Wireworms, the larvae of click beetles (Coleoptera: Elateridae), are abundant soil-dwelling insects which attack the below-ground parts of a wide range of crops. To date, wireworms are considered to be one of the most difficult pests to control. This is mainly due to their extensive vertical movements in the soil column, going deeper when conditions are adverse and moving to the upper soil layers for feeding. These vertical migrations make it particularly hard to estimate potential yield loss, define damage thresholds and implement effective control measures. There are at least nine pestiferous species of elaterid larvae occurring in European agriculture. Most of these species are indistinguishable for the naked eye and cause similar damage symptoms, but their biology and ecology varies considerably which calls for speciesspecific control tactics. The main objective of the ElatPro project is to develop and implement a forecasting model to predict wireworm activity in the topsoil. Due to technical problems with data loggers at most trial sites weather data had to be subsequently obtained from weather stations and laboriously transferred into the correct format. Furthermore, difficulties occurred with molecular identification method (PCR) and time-consuming morphological wireworm identification was required for most individuals. Due to the later delivery of the necessary data the development and parametrization of the model functions will be finished by the end of 2019 by ZEPP. This model can then be used by farmers and consultants as a decision-making tool in order to determine the optimal time to deploy pest control measures to combat wireworms. To achieve these objectives an open land monitoring was conducted to detect wireworm activity in the uppermost soil layers at testing areas in Germany, Austria, Italy, Belgium, France and Switzerland. Monitoring guidelines were issued at the start of the project in order to ensure uniform monitoring processes across all testing areas. The survey of wireworm activity in the uppermost soil layers are conducted using bait traps and soil samples. At some sites the adult beetles’ flight periods were documented at selected locations with the help of pheromone traps. Records were taken over the entire vegetation period with regards to the soil climate, vegetation development and all soil cultivation measures implemented, as well as crop rotation.
In addition to open land monitoring, semi-field and laboratory testing were carried out. Semifield cages allowed the composition of the wireworm population to be varied as desired in terms of the species composition and larval stages present, thereby making it possible to investigate various population scenarios at the same location. The laboratory testing investigated the individual factors that influence wireworms’ migratory behaviour. Furthermore, a new method to determine wireworms on a species level through amplification of DNS (LAMP method) was developed.
Laboratory experiments
- The results of the laboratory tests have shown that the influence of soil moisture on the location of wireworms within the soil column mainly depends on the soil type. A. ustulatus had slightly lower soil moisture requirements than A. obscurus and was found in both, very dry and very humid areas. While A. lineatus was mainly found in warmer areas at temperatures of 13°C to 25°C, A. ustulatus and A. obscurus were found in a range of 6°C - 25°C, whereby the optimum temperature of both species was about 13°C (AGES).
- The food choice indicated that Brassicaceae are not preferred food plants, while the no-choice trials indicated that the wireworm growth is at least in tendency reduced (JKI).
- Volatile substances (VOCs) were identified from the roots of two maize varieties having experienced contrasted levels of wireworm infestation in the field. The results showed that the less susceptible variety released a more diverse blend of VOCs, including large amounts of hexanal, heptanal and 2,3-octenanedione. Dual-choice laboratory bioassays showed that wireworms were strongly attracted to VOCs released by maize roots. However, when wireworms were offered both maize varieties, no preference was detected, contrasting with the field results. Therefore, VOCs may not be the only cues influencing the host selection of wireworms (University of Liege).
- Currently, we are testing an attract-and-kill system using as biocontrol agent the entomopathogenic nematodes (EPNs) and natural plant extract (maize and potatoes) incapsulated in alginate beads, as attractants. The system is killing faster respect to a classical EPNs screening but it still needs further studies and a better EPNs candidate (University of Liege). Carbon dioxide might pay a key role in this.
- By using LAMP technology, a new and fast molecular identification technique, the presence of crop-damaging wireworm species of the genus Agriotes can be determined quickly and in the field.
Specific primers have been developed for A. sputator on the one hand and A. lineatus/obscurus on the other hand. The latter two species cannot be distinguished with certainty by the LAMP method.
This is not a problem in terms of damage prediction and advising the growers. Currently, the LAMP primers are validated on the basis of foreign Agriotes populations (ILVO).
New model approaches and use of ElatPro project results
- Based on the monitoring data from Eastern Austria, a new model approach for the simulation of A. ustulatus activity in the topsoil was developed to supplement the existing models. This first model version shows promising hit rates, but activity rate data of several years and sites are necessary for further development (MELES).
- A spatially explicit mechanistic model describing the pest population dynamics in both aerial and soil compartments along the entire click beetle life cycle was developed. IGEPP currently use it to study in silico the role of grasslands in soil-dwelling pest infestation within a dynamic agricultural mosaic with the aim of bringing an original contribution to the prospect of innovative landscapescale management strategies. (IGEPP).
- Since the SIMAGRIO-W model algorithm is implemented in the system, ISIP serves as a hub for field and weather data. Field data collection is supported by a multi-language mobile app (Collector for ArcGIS) adapted to the project’s needs whereas the model development is assisted by importing the soil temperature and moisture data sampled at the trial sites. The final result – a regionally adapted version of the model – is disseminated in an intuitive user interface to practitioners and advisors.
- The further development of SIMAGRIO-W on the basis of the knowledge gained in the project has so far proved to be insufficient in practice. Subsequently, information on the biology of the pest (e.g. temperature sums required for larval development) will be integrated into the model (ZEPP).
