IPM thresholds for Agriotes wireworm species in maize in Southern Europe

Currently, integrated pest management (IPM) of wireworms is not widespread in Europe. Therefore, to estimate the densities of three major wireworm species in southern Europe (Agriotes brevis Candeze, A. sordidus Illiger, and A. ustulatus Schäller), bait traps were deployed pre-seeding in maize fields in north-eastern Italy between 1993 and 2011. Research discovered that there was a significant correlation between all three wireworm species caught in the bait traps and damage to maize plants, but damage symptoms varied. Wherever A. ustulatus was the main species caught, there was no significant damage to maize plants, but seeds were damaged. Most of the symptoms caused by A. brevis and A. sordidus were to the central leaf/leaves, which wilted because of feeding on the collar. A. brevis was the most harmful species; when more than one A. brevis wireworm was caught per trap, plant damage sometimes resulted in reduced yield. Five A. ustulatus larvae per trap caused the same damage to maize as one A. brevis. A. sordidus came second (threshold two larvae/trap). These thresholds are reliable for: (1) bare soil in which there are no alternative food sources; (2) average soil temperature 10 cm beneath the surface of above 8 °C for 10 days; (3) soil humidity near to field water capacity, but days of flooding have not been considered. The implementation of the practical method described herein may lead to effective IPM of wireworms in maize and to a significant reduction in the number of fields treated with soil insecticides.