Pest abundance and timing of migration relative to the vulnerable crop stage influence the severity of crop damage and yield loss to insect pests in oilseed rape (OSR). Both abundance and timing are influenced by landscape composition, changes therein due to crop rotation, and temperature. The need for sustainable and temperature-adapted management strategies of OSR pests due to the environmental harm of current conventional practices and global warming calls for a better understanding of the combined effects of landscape composition and temperature on pest abundances, larval parasitism, crop damage and yield, but also of the role of crop phenology for crop damage and yield under field conditions. Here, 29 winter OSR crops were studied along a multi-annual mean temperature gradient (MAT, 1981–2010) in Bavaria, Germany. We measured pest abundances (pollen beetles, stem weevils), crop damage (bud loss, stem tunnelling), pollen beetle larval parasitism and crop yield and calculated Julian dates of flowering from biweekly observations of growth stages. Pest abundances and parasitism were analysed with regard to MAT and landscape parameters at six scales (non-crop habitat and OSR area, change in the proportion of OSR area relative to the previous year; 0.6 km, and 1–5 km in 1-km steps), while analysis of crop damage and yield also included Julian date of flowering. Pollen beetle abundance was increased under higher MAT, but less strongly when OSR proportions were high (1-km scale) and not strongly reduced relative to the previous year (5-km scale), while pollen beetle larval parasitism was overall low but exceeded 30% (considered as threshold for effective natural control) occasionally under both low and high MAT. In contrast to abundance of adult pollen beetles, stem weevil larval abundance – as well as stem damage – did not respond to landscape composition nor MAT. Despite high abundance of adult pollen beetles under high MAT, crop yield was high (and the proportion of bud loss low) under high MAT when OSR flowered early. Our results underpin the potential of targeted landscape management (e.g. through regionally coordinated crop rotations) and timing of flowering (e.g. through cultivar choice) for environment-friendly and temperature-adapted pest management in winter OSR.

Winter oilseed rape plants were sampled during flowering and crop ripening on 29 study sites across a spatial multi-annual mean temperature gradient (1981-2010) in Bavaria, Germany. Flowering samples were stored at -20°C and samples taken during crop ripening were dried for yield assessment. We assessed pest abundances (adult pollen beetles, stem weevil larvae), pollen beetle larval parasitism, crop damage (proportion of bud loss and stem tunneling) and seed yield and calculated field-level Julian date of flowering from biweekly growth stage observations. During sampling at flowering, plants were cut at ground-level and were carefully bagged to assure that also adult pollen beetles on the plant were included in the sample. Adult pollen beetles on plants and inside sampling bags were counted. Then, all organs on the main raceme of winter oilseed rape plants were counted distinguishing between ‘lost buds’ (stalks without buds or pods and stalks carrying dead buds), broken stalks (stalk with visibly moist tips at the breakage due to breaking off in the frozen stage of the sample) and all other organs (pods, flowers, flower buds). From there, we calculated the proportion of ‘lost buds’ relative to all organs on the main raceme.  Flowers and flower buds >3mm on the entire plants were scanned for pollen beetle larvae. Larvae > 2mm were counted and presence-absence of black parasitoid eggs inside larvae recorded to calculate the proportion of parasitized pollen beetle larvae. Besides, stem length with diameter >=5mm was measured and then cut open to count the number of stem weevil larvae and to measure the length of orange-brown-coloured pith due to the presence of stem weevil larvae. Proportion of stem damage was calculated as length of stem damage relative to stem length. To obtain seed yield values per plant, number of pods per ripe, air-dried plant were counted as well as the number of seeds per pod for 20 pods, and 400 seeds per plant were weighted. Prior to analysis, exclusion criteria were applied to standardize data (e.g. exclusion of sites for analysis when information available on less than three plants per site). For details we refer to the manuscript.

Fricke et al OSR data processing (.R file)

This R-script contains all code needed to process data in preparation for data analysis, except for data standardization that is included in the R-script on data analysis.

Fricke_et_al_OSR_data_processing.R

Fricke et al OSR data analysis (.R file)

This R-script contains the code used to standardize data (e.g. applying exclusion criteria) and to analyse pest abundance, parasitism, and crop damage and yield data including generalized linear mixed effect models and multimodel averaging.

Fricke_et_al_OSR_data_analysis.R

Fricke et al OSR data processing

Raw data on measures per plant, plant organ and pod as well as biweekly growth stage observations and general site information were processed using the accompanying R-script to obtain proportions of bud loss on the main raceme, proportions of parasitized pollen beetle larvae, proportions of stem damage, seed yield per plant and calculated Julian dates of flowering, and complete data sets for analysis. The resulting processed data were used in the R-script on data analysis.

Fricke_et_al_flowering_sample_data_per_plant_raw.csv

Metadata_Fricke_et_al_flowering_sample_data_per_plant_raw.txt

Fricke_et_al_flowering_sample_data_per_plant_organ_raw.csv

Metadata_Fricke_et_al_flowering_sample_data_per_plant_organ_raw.txt

Fricke_et_al_yield_sample_data_per_plant_raw.csv

Metadata_Fricke_et_al_yield_sample_data_per_plant_raw.txt

Fricke_et_al_yield_sample_data_per_pod_raw.csv

Metadata_Fricke_et_al_yield_sample_data_per_pod_raw.txt

Fricke_et_al_growth_stage_data.csv

Metadata_Fricke_et_al_growth_stage_data.txt

Fricke_et_al_site_info_data.csv

Metadata_Fricke_et_al_site_info_data.txt

Fricke_et_al_flowering_sample_data_processed.csv

Metadata_Fricke_et_al_flowering_sample_data_processed.txt

Fricke_et_al_yield_sample_data_processed.csv

Metadata_Fricke_et_al_yield_sample_data_processed.txt

Fricke et al data on landscape parameters

This dataframe contains the landscape variables 'proportion of non-crop area' (= forest + permanent managed grassland + semi-natural habitats; year: 2019), 'proportion of oilseed rape area' (year: 2019), 'change in oilseed rape area relative to the previous year' (year: 2019 relative to 2018) at multiple spatial scales as used in the accompanying R-script on data analysis.

Fricke_et_al_landscape_data.csv

Metadata_ Fricke_et_al_landscape_data.txt