Adrien Rusch

Flow and stability of natural pest control services depend on complexity and crop rotation at the landscape scale

Increasing landscape complexity can enhance biodiversity and ecosystem services in agroecosystems. However, policies based on conversion of arable land into semi-natural habitats to increase landscape complexity and ecosystem services can be difficult to implement. Although it appears to be a promising management option, nothing is known about the effect of increasing landscape diversity through crop rotations on the delivery of ecosystem services. In this study, we examined how landscape complexity and crop rotation intensity in the landscape at different spatial scales affect the flow and the stability of natural pest control services in barley fields using manipulative cage experiments. Exclusion experiments revealed that natural enemies can have a strong impact on aphid population growth and that the delivery of pest control services is strongly dependent on the landscape context. We found that the overall level of pest control increased with landscape complexity and that this effect was independent of crop rotation intensity. In addition, the within-field stability in pest control services increased with crop rotation intensity in the landscape, although stability in parasitism rates decreased. Multiple spatial scales analyses showed that the mean level of natural pest control was best predicted by landscape complexity at the 0 center dot 5-km and the 1-km spatial scales. The stability in overall pest control decreased with proportion of ley at the 2 center dot 5-km and the 3-km spatial scales. Synthesis and applications. Our study disentangled, for the first time, the relative effects of landscape complexity and crop rotation intensity on the delivery of an ecosystem service. We show that combined management of semi-natural habitat and crop rotation can stabilize and enhance natural pest control in agricultural landscapes. Our findings have important implications in terms of management options to maintain and enhance ecosystem services in agroecosystems. They suggest that conservation of heterogeneous landscapes, characterized by a higher proportion of semi-natural habitats such as pastures and relatively small fields, is essential for maintaining and enhancing effective biological control in agroecosystems.

Management intensity at field and landscape levels affects the structure of generalist predator communities.

Agricultural intensification is recognised as a major driver of biodiversity loss in human-modified landscapes. Several agro-environmental measures at different spatial scales have been suggested to mitigate the negative impact of intensification on biodiversity and ecosystem services. The effect of these measures on the functional structure of service-providing communities remains, however, largely unexplored. Using two distinct landscape designs, we examined how the management options of organic farming at the field scale and crop diversification at the landscape level affect the taxonomic and functional structure of generalist predator communities and how these effects vary along a landscape complexity gradient. Organic farming as well as landscapes with longer and more diversified crop rotations enhanced the activity-density of spiders and rove beetles, but not the species richness or evenness. Our results indicate that the two management options affected the functional composition of communities, as they primarily enhanced the activity-density of functionally similar species. The two management options increased the functional similarity between spider species in regards to hunting mode and habitat preference. Organic farming enhanced the functional similarity of rove beetles. Management options at field and landscape levels were generally more important predictors of community structure when compared to landscape complexity. Our study highlights the importance of considering the functional composition of generalist predators in order to understand how agro-environmental measures at various scales shape community assemblages and ecosystem functioning in agricultural landscapes.

Avian pest control in vineyards is driven by interactions between bird functional diversity and landscape heterogeneity

Insectivorous birds are increasingly recognized for the crucial pest control services they provide to agroecosystems. While both the foraging activity and functional diversity of birds are enhanced by multiscale habitat heterogeneity, little is known about how these relationships may influence avian top‐down control of insects. Specifically, interactive effects of bird community structure and habitat heterogeneity on pest control across spatial scales have rarely been explored. We sampled bird communities and measured avian predation on plasticine model prey, as a proxy for lepidopteran pest control, in 20 vineyards of south‐western France. Vineyards differed both in sward heterogeneity at the local scale and amount of surrounding semi‐natural habitats at the landscape scale. Functional diversity metrics and community‐weighted mean traits were computed for bird communities based on a species–trait table including diet, foraging method, nesting site, migration strategy, laying date, home range size, clutch size and body mass. We used mixed models to test for the interacting effects of habitat heterogeneity and bird functional diversity on avian predation rates of plasticine prey. Contrary to expectations, bird functional diversity decreased with landscape‐scale heterogeneity, but was higher in vineyards managed with heterogeneous sward structures. In contrast, foliage‐gleaning insectivores were more abundant in landscapes supporting more semi‐natural habitats, suggesting an increase in their contribution to pest control along the landscape heterogeneity gradient. Accordingly, we found that avian predation on plasticine prey increased with bird functional evenness both in more heterogeneous vineyards at the local scale and in landscape mosaics supporting more semi‐natural habitats. Synthesis and applications. Our study demonstrates that habitat heterogeneity at both local and landscape scales influenced avian insectivory in vineyard agroecosystems by interacting with bird community structure. It provides important insights for ecological intensification in vineyards, pointing out that management options need to be adapted to both the functional composition of local bird communities and landscape context. We suggest that both on‐field and off‐field management can be used to enhance natural pest control services provided by birds in vineyards, especially by favouring sward heterogeneity and patches of semi‐natural habitats within large vineyard stands at the landscape scale.

