Data from: Declining abundance of beetles, moths and caddisflies in the Netherlands

Data used in Hallmann CA, Zeegers T, van Klink R, Vermeulen R, van Wielink P, Spijkers H, van Deijk J, van Steenis W, Jongejans E (2020) Declining abundance of beetles, moths and caddisflies in the Netherlands. Insect Conserv Divers 13:127-139

Data were collected at two groups of sites: De Kaaistoep and Wijster, both in the Netherlands. In addition, we obtained data from two KNMI weather stations (for De Kaaistoep data: weather station Gilze-Rijen, for Wijster data: weather station Eelde, at, respectively, 3.6 and 40 km from trapping locations), from which we extracted relevant parameters.

Collecting at light in De Kaaistoep

De Kaaistoep is a 330 ha managed natural area consisting of heathland, pine forest and grassland. It was established in 1994 on former arable land. Information about the location and management history can be found in the study by Felix and van Wielink (2008). Insects were attracted by light in combination with a white cloth (Supporting Information Fig. S1) over a period of 3.3 h per trapping night, normally starting around sunset (Hallmann et al. 2020). During this sampling period, individuals of the various insect taxa were counted, or were estimated in the case of large numbers. All macro-moths were always counted and identified, while for other groups of insects, between 25 and 100% were collected for identification. Further details of the sampling protocol are given in the study by van Wielink and Spijkers (2013). The data archived her have been collected during 628 trapping nights between 1997 and 2017, on average 30 evenings per year (10–77). Data were available for the period of 1997–2017 for macro-moths (Lepidoptera), beetles (Coleoptera) and ground beetles (Carabidae), while for caddisflies (Trichoptera), lacewings (Neuroptera), true bugs (Hemiptera-Heteroptera and Hemiptera-Auchenorrhyncha) and mayflies (Ephemeroptera) data were available only for the years 2006 and 2009–2017. Of the large number of Coleoptera, only ground beetles, ladybirds and carrion beetles were identified to species up to 2017, accounting for 48 000 of 239 000 beetle specimens.

                  As it is known that the environmental conditions (like temperature) during each trapping night influenced the number of insects caught, we aimed to include relevant covariates in our analyses. Information about the timing and duration of sampling were available for 91.2% of the nights (n = 574), and lacking more in the first few years of sampling than later on. The number of sampling hours per night varied little among years but did increase from an average of 3.1 h (1997–2009) to an average of 3.8 h per night after 2010 (Hallmann et al. 2020). Timing of onset of sampling was roughly at sunset throughout the years, with the exception of the first few years in which sampling started on average up to half an hour after sunset (Hallmann et al. 2020). 

Pitfall traps near Wijster

A long-term monitoring program using pitfall traps was started at the Wijster Biological Station (and continued by the Foundation Willem Beijerink Biological Station) in two nature reserves in the province of Drenthe: National Park Dwingelderveld and the fragmented, but increasingly reconnected Hullenzand. In these reserves restoration measures, mainly in the form of topsoil removal and reconnection, were carried out during the early 1990s. The pitfall data have been collected between 1959 and 2016 at in total 48 unique locations (mean = 9, range 4–19 operating locations per year). The locations consisted mainly of heathlands, with some forest sites, a forest edge and an abandoned crop field. At each location, three square pitfall traps (25 by 25 cm) were installed: one lethal funnel trap with a 3% formaldehyde solution and two live traps. The traps at each location were spaced 10 m apart. Caught ground beetles (Coleoptera: Carabidae) have been identified at weekly intervals. Further details on the sampling protocol and the area are given in the study by den Boer and van Dijk (1994). Because we are only interested in recent trends in insect abundances, and because sampling protocols were not consistent in the early years, we here only archive data collected since 1986. We document two types of data: i) the annual sums per species and location for the period of 1986–2016, and ii) the weekly sums per species and location that have been fully digitised and checked: 2002–2017. 

Annual totals 1986–2016. In total, 7778 records of species-specific counts are archived, which amounted to 264 986 individual ground beetles. For 20 records, we used multiple imputation (Onkelinx et al. 2017) to derive more reliable estimates for suspected erroneous counts. This method is based on the correlation structure between years and between other species. Note that in the years 1998–2001, no monitoring took place, and 2004 was omitted because of incomplete catches. 

Species weights

For biomass estimation we used known species length measurements and known relationships of length to weight (Sabo et al. 2002; García-Barros 2015). For the Carabidae in the Wijster data set, we used the minimum and maximum body length as stated in the Dutch ground beetles field guide (Boeken et al. 2002). 

