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.
Highlights
Insecticides, including high-impact ones, such as neonicotinoids[1], are used prophylactically worldwide in maize and other annual crops[2]
A longer period of study using more consistent methods might have revealed significant associations between click beetles trapped in previous years and wireworm population levels at Year 0 (Y0), information that may have provided a useful estimate of the actual damage risk for crops, especially by species such as A. obscurus and A. sputator, which move much less than A. lineatus[17]
The received operating characteristic (ROC) analysis detected a threshold of 458 for the number of A. brevis adults captured in the same year (Y0) plant damage was recorded, with method accuracy being 55% (P = n.s., Table 1)
Summary
Insecticides, including high-impact ones, such as neonicotinoids[1], are used prophylactically worldwide in maize and other annual crops[2]. 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]. The materials and methods described in the aforementioned study[16] had major constraints, as fields were observed for one year only, methods for assessing wireworm density were not standardized, and key details, such as descriptions of trap management and methods for extracting larvae from soil cores, were missing All of these points are essential if results are to be compared effectively with other papers on the same issue. We believed that it would enable us to identify fields with a higher probability of hosting wireworm populations that could cause yield reduction and economic damage, with the aim of applying treatments only where necessary
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