J Pest Sci DOI 10.1007/s10340-014-0583-5 ORIGINAL PAPER IPM thresholds for Agriotes wireworm species in maize in Southern Europe Lorenzo Furlan Received: 3 November 2013 / Accepted: 16 March 2014 Ó The Author(s) 2014. This article is published with open access at Springerlink.com Abstract Currently, integrated pest management (IPM) Keywords Wireworms Á A. brevis Á A. sordidus Á of wireworms is not widespread in Europe. Therefore, to A. ustulatus Á IPM Á Bait traps estimate the densities of three major wireworm species in southern Europe (Agriotes brevis Candeze, A. sordidus Il- liger, and A. ustulatus Scha¨ller), bait traps were deployed Introduction pre-seeding in maize fields in north-eastern Italy between 1993 and 2011. Research discovered that there was a sig- EU Directive 2009/128/EC on the sustainable use of pes- nificant correlation between all three wireworm species ticides makes it compulsory to implement integrated pest caught in the bait traps and damage to maize plants, but management (IPM) for annual crops in Europe from Jan- damage symptoms varied. Wherever A. ustulatus was the uary 2014. IPM strategies have not played a significant role main species caught, there was no significant damage to in these crops to date, yet they have been widely used for maize plants, but seeds were damaged. Most of the crops such as orchards and vineyards. Therefore, accurate symptoms caused by A. brevis and A. sordidus were to the information about IPM strategies for annual crops is nee- central leaf/leaves, which wilted because of feeding on the ded urgently, but this information must take into account collar. A. brevis was the most harmful species; when more that arable farming has few resources in terms of income, than one A. brevis wireworm was caught per trap, plant labour and technology. Since the use of soil insecticides is damage sometimes resulted in reduced yield. Five A. widespread, this paper intends to provide reliable IPM ustulatus larvae per trap caused the same damage to maize information to tackle wireworms, the main soil pest in as one A. brevis. A. sordidus came second (threshold two Europe (Furlan 2005). It has proved difficult to implement larvae/trap). These thresholds are reliable for: (1) bare soil IPM strategies for wireworms in Europe due to a shortage in which there are no alternative food sources; (2) average of reliable information on how to assess population levels soil temperature 10 cm beneath the surface of above 8 °C and the relative thresholds (Furlan 2005). Wireworms are for 10 days; (3) soil humidity near to field water capacity, the larvae of click beetles (Coleoptera: Elateridae), but but days of flooding have not been considered. The damage-causing genera and species vary with geographic implementation of the practical method described herein location (Furlan et al. 2000, 2001b, 2007a; Rusek 1972; may lead to effective IPM of wireworms in maize and to a Staudacher et al. 2013). In Europe, most larvae in agri- significant reduction in the number of fields treated with cultural land belong to the Agriotes genus, but the specific soil insecticides. species must be established if we are to predict the potential damage to crops. For example, high populations of Agriotes ustulatus do not damage maize late in the Communicated by M. Traugott. spring (late May–June) because most of the larvae are in a non-feeding phase (Furlan 1998); in the same period, & L. Furlan ( ) however, Agriotes sordidus or A. brevis can seriously Veneto Agricoltura, Agripolis, via dell’Universita` 14, Legnaro, PD, Italy reduce the stand of maize crops (Furlan 2004). The adults e-mail: [email protected] (click beetles) of these species can be divided into two 123 J Pest Sci main groups: (i) adults that do not overwinter and lay eggs accordance with official USDA methods. Soil pH was basic a few days after swarming (A. ustulatus Scha¨ller and A. for all the fields and ranged between 7.9 and 8.3. litigiosus Rossi); and (ii) adults that overwinter, live for months, and lay eggs for a long period after adult hard- Agronomic practices ening (A. sordidus Illiger, A. brevis Candeze, A. lineatus L., A. sputator L., A. obscurus L., A. rufipalpis Brulle`, and A. Conventional agronomic practices were applied to all of the proximus Schwarz) (Furlan 2005). The life cycle of the fields studied (i.e. ploughing, harrowing, fertilization with species in both groups is about 24–36 months. In spring, 240–300 N kg, 70,000–76,000 seeds/ha, interrow width the larvae of group (i) entering the bait traps come from 75 cm, pre-emergence plus post-emergence herbicide eggs laid two years before, but group (ii) larvae come treatments causing very low weed densities, and planting mainly from eggs laid the previous year. Unfortunately, the date from late March to late April). The following com- vast