent to flower fields which differed in age, continuity and
 size, or adjacent to crop fields or calcareous grasslands. In the OSR
 fields, pesticide free areas were established to examine interactive
 effects of pesticide use and flower field characteristics. The abundance
 of pollen beetle adults and larvae, parasitism and superparasitism rates
 in OSR were recorded at increasing distances to the adjacent fields. OSR
 next to flower fields maintained continuously for at least 6 years had the
 lowest numbers of pollen beetle larvae. Flower fields and calcareous
 grasslands increased pollen beetle parasitism in adjacent OSR fields
 compared to OSR fields neighbouring crop fields. However, the threshold
 for effective natural pest control of approximately 35% could only be
 reached in the pesticide free areas of OSR fields adjacent to calcareous
 grassland and continuous flower fields. In pesticide-sprayed areas, pollen
 beetle parasitism and superparasitism declined with increasing distance to
 the adjacent field, but they remained on the same level in areas without
 pesticides. Large flower fields (&gt;1.5ha) increased parasitism and
 superparasitism more than small ones. Synthesis and applications: In
 general, older continuous flower fields decrease infestation with pollen
 beetle larvae and enhance parasitism rates in OSR. Furthermore, only
 flower fields larger than 1.5ha were able to push pollen beetle parasitism
 above the threshold level of 35%. Therefore, to promote natural pest
 control, it would be beneficial to maintain large flower fields for
 several years unmanaged, to create stable habitats for natural enemies.
 However, pesticide use has negative effects on OSR pollen beetle
 parasitism and can abrogate positive effects of flower fields on natural
 pest control. This study highlights that sown flower fields have the
 potential to increase natural pest control in OSR, but this potential is
 depending on its age and size and can be hindered by pesticide use.
description: 1) pollen_beetle_larvae_parasitism:
 code_field: Code for the respective experimental oilseed rape
 (OSR) field. Adjacent sites: N: New flower field; R: Refreshed flower
 field; C: Continuous flower field; CG: Calcareous grassland; CC:
 Conventional crop field. L: large (&gt;1.5 ha); S: small
 (&lt;1.5ha). code_plot: Code for the respective
 plot in the experimental oilseed rape (OSR) field. Plots are associated
 with a specific distance to the experimental field edge. This distance is
 displayed in the landscape_field_characteristics data set.
 OSR_plant: Number of the oilseed rape plant (OSR). 3 plants were
 selected per plot and treatment. pesticide_treatment:
 p: pesticide sprayed area; pf: pesticide free area.
 number_open_flowers: The total number of open flowers counted on
 one oilseed rape (OSR) plant. number_larvae_3mm: Number
 of oilseed rape (OSR) pollen beetle larvae
 (<i>Brassicogethes</i> sp.) larger than 3mm collected on one
 OSR plant. number_parasitized_larvae: The number of
 parasitized OSR pollen beetle larvae larger than 3mm by the parasitoid
 wasp <i>Tersilochus heterocerus</i>.
 number_superparasitism: The number of parasitized OSR pollen
 beetle larvae larger than 3mm with more than 1 egg from
 <i>Tersilochus hetercerus</i>.  
 2) pollen_beetle_adults: code_field: Code for
 the respective experimental oilseed rape (OSR) field. Adjacent sites: N:
 New flower field; R: Refreshed flower field; C: Continuous flower field;
 CG: Calcareous grassland; CC: Conventional crop field. L: large
 (&gt;1.5 ha); S: small (&lt;1.5ha).
 pesticide_treatment: p: pesticide sprayed area; pf: pesticide
 free area. plot: Plot in the experimental oilseed rape
 (OSR) field. Plots are associated with a specific distance to the
 experimental field edge. This distance is displayed in the
 landscape_field_characteristics data set. OSR_plant:
 Number of the oilseed rape plant (OSR). 3 plants were selected per plot
 and treatment. number_adult_beetles: The number of
 adult pollen beetles (<i>Brassicogethes </i>sp.) found on the
 main raceme of the oilseed rape (OSR) plants.
   3)
 landscape_field_characteristics: code_field: code for
 the respective experimental oilseed rape (OSR) field. Adjacent sites: N:
 New flower field; R: Refreshed flower field; C: Continuous flower field;
 CG: Calcareous grassland; CC: Conventional crop field. L: large
 (&gt;1.5 ha); S: small (&lt;1.5ha). plot: Plot
 in the experimental oilseed rape (OSR) field.
 distance_field_edge: distance of the experimental plot to the
 respective OSR field edge. size_adjacent_site: size of
 the adjacent site (New flower field; Refreshed flower field; Continuous
 flower field; Calcareous grassland; Conventional crop field) in
 hectare. size_OSR_field: size of the experimental
 oilseed rape (OSR) fields in hectare. SNH_amount:
 Amount of total SNH in the landscape in 1km radius around the focus
 fields.