DOI: 10.5061/dryad.547d7wm9f
title: Flying insect biomass is negatively associated with urban cover in surrounding landscapes

description: Aim In this study, we assessed the importance of local to landscape-scale
 effects of land cover and land use on flying insect biomass. Our main
 prediction was that insect biomass would be lower within more intensely
 used land, especially in urban areas and farmland. Location Denmark and
 parts of Germany. Methods We used rooftop-mounted car nets in a citizen
 science project (‘InsectMobile’) to allow for large-scale geographic
 sampling of flying insects. Citizen scientists sampled insects along 278
 five km routes in urban, farmland and semi-natural (grassland, wetland and
 forest) landscapes in the summer of 2018. The bulk insect samples were
 dried overnight to obtain the sample dry weight/biomass. We extracted
 proportional land use variables in buffers between 50 and 1000 m along the
 routes and compiled them into land cover categories to examine the effect
 of each land cover, and specific land use types, on insect biomass.
 Results We found a negative association between urban cover and insect
 biomass at a landscape-scale (1000 m buffer) in both countries. In
 Denmark, we also found positive effects of all semi-natural land cover
 types, i.e. protected grassland (largest at the landscape-scale, 1000 m)
 and forests (largest at intermediate scales, 250 m). Protected grassland
 cover had a more positive effect on insect biomass than forest cover. The
 positive association between insect biomass and farmland was not clearly
 modified by any variable associated with farmland use intensity. The
 negative association between insect biomass and urban land cover appeared
 to be lessened by increased urban green space. Main conclusions Our
 results show that land cover has an impact on flying insect biomass with
 the magnitude of this effect varying across spatial scales. However, the
 vast expanse of grey space in urbanised areas has a direct negative impact
 on flying insect biomass across all spatial scales examined.
description: Route design and flying
 insect sampling Sampling was carried out along 211 routes from 1
 - 30 June 2018 in Denmark, and along 67 routes between 25 June - 8 July
 2018 in Germany. Across both countries, routes were created across five
 land cover types: farmland, grassland, wetland, forest and urban areas. No
 route could be designed to fit 100% to one land cover type, but each route
 was designed to target a specific land cover type. Each sampling event was
 either driven in one direction for 10 km or 5 km driven back and forth, to
 cover as much of the targeted land cover type as possible. The routes were
 constructed in ArcGIS and QGIS using information from Google Earth, Google
 Maps, OpenStreetMap (OSM), including data from Danish authorities on land
 cover types in Denmark, and also using the German ATKIS data (Amtliches
 Topographisch-Kartographisches Informationssystem) in Germany. Based on
 the target land cover, in Denmark, 64 urban, 59 farmland, 63 grassland, 62
 wetland and 66 forest routes were designed. In Germany, 12 urban, 15
 farmland, 12 grassland, 17 wetland and 14 forest routes were created.
 Sampling of each route was carried out once
 during two time intervals on the same the day: between 12-15 h (midday)
 and again between 17-20 h (evening) with a maximum speed of 50 km/h and
 weather conditions of at least 15°C, an average wind speed of maximum 6
 m/s and no rain. Insects were collected in individual sampling bags that
 were placed in 96% pure ethanol and stored in double-sealed plastic bags
 before the citizen scientists sent the samples back to the research
 institutions.  Flying insect biomass
 Insects were removed from the
 sampling bag with a squeeze bottle containing 96% EtOH and forceps. Empty
 15 or 50 ml centrifuge tubes were weighed, and the insects were
 transferred to the tubes. The insects were dried overnight at 50 ̊C in an
 oven (&gt;18hrs), and the tubes containing the dry insects were
 weighed (Mettler Toledo ME303 in Denmark, Quintix® Precision Balance 310 g
 x 1 mg in Germany) to obtain sample biomass (in total
 mg).  Environmental variables
 We extracted land use
 predictors for insect biomass from four buffer zones for each route: 50 m,
 250 m, 500 m, and 1000 m in five categories; urban, farmland, grassland,
 wetland, and forest. The buffers were calculated as linear buffers around
 each route. Land use intensity data for Denmark were extracted for
 farmland and urban routes. Other variables 
 We extracted potential car
 stop variables to account for sampling heterogeneity. We obtained the
 number of traffic lights or stops of any type (e.g. roundabouts,
 pedestrian crossings, stop signs, railroad crossings) within a 25-30 m
 buffer using OSM. For Danish routes, we obtained the number of roundabouts
 using data from the Danish Map Supply provided by SDFE (Agency for Data
 Supply and Efficiency) (GeoDenmark-data), since data on roundabouts in
 Denmark was limited to three records in OSM. Mean hourly temperature and
 wind was extracted for each route including date and time band from the
 nearest weather station using the rdwd R package for German routes. For
 Danish routes, temperature (within increments from 15-20, 20-25 and 25-30
 ℃), average wind speed (within increments from
 light Breeze 1.6-3.3, gentle breeze: 3.4-5.5, and moderate breeze 5.5-7.9
 metre/second), and sampling time (hh:mm) were registered by the citizen
 scientists.
description: Analyses must be run separately for each country.