majority of literature on this matter does not report mercial hybrids were used: ANITA, COSTANZA, ALICIA, which species were involved (Hinkin 1976; Chabert and SENEGAL (1993–2001); TEVERE (2002–2004); Blot 1992). Therefore, this present research assesses the DKC6530 (2005–2006); DKC 6530, MITIC, KERMESS, effect of various Agriotes species on maize and looks at KLAXON (2007–2008); DKC6666, NK FAMOSO, thresholds based on wireworms caught in bait traps in order PR31A34, PR32G44 (2009–2010); and DKC6677, to establish a range of IPM strategies. The ultimate aim of PR32G44 and NK FAMOSO (2011). the research is to provide practical information so that European farmers can implement reliable, feasible and Estimation of wireworm population level affordable IPM strategies to prevent wireworms damaging their maize. Bait traps made and used in accordance with Chabert and Blot (1992) were deployed to estimate wireworm popula- tion densities from late February to mid April. These and Materials and methods similar traps were found to be efficient at capturing wire- worms after research in UK conditions (Parker 1994, Field sites 1996). Each trap comprised a plastic pot 10 cm in diameter with holes in the bottom. The pots were filled with ver- Research was conducted in north-east Italy (area covered: miculite, 30 ml of wheat seeds and 30 ml of maize seeds; 45.64N, 12.96E and 45.05N 11.88E) from 1993 to 2011 they were then moistened before being placed into the soil (19 consecutive years) on fields with the following char- 4–5 cm below the soil surface, after which they were acteristics: (1) soil at field water capacity, i.e. no more covered with an 18-cm diameter plastic lid placed 1–2 cm water can be stably retained; after winter, all of the fields above the pot rim. Traps were hand-sorted after 10 days studied, and particularly the bare ones, i.e. no crops con- when the average temperature 10 cm beneath the surface suming water, are usually very humid due to rainfall, was above 8 °C (Furlan 1998, 2004) to ensure that the bait negligible evaporation and transpiration. Sometimes strong traps stayed in the soil for an equal period of wireworm winds dried up the soil, but only the top-most layer and not activity. Agriotes larvae do not feed, or feed very little, at where the traps were placed. Therefore, the soil layer lower temperatures. Generally, the traps were removed containing the traps was always at field water capacity; (2) from the fields 2 to 8 days before maize seeding. No bare soil (no plants growing), since traps perform reliably considerable differences in wireworm feeding activity were when they do not have to compete with plants whose roots observed between 8 and 13 °C, which is the usual tem- produce carbon dioxide, which attracts larvae (Doane et al. perature range in early spring in northern Italy (Furlan 1975); (3) several previous crops had been sown, such as 1998, 2004). Previous investigations (unpublished data) maize, soybean, winter cereals and meadow (e.g. alfalfa, found that only a negligible number of larvae escaped from festuca); meadow must be ploughed at least three months the traps since it was noted that numbers tended to increase before the bait traps are placed in order to make sure that as days passed (Furlan personal observation). The final all ploughed-up meadow plants have died (it was observed number of larvae was assessed under the aforementioned that this takes about three months); the main reason for this conditions, regardless of larvae behaviour on individual procedure is that it allows the bait traps to attract wire- days. Population levels were calculated only on days when worms without the competition of plants, as described humidity was close to field water capacity. Dry top-soil above. Each year, monitoring was conducted in fields forces larvae to burrow deep beneath the surface, away representing a balanced sample of agronomic conditions in from the bait traps (Furlan 1998), and high humidity north-east Italy. Part of the soils was classified with the (flooding in extreme cases) prevents larvae activity since USDA soil texture triangle based on analyses carried out in all the soil pores are full of water and contain no oxygen. 123 J Pest Sci Therefore, any days on which these conditions occurred were counted; the plots covered an area of were excluded from calculations, regardless of the soil 15–18 m 9 1.5 m. The location and the number of the sub- temperature. This obviously resulted in traps sometimes plots were the same in both the untreated/treated strips and being kept in the soil for longer than 10 days. In the UK, completely untreated field. In order to assess wireworm Parker (1994) caught large numbers of Agriotes wireworms damage on emerged plants, plants with typical symptoms in average soil temperatures that ranged from 5 to 10 °C.