**5. Conclusions**

Although many key aspects are still to be made available—the number of missing damage thresholds is astonishing—the bulk of available information allows us to immedi-

\* ately implement effective IPM strategies against wireworms. A practical IPM procedure for efficient wireworm managemen<sup>t</sup> (including damage thresholds) has been described for maize in Europe [57,58]. This IPM procedure is currently implemented on thousands of hectares of cultivated land [7]. In Table 3, the IPM tactics and tools currently available for reducing the risk of wireworm crop damage to susceptible crops are classified according to their damage reduction potential and their current implementation status. "Already applied" practices with proven efficiency and practicability can be immediately implemented, while "under development" strategies are promising ones that still need large-scale evaluation and adaptations to variable practical conditions. "Under study" strategies comprise promising ongoing research, with no or negligible practical implementation, but they are being considered for possible future uses.

**Table 3.** Alternative strategies that can be applied to maintain wireworm density below damage thresholds according to results of continuous monitoring. One or more practices can progressively be applied to push back wireworm population levels. Under study: promising ongoing research but no or negligible practical implementation. Under development: limited practical applications; ongoing evaluations to adapt solution to variable practical conditions. Already applied: significant widespread implementation.


Continuous population level assessment according to IPM principles and selection of fields with low wireworm density. \*\* From [15].

> The IPM strategy level needed to continuously keep wireworm populations below damage thresholds, and the lowest possible cost can be pursued by implementing "flexible IPM packages". These should be made up of two or more practices applied at the same time, provided that the different practices are compatible and that they have additional effects on wireworm population and crop-damage reduction. No incompatibilities between the strategies listed in Table 3 have been reported. The first fixed IPM practice, common to any flexible package, should be continuous pest population monitoring with low-cost tools,

such as pheromone traps (see Section 2.2.1), with complementary local bait trap wireworm monitoring before a susceptible crop seeding when needed (see Section 2.2.2).

IPM flexible packages may vary according to population levels assessed with continuous monitoring. Low-risk rotation should be implemented (see Section 3.1), in accordance with the prevalent wireworm species, including non-favoring crops and tillage when susceptible pest instars (eggs and young larvae) occur in the soil. If monitoring still assesses risky population levels and/or significant wireworm crop damage has been observed, other strategies should be added. These include the incorporation of biofumigant defatted seed meals (pellets) or biocidal plants. Farmers should find the package most suitable to their specific conditions and modulate package strategies as per wireworm population dynamics monitored by YATLORf traps (Table 3). Therefore, a general flexible IPM of wireworms should comprise two main phases: (1) a risk assessment that considers all the relevant agronomic and climatic characteristics that can be typically achieved by continuous monitoring of click-beetle populations with pheromone traps. Complementary wireworm field monitoring is advisable when risk assessment has identified the presence of risk factors and/or high beetle populations and/or previous wireworm crop damage; (2) the implementation of one or more of the practices listed in Table 3 in order to maintain or to restore wireworm populations below levels that cause significant damage to the susceptible crops in the planned rotation. Regardless of whether specific damage thresholds are available, farmers might find the IPM flexible package best suited to each homogeneous cultivated area on their farm by modulating preventative and rescue strategies (Table 3) so that susceptible crop damage is negligible. This should also require costs and the overall economic sustainability of alternative strategy implementation to be considered.

In order to make farmers comfortable with IPM implementation risks, insurance tools covering these risks may be particularly useful and supported by legislation (mutual funds). Mutual fund compensation is commensurate with the financial resources of the fund. The fund stock is increased by savings in forecast costs and covers risks that private insurance companies currently do not, e.g., climatic adversities such as flooding and damage by wild animals and pests, just before and after the emergence of arable crops. The first implementations are underway in Italy and the results are promising [220].

While important advances have been recently made, many gaps remain in the setting up of a complete and efficient IPM framework to deal with wireworm issue in crops. Indeed, significant progress is still needed on many aspects of our knowledge. The association between wireworm density and harmfulness to various crops in different conditions is still missing for several species. This impedes the establishment of precise, verifiable thresholds for each crop × wireworm species in the various cultivated contexts and areas. Knowledge on behavioral ecology of adults remains highly fragmentary, notably concerning their dispersal (distance, orientation) or their choice of egg-laying site. Progress would be useful if we are to better understand colonization processes and to address wireworm risk at landscape scale. Abiotic and biotic soil parameters (e.g., organic matter content) that favor the survival and development of larvae should be specified in order to identify suppressive soils (i.e., soils that maintain wireworm populations at low levels naturally). This would mainly require assessing the main natural causes of larval mortality, including parasitism and predation, and a better understanding of larval trophic ecology and life-cycle. In terms of agricultural sciences, studies on various promising practices, including tilling, use of biofumigants, or setting up companion plants, should be fostered. In addition, despite some promising preliminary results, varietal tolerance/resistance has, to date, received little attention. Finally, holistic decision-support tools for the implementation of IPM should be rendered available to farmers. Eventually, precise and verifiable targets for IPM implementation for each crop × wireworm species in the various cultivated areas [7] should be identified, with any relevant socio-economic aspects also being considered.

**Author Contributions:** Conceptualization, S.P., R.L.C., J.L., M.P. and L.F.; writing—original draft preparation, S.P., R.L.C., J.L., M.P. and L.F.; writing—review and editing, S.P., R.L.C., J.L., M.P. and L.F.; project administration, S.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the French Office for Biodiversity (STARTAUP project); the "Groupement National Interprofessionnel des Semences et plants" (TAUPIN LAND project); and the French Ministry for Agriculture and Food for funding the TAUPIC project (CASDAR n◦20ART1568739). The APC was funded by the Institute for Genetics, Environment and Plant Protection (IGEPP).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** S.P., R.L.C. and M.P. acknowledge the French Office for Biodiversity for funding the STARTAUP project ("Design of alternative strategies for controlling wireworm damage in maize crops"); the "Groupement National Interprofessionnel des Semences et plants" (GNIS) for funding the TAUPIN LAND project; and the French Ministry for Agriculture and Food for funding the TAUPIC project (CASDAR n◦20ART1568739). S.P. thanks Julien Saguez (CEROM, Quebec, Canada) for providing useful information about the web application VFF-QC and Leyli Borner (INRAE) for her assistance in producing Figure 1. R.L.C. and S.P. are grateful to Philippe Larroudé (Arvalis) and Jean-Claude Ogier (INRAE) for providing photographs.

**Conflicts of Interest:** The authors declare no conflict of interest.
