2.2.2. Larval Monitoring

A considerable amount of work has been done in North America and Europe to assess the potential of replacing time-consuming soil sampling with in-field wireworm bait stations [32]. Due to the sampling effort they require and the non-random distribution of the larvae in fields [30], soil sampling is of little interest [32]. Bait systems utilize the attraction of wireworms by the CO2 given off by respiring seeds [74]. Wireworms probably perceive CO2 via clusters of sensilla on the maxillary and labial palps [75]. This probably accounts for the fact that although a large range of vegetable- and cereal-based baits have been tested, baits based on germinating cereal seeds tend to be the most effective [32,76]. In addition, baits based on germinating cereal seeds put in pots (Figure 3B), proved to be an unbiased, time-saving monitoring tool for *Agriotes* wireworms. Since significantly more larvae are found inside the pot than in the other trap types (i.e., plates and meshbags), this method can be used without the time-consuming evaluation of the surrounding soil cores [77]. This trap design proved to be effective for attracting non-*Agriotes* species (*Aeolus mellillus*, *Limonius californicus*, *L. infuscatus*) as well [78]. The catch potential of pot baits can be augmented by increasing the number of pot holes [79]. Various techniques for improving the efficacy of wireworm bait systems have been tested. These include covering the bait with plastic [80,81] to raise the soil temperature. The trap designed by Chabert and Blot [80], a modified version of the trap described by Kirfman et al. [81],

comprises a 650 mL plastic pot (10 cm in diameter) with holes (the ordinary number of those used for tree nursery) in the bottom. The pots are filled with vermiculite, 30 mL of wheat seeds, and 30 mL of maize seeds; they are then moistened before being placed into the soil 4–5 cm below the soil surface, after which they are covered with an 18 cm diameter plastic lid placed 1–2 cm above the pot rim. These traps have been used long term following a standardized procedure by Furlan [35]: traps were hand-sorted after 10 days when the average temperature 10 cm beneath the surface was above 8 ◦C [9,10] to ensure that the bait traps stayed in the soil for an equal period of wireworm activity. The final number of larvae was assessed under the aforementioned conditions, regardless of larvae behavior on individual days. Population levels should be assessed only when humidity is close to field water capacity. Indeed, dry top-soil forces larvae to burrow deep beneath the surface, away from the bait traps [9], and high humidity (flooding in extreme cases) prevents larval activity since all the soil pores are full of water and contain no oxygen.
