Pan trap and plant-flower visitor observation data for: Multi-species crop mixtures increase insect biodiversity in an intercropping experiment

Recent biodiversity declines require action across sectors such as agriculture. The situation is particularly acute for arthropods, a species-rich taxon providing important ecosystem services. To counteract negative consequences of agricultural intensification, creating a less hostile agricultural “matrix” through growing crop mixtures can reduce harm for arthropods without yield losses.
While grassland biodiversity experiments showed positive plant biodiversity effects on arthropods, experiments manipulating crop diversity and agrochemical input use to study arthropods are lacking.
Here, we experimentally manipulated crop diversity (1–3 species, fallows), crop species (wheat, faba bean, linseed, oilseed rape) and agrochemical input (high vs. low) and studied responses of arthropod biodiversity. We tested if arthropod responses were affected by crop diversity, mixtures and management. Additionally, we measured crop biomass.
Crop biomass increased with crop diversity under high-input mangement, while under low management intensity, biomass was highest in two-species mixtures.
Increasing crop diversity positively affected arthropod abundance and diversity, both under low- and high-input management. Crop mixtures containing faba bean, linseed or oilseed rape had particularly high arthropod diversity.
Mass-flowering crops attracted more arthropods than legumes or cereals. Integrating intercropping into agricultural systems could increase flower visits by insects up to 15 million per hectare, thus likely also supporting pollination and pest-control ecosystem services.
Flower-visitor network complexity increased in mixtures containing linseed and faba bean, and under low-input management.
Intercropping can counteract insect declines in farmland by creating beneficial matrix habitat without compromising crop yield.

Methods
The study was conducted as part of an intercropping trial near Münster, Germany, in 2019.

Flower visitor observations: observations were carried out on monocultures of wheat, bean, linseed and their 2- and 3-species mixtures:  Ty(wheat), Fu(faba bean), Bi(linseed), TyFu, TyBi, FuBi, TyFuBi and no crop.

Ty = Wheat variety "Tybalt"; Fu = Bean variety "Fuego"; Bi = Linseed variety "Bingo".= 8 crop mixtures x 2 treatments (high and low) x 4 replicates = 64 plots in total.

on 02.07.2019 (Block 1), 
on 03.07.2019 (Block 2), 
on 03.+04.07.2019 (Block 3),
on 09.+10.07.2019 (Block 4),
AND on 10.07.2019 (Block 1 second time)

1 m² of each plot was observed for 15 min, all contacts with floral organs were counted as one visit flower cover and number of flowering plants per plant species were recorded as well. Pollinators were identified as thoroughly as possible, if species identification was not possible, the higher level was used (family or order)

Pan traps: yellow pan traps were placed at 4 time points on plots containing the following crop mixtures: Ty (wheat), Fu (faba bean), Bi (linseed), Ca (oilseed rape), TyFu, TyBi, TyCa, FuBi, FuCa, BiCa, TyFuBi, TyFuCa, nc (NoCrop).

Ty = Wheat variety "Tybalt"; Fu = Bean variety "Fuego"; Bi = Linseed variety "Bingo"; Ca, Oilseed Rape Variety "Campino" = 13 crop mixtures x 2 treatments (high and low) x 4 replicates = 104 traps per round.

round 1: 28.06.–01.07.2019
round 2: 05.07.–08.07.2019
round 3: 12.07.–15.07.2019
round 4: 23.07.–26.07.2019

Round 3 could not be used, because heavy rainfall flooded the trap.