Understanding the relationship between adult and larval Agriotes distributions: The effect of sampling method, species identification and abiotic variables

For successful management of invertebrate pest species it is important to understand the relationship between the distribution of above-belowground life stages, and the factors influencing them. Here we test the hypotheses that observed aboveground adult male click beetle (Coleoptera: Elateridae) and belowground larval (wireworm) distributions are related, species-specific, and influenced by sampling method and abiotic variables. Adult male and wireworm Agriotes species were sampled from grass/cropped fields in the South Hams, Devon, UK, using sex pheromone traps, soil cores and bait traps. A range of abiotic data was also collected. Redundancy Analysis (RDA) with forward selection was used to assess the influence of abiotic variables and the effect of sampling method on observed species distributions. Analyses were implemented with wireworm species grouped as a pest complex, and with wireworms identified genetically to species to determine the effect of grouping on the analysis outcome. There were no straightforward relationships between aboveground adult and belowground wireworm Agriotes species distributions, especially for A. lineatus, and these differed depending on the wireworm sampling method. Interspecific differences were observed between Agriotes and ‘non-Agriotes’ wireworm distribution, otherwise masked when wireworms were grouped together. Significant associations were found between adult and wireworm species’ distributions and specific abiotic variables. These results suggest that risk assessment of wireworm damage should be based on the collection of wireworm rather than adult samples, though there are still inconsistencies between wireworm sampling methods and knowledge gaps which need to be addressed to increase the reliability of these techniques.

► We studied factors affecting adult and larval click beetle species’ distribution.
► The relationship between adult and larval distribution changed with sampling method.
► Associations were found between species distributions and abiotic factors.
► Our results suggest it is important to identify both life stages to species.
► There are implications for the use of sex pheromone traps in risk assessment.