KaaistoepOrder.csv                

Trich                          = number of Trichoptera individuals

Hemip                       = number of Hemiptera individuals

Neur                          = number of Neuroptera individuals

Ephem                      = number of Ephemeroptera individuals

Hemi.hetero          = number of Hemiptera-Heteroptera individuals

Hemi.cica                = number of Hemiptera- Auchenorrhyncha individuals

T                                 = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

U                                = hourly relative humidity (in %; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

FH                              = hourly average windspeed (in 0.1 m/s)

start                          = date and start time of the measurement

suns.deviate          = number of minutes the measurements started after sunset

tdiff                            = number of hours of measurement

KaaistoepColeo.csv

Coleo                         = number of Coleoptera individuals

T                                 = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

U                                = hourly relative humidity (in %; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

FH                              = hourly average windspeed (in 0.1 m/s)

sunset                       = date and sunset time

suns.deviate          = number of minutes the measurements started after sunset

tdiff                            = number of hours of measurement

KaaistoepLepi.csv

freq                           = number of Lepidoptera individuals

T                                 = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

U                                = hourly relative humidity (in %; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

FH                              = hourly average windspeed (in 0.1 m/s)

sunset                       = date and sunset time

suns.deviate          = number of minutes the measurements started after sunset

tdiff                            = number of hours of measurement

KaaistoepCara.csv

Cara                          = number of Carabidae individuals

T                                 = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

U                                = hourly relative humidity (in %; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

FH                              = hourly average windspeed (in 0.1 m/s)

sunset                       = date and sunset time

suns.deviate          = number of minutes the measurements started after sunset

tdiff                            = number of hours of measurement

species                     = number of individuals of each of 94 Carabidae species

KaaistoepSilphi.csv

Silph                          = number of Silphidae individuals

T                                 = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

U                                = hourly relative humidity (in %; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

FH                              = hourly average windspeed (in 0.1 m/s)

sunset                       = date and sunset time

suns.deviate          = number of minutes the measurements started after sunset

tdiff                            = number of hours of measurement

species                     = number of individuals of each of 6 Silphidae species

KaaistoepCocci.csv

Cocci                          = number of Coccinellidae individuals

T                                 = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

U                                = hourly relative humidity (in %; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

FH                              = hourly average windspeed (in 0.1 m/s)

sunset                       = date and sunset time

suns.deviate          = number of minutes the measurements started after sunset

tdiff                            = number of hours of measurement

species                     = number of individuals of each of 23 Coccinellidae species

KaaistoepMacro2.csv (non-zeros)

freq                           = number of macro-Lepidoptera individuals

name                        = macro-Lepidoptera species

year                          = year of measurement

daynr                        = day of the year

KaaistoepLepiWeights

name                        = macro-Lepidoptera species

mgSabo                   = mass (mg) estimated using Sabo et al. (2002)

mgGarciaBarros   = mass (mg) estimated using García-Barros (2015)

WijsterWeek.csv

freq                           = number of ground beetle individuals

date                           = date of emptying trap

dt                                = number of days a trap has been open

trap                           = randomized trap ID

FG                              = hourly average windspeed (in 0.1 m/s)

TG                              = hourly average temperature (in 0.1 degrees Celsius; at 1.5 meter height)

RH                              = hourly sum of precipitation (in 0.1 mm) (negative values for <0.05mm)

UG                              = hourly relative humidity (in %; at 1.5 meter height)

species                     = number of individuals of each of 134 ground beetle species

WijsterColeoWeights

name                        = ground beetle species

mgSabo                   = mass (mg) estimated using Sabo et al. (2002)

References

Boeken M, Desender K, Drost B, van Gijzen T, Koese B, Muilwijk J, Turin H, Vermeulen R (2002) De Loopkevers van Nederland en Vlaanderen (Coleoptera, Carabidae). Jeugdbondsuitgeverij, Nederland

den Boer PJ, van Dijk TS (1994) Carabid Beetles in a Changing Environment. 94‐6, Wageningen Agricultural University

Felix R, van Wielink P (2008) On the biology of Calodromius bifasciatus and related species in De Kaaistoep (Coleoptera: Carabidae). Entomol Berichten 68:198–209

García-Barros E (2015) Multivariate indices as estimates of dry body weight for comparative study of body size in Lepidoptera. Nota Lepidopterol, 38:59–74

Hallmann CA, Zeegers T, van Klink R, Vermeulen R, van Wielink P, Spijkers H, van Deijk J, van Steenis W, Jongejans E (2020) Declining abundance of beetles, moths and caddisflies in the Netherlands. Insect Conserv Divers 13:127-139

Onkelinx T, Devos K, Quataert P (2017) Working with population totals in the presence of missing data comparing imputation methods in terms of bias and precision. J Ornithol 158:603–615

Sabo JL, Bastow JL, Power ME (2002) Length–mass relationships for adult aquatic and terrestrial invertebrates in a California watershed. J North Am Benthol Soc 21:336–343

van Wielink P, Spijkers H (2013) Insects nightly attracted to light at a single site in De Kaaistoep, The Netherlands. Orders, families and species identified in 1995–2011. Entomol Berichten, 73:200–214