Nutritional state of the pollen beetle parasitoid Tersilochus heterocerus foraging in the field

Many laboratory studies have demonstrated that parasitoids of various species depend on sugar sources such as nectar or honeydew. However, studies about nectar acquisition by parasitoids foraging in the field are scarce. Tersilochus heterocerus Thomson is one of the more abundant and widespread parasitoids of the pollen beetle (Meligethes aeneus F.) but nothing is known about the nutritional ecology of this species. In this study we examined the nutritional state of T. heterocerus at the time of emergence and at various time periods throughout the season while foraging in the field using high-performance anion-exchange chromatography. We found that: (i) T. heterocerus emerge with relatively small amounts of sugar, composed mainly of trehalose, glucose and fructose; (ii) the first parasitoids caught just after they appeared in the field at the beginning of oilseed rape flowering had already consumed significant amounts of sugar reserves; and (iii) the total amount of sugar at the end of flowering was always significantly higher than the total amount of sugar at the beginning of flowering. This study provides valuable insights into the acquisition of sugar in the field by the parasitoid T. heterocerus and suggests that nectar acquisition takes place in the oilseed rape field or in the surrounding landscape.

Local and landscape effects of agricultural intensification on Carabid community structure and weed seed predation in a perennial cropping system

ContextThe effects of agricultural intensification on service-providing communities remain poorly studied in perennial cropping systems. However, such systems differ greatly from annual cropping systems in terms of spatio-temporal dynamics and levels of disturbance. Identifying how land use changes at different scales affect communities and ecosystem services in those habitats is of major importance.ObjectivesOur objectives were to examine the effects of local and landscape agricultural intensification on ground beetle community structure and weed seed predation services.MethodsWe examined the effects of local vegetation management and landscape context on ground beetle community structure and weed seed predation in 20 vineyards of southwestern France in 2013 and 2014. Vineyards were selected along a landscape complexity gradient and experienced different management of local vegetation.ResultsThe activity-density of ground beetles decreased with increasing landscape complexity while species richness and evenness remained unchanged. Phytophagous and macropterous species dominated ground beetle communities. Seed predation was positively related to the activity-density of one species, Harpalus dimidiatus, and was not affected by local management or landscape context. We found that within-year temporal diversity in ground beetle assemblages increased with landscape complexity.ConclusionsOur study shows that increasing the proportion of semi-natural habitats in vineyard landscapes enhances the temporal diversity of ground beetles. However, we also found that measures targeting specific species delivering biological control services are a reasonable strategy if we are to maximize natural pest control services such as weed seed regulation to support crop production and reduce agrochemical use.

Conserving species‐rich predator assemblages strengthens natural pest control in a climate warming context

Recent evidence has shown that a consideration of multiple drivers is important if we want to understand how ecosystem functioning will respond to global change. In the present study, we used a substitutive approach to examine how two major components of global change, warming and predator diversity, affect the top‐down control of two phytophagous insect pests. Predator assemblages were created using a substitutive design to give three single‐species treatments (low diversity) and one three‐species treatment (high diversity) under two temperature treatments (current seasonal temperature and an increase of +3°C over current temperatures). The results obtained indicate a shift from substitutive to complementarity effects among predatory species with experimental warming. Experimental warming revealed complementarity between the predatory species in diverse assemblages because higher predation rates on both prey species were found in the high diversity treatment compared with what was expected based on low diversity treatments at the same temperature. Our analyses of prey selectivity provided evidence that resource‐niche partitioning is involved in the emergence of functional complementarity under warming. The present study highlights the importance of maintaining diverse predator assemblages if we want to increase natural pest control services in agroecosystems and reduce dependence on agrochemicals in a climate change context.

Interactive effects of pests increase seed yield.

Abstract Loss in seed yield and therefore decrease in plant fitness due to simultaneous attacks by multiple herbivores is not necessarily additive, as demonstrated in evolutionary studies on wild plants. However, it is not clear how this transfers to crop plants that grow in very different conditions compared to wild plants. Nevertheless, loss in crop seed yield caused by any single pest is most often studied in isolation although crop plants are attacked by many pests that can cause substantial yield losses. This is especially important for crops able to compensate and even overcompensate for the damage. We investigated the interactive impacts on crop yield of four insect pests attacking different plant parts at different times during the cropping season. In 15 oilseed rape fields in Sweden, we estimated the damage caused by seed and stem weevils, pollen beetles, and pod midges. Pest pressure varied drastically among fields with very low correlation among pests, allowing us to explore interactive impacts on yield from attacks by multiple species. The plant damage caused by each pest species individually had, as expected, either no, or a negative impact on seed yield and the strongest negative effect was caused by pollen beetles. However, seed yield increased when plant damage caused by both seed and stem weevils was high, presumably due to the joint plant compensatory reaction to insect attack leading to overcompensation. Hence, attacks by several pests can change the impact on yield of individual pest species. Economic thresholds based on single species, on which pest management decisions currently rely, may therefore result in economically suboptimal choices being made and unnecessary excessive use of insecticides.

