The Association Between Soil Sampling and Bait Traps in Wireworm Monitoring: A Methodological and Statistical...

The key to implementing IPM of wireworms effectively is to associate feasible, reliable and affordable sampling methods with well-defined damage thresholds. As wireworms live underground, they cannot be observed directly, thus estimating population levels can be challenging. Soil sampling to ascertain larval density is very time-consuming, and although the use of bait traps is much more time-effective, it is unclear how wireworm numbers in bait traps are associated with wireworm density. The work described herein was conducted between 1993 and 1999 in two regions of Northern Italy: Veneto and Piedmont. The experimental protocol involved placing soil bait traps in a 15-30 m × 10 m grid in selected cultivated fields and taking a soil sample 3 m from the location of each bait trap. The number of monitoring points ranged from 12 to 48 per site. Both trap contents and soil cores were put in funnels to dry out, forcing the wireworms to move and fall into a vial, according to the Berlese method. A moderate association was found between the number of wireworms (Agriotes brevis, A. sordidus and A. ustulatus) caught by the bait traps and by soil sampling, indicating a potential for reciprocal estimation between methods. In other words, the number of bait-trap catches can be estimated by soil sampling (e.g., when bait traps cannot be used due to low temperatures or when growing plants cover a field) and vice versa. The potential of bait traps for catching wireworms was shown to be 5 to 25 times higher than the potential of soil sampling. The threshold values for soil samples, which were derived from the original bait-trap values, range between 15 and 20 larvae/m².