Carabidae - Effect of the trapping liquid

Description

Methods (English)

The experiment was conducted on 20 commercial agricultural plots located in the loamy and Condruzian regions of Belgium (Figure 1). The region is characterised by a temperate oceanic climate, with average annual precipitation of 800 mm and an average annual temperature of 10°C. All the farms included in the study practise conventional farming and follow a crop rotation that includes the "beetroot – winter cereals" sequence, which is widespread in the region. Conventional farming in this context refers to a production system that employs chemical inputs (synthetic fertilisers and pesticides) and mechanised methods to maximise yields, while also allowing the adoption of practices such as reduced tillage or decreased pesticide use, without compromising the farm's conventional status.

This experimental design allows for the comparison of vinegar’s effectiveness with that of more conventional liquids in terms of carabid capture, taking into account seasonal variations and the cultivation conditions of two contrasting crops: beetroot and winter cereals.

In 2023, trapping campaigns were conducted on beetroot plots during three periods, each lasting three weeks. Each period included three sampling events, with each trap being replaced after one week and repeated twice. This design compared vinegar to propylene glycol using 1080 traps distributed across 20 plots. The first period, “Post-Sowing”, occurred from 7 May to 1 June 2023. The second period, “Mid-Crop”, took place from 27 June to 20 July 2023. The third period, “Pre-Harvest”, extended from 8 August to 31 August 2023.

In 2024, trapping campaigns on winter cereal plots were conducted over two three-week periods. Each period again included three sampling events, with each trap being replaced after one week and repeated twice. This second setup compared vinegar to brine using 612 traps distributed across 17 plots. The first period, “Mid-Crop”, was from 1 to 26 April 2024. The second period, “Pre-Harvest”, took place from 10 June to 5 July 2024.

In each plot, six Barber traps were set on the ground to capture terrestrial arthropods. The traps were placed at the centre of the plots to minimise edge effects. The six traps per plot were spaced at least 15 metres apart and arranged according to a constant spatial layout (Figure 2). Each trap consisted of two nested containers (volume: 400 mL; height: 100 mm; upper diameter: 85 mm; lower diameter: 72 mm). The outer container serves as a support and stabilises the inner container, reducing soil disturbance during installation. A funnel, made from the upper part of a plastic bottle, was added to each trap to minimise the escape of captured individuals and to prevent the entry of small unwanted vertebrates. A translucent plastic roof was installed 15 cm above each trap to protect the contents from precipitation. This setup follows the standardised protocols recommended by Brown & Matthews (2016) and Hohbein & Conway (2018). Carabid identification was carried out to species level using identification keys provided by Coulon et al. (2011) and Roger et al. (2012). 

To test the effectiveness of vinegar as a trapping liquid, the Barber traps were compared with traps containing propylene glycol or brine. In 2023, on the 20 beetroot plots, three of the six traps per plot were filled with 200 mL of 7° alcohol vinegar, while the other three were filled with 200 mL of 50% diluted propylene glycol. In 2024, on 17 of these same plots, during the winter cereal cultivation, three traps per plot were filled with 200 mL of 7° alcohol vinegar and the other three with 200 mL of brine (200 g/L).