Deployment of organic farming at a landscape scale maintains low pest infestation and high crop productivity levels in vineyards

1.Organic farming is a promising way to reduce pesticide use but increasing the area under organic farming at the landscape scale could increase pest infestations and reduce crop productivity. Examining the effects of organic farming at multiple spatial scales and in different landscape contexts on pest communities and crop productivity is a major step in the ecological intensification of agricultural systems. 2.We quantified the infestation levels of two pathogens and five arthropod pests, the intensity of pesticide use and crop productivity in 42 vineyards. Using a multiscale hierarchical design, we unraveled the relative effects of organic farming at both field and landscape scales from the effects of semi-natural habitats in the landscape. 3.At the field scale, pest communities did not differ between organic and conventional farming systems. At the landscape scale, increasing the area under organic farming did not increase pest infestation levels. 4.Three out of seven pest taxa were affected both by local farming systems and the proportion of semi-natural habitats in the landscape. Our findings revealed that the proportion of semi-natural habitats reduced pest infestation for two out of seven pest taxa, while the others were unaffected. 5.Organic vineyards had much lower treatment intensities, very similar levels of pest control and equal crop productivity levels. 6.Synthesis and Applications. Our results clearly indicate that policies promoting the development of organic farming in conventional vineyard landscapes will not lead to greater pest and disease infestations but will reduce the pesticide treatment intensity and maintain crop productivity. Moreover, the interactions between semi-natural habitats in landscape and local farming practices suggest that the deployment of organic farming should be adapted to landscape contexts. This article is protected by copyright. All rights reserved.

Conservation Biocontrol: Principles and Implementation in Organic Farming

Conventional agricultural systems have become more intensive and pesticide-dependent over the last few decades. The contamination of the environment by pesticides, the use of mineral fertilisers, and habitat loss in many agroecosystems have led to a drastic decrease in plant and animal biodiversity. Ecosystem services provided by functional biodiversity (e.g., pollination, biological pest control) have also been negatively impacted. Conservation biocontrol aims to preserve and promote natural enemies to enhance pest control, avoid pest outbreaks and reduce pesticide reliance. However, despite a consensus on the main underlying principles, intentional practical applications are still rare. It is assumed that the diversity of habitats and resources in agroecosystems enhances the diversity and/or effectiveness of the natural enemies of pests. In this article, we argue that organic farming (OF) provides a promising framework for increasing conservation biocontrol at field and farm scales in agricultural landscapes. We looked at most of the commonly used OF practices at different spatio-temporal scales and discussed their effects on pest populations, natural enemy communities and biocontrol in agroecosystems. Several OF management practices such as crop diversification, use of organic fertilisers, diversification of resource plants at the field or landscape scales and land-use management are examined in our review. We particularly focused on possible strategies to enhance pest control measures in two case studies (i.e., orchard and annual crops) and discussed how and at which scales such strategies should be implemented. In the end, we identified knowledge gaps and bottlenecks that, if resolved, would help to enhance conservation biocontrol and applications in OF systems that aim to maximise both bottom-up (through plants) and top-down (through natural enemies) processes.

Ecology for Sustainable and Multifunctional Agriculture

The Green Revolution and the introduction of chemical fertilizers, synthetic pesticides and high yield crops had enabled to increase food production in the mid and late 20th. The benefits of this agricultural intensification have however reached their limits since yields are no longer increasing for many crops, negative externalities on the environment and human health are now recognized and economic inequality between farmers have increased. Agroecology has been proposed to secure food supply with fewer or lower negative environmental and social impacts than intensive agriculture. Agroecology principles are based on the recognition that biodiversity in agroecosystems can provide more than only food, fibre and timber. Hence, biodiversity and its associated functions, such as pollination, pest control, and mechanisms that maintain or improve soil fertility, may improve production efficiency and sustainability of agroecosystems. Although appealing, promoting ecological-based agricultural production is not straightforward since agroecosystems are socio-ecosystems with complex interactions between the ecological and social systems that act at different spatial and temporal scales. To be operational, agroecology thus requires understanding the relationships between biodiversity, functions and management, as well as to take into account the links between agriculture, ecology and the society. Here we review current knowledge on (i) the effect of landscape context on biodiversity and ecosystem functions and (ii) trophic and non-trophic interactions in ecological networks in agroecosystems. In particular, many insights have been made these two previous decades on (i) the interacting effects of management and landscape characteristics on biodiversity, (ii) the crucial role of plant diversity in delivering multiple services and (iii) the variety of ecological belowground mechanisms determining soil fertility in interaction with aboveground processes. However, we also pinpointed the absence of consensus on the effects of landscape heterogeneity on biodiversity and the need for a better mechanistic understanding of the effects of landscape and agricultural variables on farmland food webs and related services. We end by proposing new research avenues to fill knowledge gaps and implement agroecological principles within operational management strategies.