The use of click beetle pheromone traps to optimize the risk assessment of wireworm (Coleoptera: Elateridae) maize damage

Abstract

Maize seeds are routinely coated with insecticide to target Agriotes spp. larvae (wireworms). However, in order to find fields where pest control is actually needed, it might be useful to estimate the adult Agriotes population levels and thus the pressure they exert, with a low-cost risk assessment tool, such as YATLORf (Yf) sex pheromone traps. A database containing 17 consecutive years (1998-2014) of field monitoring was analyzed, with information including both pheromone-trap catches of adults and maize-plant damage by wireworms. Significant associations were discovered between seasonal adult catches in-field, subsequent wireworm populations, and plant damage/yield reduction. When each trap contained over 1,100 A. sordidus adults and over 210 A. brevis adults one year prior (Y-1), the risk of 15%-plus plant damage in Year 0 (Y0) increased by 6 times and 37 times respectively when compared with lower numbers. More than 1,000 A. brevis adults/trap two years prior (Y-2) increased the risk of 15%-plus plant damage in Y0 by 13 times when compared with lower numbers. Cumulative thresholds were also found in Y-1 and Y-2 at the same site. Yf threshold values allowed us to detect fields with a negligible crop-damage risk and thus to reduce the use of insecticides. Insecticides, including high-impact ones, such as neonicotinoids 1 , are used prophylactically worldwide in maize and other annual crops 2. Most farmers apply soil insecticides at planting to combat wireworms (Agriotes spp. larvae), but they do not evaluate whether an economically damaging wireworm population is present 2. This approach is used because farmers are generally unaware of Integrated Pest Management (IPM) strategies, little independent advice is available, and simple low-cost, low time-consuming monitoring tools are unknown to them 3. Easy-to-use, economical, and reliable tools are needed to monitor the main arable crop pests if all farmers in EU Member States are to meet the compulsory objectives of Directive 128/2009/EC. Therefore, the availability of effective low-cost monitoring tools for Europe's main soil pests (Agriotes spp. 4,5) is a key factor for improving the situation and will make it easier to implement IPM in the main arable crops (maize, sunflower and canola). The use of these tools would allow researchers to locate areas and/or fields with pest populations below the economic threshold, as they account for the vast majority of the cultivated land 4,5. One potential tool is the YATLORf trap (Yf) 6,7. Produced by ROSA Micro S.r.l., this effective, non-saturable trap is baited with the pheromone lure of a given species, performs species-selective catches, and can be used to monitor adults of Agriotes species (click beetles) in a specific area. Yf traps have been developed and optimized for all major pest of Agriotes genus in Europe (A. brevis Candeze, A. lineatus L., A. litigiosus Rossi, A. obscurus L., A. rufipalpis Brullé, A. sordidus Illiger, A. sputator L., A. ustulatus Schäller) 6,8,9 , with some of these species being major pests...

Assessment of the Attraction Range of Sex Pheromone Traps to Agriotes (Coleoptera, Elateridae) Male Click Beetles in South-Eastern Europe

“…It therefore appears very promising for future experiments on wireworm population reduction to test the potential of trap grids inoculated with entomopathogen spores based on the maximum sampling range of each species (Table 3), plus sub-multiples or multiples thereof. Successful results would make effective, low-cost wireworm population control tools available, thus providing an alternative to pesticides when IPM procedures have identified a high risk of wireworm damage to arable crops [26].…”

“…The Yf trap's white bottom was placed facing down, with its brown edge 1-2 cm below the soil. We used two lure positions: a low position for A. brevis and A. sordidus, and a high position for A. litigiosus and A. ustulatus, with the lure topside facing down in both cases (Figure 1 [26]). On every inspection, the bottom was cleaned up, with soil and any residuals being removed.…”

“…Adult click beetles (A. brevis, A. litigiosus, A. sordidus, and A. ustulatus) were captured using Yf sex pheromone traps [9,26] from a number of infested fields between the beginning and the peak of their swarming period: late March to April for A. brevis; late April to May for A. sordidus [23]; late May to June for A. litigiosus [18]; early June to mid-July for A. ustulatus [15]. These traps proved to be suitable for catching both flying and crawling species throughout the season.…”

“…YATLORf (Yf) sex pheromone traps have been designed for a range of Agriotes species [9,25]. They have proven to be highly efficient in capturing click beetle (Agriotes) species [9], and a clear relationship was found between male click beetle catches in pheromone traps and subsequent wireworm abundance in the related area for at least three species: A. brevis, A. sordidus and A. ustulatus [26]. This made it possible to predict potential wireworm damage, thus improving integrated pest management (IPM) of wireworms.…”

Species Identification of Wireworms (Agriotes spp.; Coleoptera: Elateridae) of Agricultural Importance in Europe: A New “Horizontal Identification Table”

“…Another important IPM principle establishes that when damage thresholds are exceeded, non-chemical pest control methods should be considered as a replacement for chemical treatment. Setting up non-chemical methods to control wireworms, such as agronomic strategies [20], biocidal plant materials [21] and entomopathogens [22], involves carrying out tests in laboratories and/or in semi-natural conditions with larvae which need to be kept alive during identification [20].…”