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The coexistence of closely related plant parasites is widespread. Yet, understanding the ecological determinants of evolutionary divergence in plant parasites remains an issue. Niche differentiation through resource specialization has been widely researched, but it hardly explains the coexistence of parasites exploiting the same host plant. Time-partitioning has so far received less attention, although in temperate climates, parasites may specialize on either the early or the late season. Accordingly, we investigated whether seasonality can also promote phenotypic divergence. For plant parasites, seasonality generally engenders periodic host absence. To account for abrupt seasonal events, we made use of an epidemic model that combines continuous and discrete dynamics. Based on the assumption of a trade-off between in-season transmission and inter-season survival, we found through an "evolutionary invasion analysis" that evolutionary divergence of the parasite phenotype can occur. Since such a trade-off has been reported, this study provides further ecological bases for the coexistence of closely related plant parasites. Moreover, this study provides original insights into the coexistence of sibling plant pathogens which perform either a single or several infection cycles within a season (mono- and polycyclic diseases, or uni- and multivoltine life cycles).

International audienceFarming practices are rarely considered in the description of agricultural landscapes. However, the variety of cropping systems creates a particular kind of heterogeneity which can strongly affect the diversity of species living in agro-ecosystems, and consequently the ecosystem services they provide. In this study, we investigate the effects of landscape composition and configuration of organic and conventional farming practices on three groups of aphids' natural enemies, compared to field habitat quality and land cover heterogeneity. A field survey was carried out in 2012 and 2013 in western France (Brittany). Ladybirds, carabid beetles and parasitoids were sampled in 40 pairs of organic and conventional winter wheat fields, distributed along a landscape gradient of organic farming areas. The relationships between farming practices and natural enemies were investigated with a PLS-path modeling approach, hardly ever used in ecology but presenting numerous advantages to analyze multivariate systems. Results showed that abundance and species richness of natural enemies were mainly affected by local farming practices, with a higher diversity in organic fields. To a lesser extent, landscapes also affected natural enemies, but only in relation to the length and configuration of hedgerows. Our results open up avenues for the design of agricultural landscapes since our results suggest that natural enemy diversity can be enhanced without a specific organization of organic fields. We discuss methodological issues regarding the description and the analysis of farming practices at the landscape scale. We argue that such investigations require high quality maps covering large spatial extents, and the use of statistical tools providing a good handling of complex relationships occurring in agro-ecosystems

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Crop-damaging wireworms-the soil-dwelling larvae of click beetles-have resurged in Europe over the past 15 years, particularly in French maize crops. There is currently no curative treatment available to control wireworms, and preventive treatments are mainly chemical. We therefore need to better understand factors that rule damage for developing agroecological control strategies. In this investigation, we tested the effect of agricultural practices and local landscape on wireworm damage in maize crops. We surveyed wireworm damage in 341 fields under various conditions in western France in 2011 and 2012. We used in particular a random forest algorithm to impute missing values and an automated model selection routine to select the best beta regression model. Our results show that the occurrence of grassland in the rotation increases wireworm damage. Tillage also shows a high influence, though varying with season and year. Wireworm damage is decreased by the presence of hedges or cultivated crops at the field border, whereas it is increased by the presence of grassland at the field border. Overall, our findings provide some insights to develop preventive solutions for the sustainable control of wireworms, as well as a framework for data processing to analyze a wide range of similar situations involving other crops and pests.

A large-scale survey was carried out in 336 French fields to investigate the influence of soil characteristics, climate conditions, the presence of wireworms and the identity of predominant species, agricultural practices, field history and local landscape features on the damage caused by wireworms in maize. Boosted regression trees, a statistical model originating from the field of machine learning, were fitted to survey data and then used to hierarchize and weigh the relative influence of a large set of variables on the observed damage. Our study confirmed the relevance of an early assessment of wireworm populations to forecast crop damage. Results have shown that climatic factors were also major determinants of wireworm damage, especially the soil temperature around the sowing date, with a strong decrease in damage when it exceeds 12°C. Soil characteristics were ranked third in importance with a primary influence of pH, but also of organic matter content, and to a lesser extent of soil texture.Field history ranked next, in particular our findings confirmed that a long lasting meadow appeared favourable to wireworm damage. Finally, agriculture practices and landscape context (especially the presence of a meadow in the field vicinity) were also shown to influence wireworm damage but more marginally. Overall, the predicted damage appeared highly correlated to the observed one allowing us to produce the framework of a decision-support system to forecast wireworm risk in maize crop.

Wireworms, the soil-dwelling larvae of click beetles (Coleoptera: Elateridae), comprise major pests of several crops worldwide, including maize and potatoes. The current trend towards the reduction in pesticides use has resulted in strong demand for alternative methods to control wireworm populations. This review provides a state-of-the-art of current theory and practice in order to develop new agroecological strategies. The first step should be to conduct a risk assessment based on the production context (e.g., crop, climate, soil characteristics, and landscape) and on adult and/or larval population monitoring. When damage risk appears significant, prophylactic practices can be applied to reduce wireworm abundance (e.g., low risk rotations, tilling, and irrigation). Additionally, curative methods based on natural enemies and on naturally derived insecticides are, respectively, under development or in practice in some countries. Alternatively, practices may target a reduction in crop damage instead of pest abundance through the adoption of selected cultural practices (e.g., resistant varieties, planting and harvesting time) or through the manipulation of wireworm behavior (e.g., companion plants). Practices can be combined in a global Integrated Pest Management (IPM) framework to provide the desired level of crop protection.