Conservation agriculture affects multitrophic interactions driving the efficacy of weed biological control

International audience1. Biological control is a key ecosystem service in arable lands, but its effectiveness varies according to environmental and biotic contexts. Cascading interactions between several trophic levels can affect natural enemies and their efficacy.2. Here, we analysed how multitrophic interactions drive weed seed control under contrasting farming systems and landscapes. In particular, we analyse how the presence of higher-order predators and alternative prey affects the weed seed consumption by seed predators. We monitored 30 cereal fields organised into 15 pairs, each comprising one conventional and one conservation agriculture field, sampled along a gradient of proportion of conservation agriculture in the landscape.3. We found that local and landscape management under conservation agriculture favours the presence of seed predators like carabids and rodents, higher-order predators like shrews and alternative animal prey. Weed seed predation is promoted by conservation agriculture through an increase in the number of seed predators. However, alternative animal prey reduces the efficacy of carabids to consume seeds, probably due to a prey-switching behaviour. Similarly, shrews negatively affect the activity-density of carabids, resulting in an indirect negative effect on seed predation.4. Synthesis and applications: Our study highlights that the implementation of conservation agriculture can improve the provision of biological control but the resulting effect may be partially limited by the increased complexity of trophic interactions. The different trophic levels respond to local management and/or the surrounding landscape with cascading effects on the delivery of weed control. Our study highlights the importance of considering not only the direct effects of seed predators, but also the indirect effects of higher-order predators and alternative prey when predicting the level of weed biological control

Biological protection against grape berry moths. A review

Grape is a major crop, covering 7.5 M ha worldwide, that is currently being confronted with three main challenges: intensive pesticide use that must be reduced, invasion by new pests/diseases, and climate change. The biological control of pests and vectors would help address these challenges. Here, we review the scientific literature on the biological control of grape moths by macroorganisms (excluding nematodes). Two components, biological control with an active human role, mainly using biocontrol agents through inundation or inoculation, and conservation biological control, are considered. The major points are the following. (1) Tortricid grape moths seriously damage grapes worldwide, causing yield losses and quality reduction. The more geographically widespread species, Lobesia botrana, continues to extend its range, invading South American and, more recently, North American vineyards. (2) Parasitoids and predators (including arthropods, birds, and bats) that can control grape pests are very diverse. (3) Different methods exist to assess pest control efficiency in the field but some of them remain to be developed. (4) Environmental factors, including host plants, landscape, grass or floral covers, and organic practices, affect the natural control of grape moths. (5) Pest resistance to parasitoids strongly depends on their immune system, which is controlled by the host plant. Future climate changes may modify this tritrophic interaction and thus affect biological control strategies. We conclude that biological control has a great deal of potential in viticulture and that addressing these key factors would improve the efficiency levels of biological control strategies. This would help growers and stakeholders to significantly reduce insecticide use in vineyards