The Association Between Soil Sampling and Bait Traps in Wireworm Monitoring

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, they are unable to ascertain 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 x 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 18 to 48. Both trap contents and soil cores were put in the trap funnels to dry out, forcing the wireworms to move and fall into a vial, according to the Bernese method. Data were processed with a variety of statistical approaches. 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, bait-trap catch values can be estimated from soil sampling (e.g. when bait traps could not be used due to low temperatures or growing plants covering the 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 estimated soil-sampling thresholds range from 15 to 20 larvae/m².