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Highlights: [•] Aquatic–terrestrial and crop–noncrop linkages are conceptually similar. [•] Exchanges in agroecosystems are governed by natural enemy production and dispersal. [•] Donor habitats on the landscape determine the coverage of dispersal. [•] Land-cover/use and climate change will impact habitats, natural enemy exchange. [Copyright &y& Elsevier]

Agricultural landscapes in North America have developed through complex interactions of biophysical, socioeconomic and technological forces. While they can be highly productive, these landscapes are increasingly simplified, causing biodiversity loss. As a result, ecosystem services associated with biodiversity are being dismantled. Agricultural landscape structure arises from collective decisions of farmers over long time periods, which are usually not intentionally coordinated beyond the farm scale. Regaining ecosystem services will require active efforts to intentionally redesign landscapes, in part based on ecological evidence about relationships between landscape structure and ecosystem services. Here we focus on services provided by arthropods and how to foster them at landscape scales. We first provide a brief history of how agricultural landscape structure in temperate North America developed and review the landscape-scale ecological drivers underpinning arthropod-based ecosystem services. We then propose ecological and social principles for designing agricultural landscapes, based on the ecological evidence we reviewed and on previous efforts in agricultural landscape design. Finally, we look ahead to discern prospects for putting agricultural landscape design into practice, including ecological, technological and policy opportunities. To reap benefits from arthropod-based services, future agricultural landscapes will need to increase in structural heterogeneity and diversity across multiple dimensions including crop, farmer and consumer diversity. A number of knowledge gaps persist, including how to design landscapes at spatial scales that are relevant to service providers, identifying areas of overlap or conflict between design for ecosystem services and for biodiversity conservation more broadly and navigating the social and political processes needed to implement landscape design. [ABSTRACT FROM AUTHOR]

Abstract: Cultivation of biofuel crops could change agricultural landscapes, affecting natural enemies at multiple scales. We sampled five natural enemy families with sticky cards in three model biofuel habitats (corn, switchgrass and prairie; n =60) across southern Michigan and Wisconsin, comparing captures between habitats and relating them to the area of forest, annual crop and herbaceous perennial habitat in the landscape within 2km of sites. In a first analysis, we compared Coccinellidae assemblages between habitats and examined the impact of habitat type and landscape composition on species richness and abundance. Results showed that, at the habitat scale, perennial grasslands supported a greater abundance of uncommon, native coccinellids and hosted distinct species assemblages compared to corn. At a broader scale, abundances of exotic and uncommon native ladybeetles responded differently to landscape composition, decreasing with the area of herbaceous perennials and annual crops, respectively. In a second analysis, we related family-level abundances of Anthocoridae, Syrphidae, Dolichopodidae and Chrysopidae to habitat type and landscape composition. Dolichopodids were more abundant in grasslands, while anthocorid and syrphid abundance increased over fivefold with the area of herbaceous, perennial habitat in the landscape surrounding corn, but not grassland, sites. These findings suggest that perennial grasslands used for bioenergy production could conserve natural enemies which are less abundant in corn, the dominant biofuel in existing landscapes. Moreover, cultivating annual cropland with herbaceous, perennial habitats could affect the abundance of natural enemies in existing crops and alter the suitability of entire landscapes for these beneficial taxa. [Copyright &y& Elsevier]

Abstract: Since the arrival of the soybean aphid, Aphis glycines, to the U.S. in 2000, year to year abundances have varied substantially. Although, field studies have suggested that several resident generalist predators have the ability to suppress A. glycines populations, factors responsible for its population dynamics remain unclear. For natural enemies to regulate herbivore populations, predation rates must increase as prey population densities increase (i.e., density dependence). Experiments were conducted in 2004–2006 to assess the ability of the existing natural enemy community to exert density-dependent effects on A. glycines populations. Aphid densities were manipulated on individual plants (transplanted to the field) or in small plots to contain a range of aphid densities from low (10 per plant) to high (>1000 per plant). Populations were then monitored weekly. Caged controls were included to measure population growth in the absence of predators. In 2006, an additional treatment was included to quantify the proportion of aphids emigrating from plants. In all experiments, a strong density-dependent decline in population abundance was observed as aphid populations on plants with low initial densities (<50 aphids per plant) tended to increase while plants with high initial densities (>100 aphids per plant) decreased by as much as two orders of magnitude over a 1–2 week period. We estimate that fewer than 5% of aphids emigrated from plants when aphid densities were below 4000 per plant. This suggests that the extreme declines in aphid populations over these brief experiments were not due to aphids leaving plants, but rather, due to an aggregative response of predators to high density prey populations. Given the rapidity and degree of density-dependent population decline in three consecutive years of study, we suggest the resident community of natural enemies in Midwestern soybean may have great potential to regulate soybean aphid populations. [Copyright &y& Elsevier]

• High-throughput amplicon sequencing (HTS) was used to characterize lady beetle diets. • Prey detection was observed in 33–55% of field and lab specimens, respectively. • Omnivory was prevalent in corn where prey richness and breadth were low. • Omnivory was lower in prairie where prey richness and breadth were high. • HTS is a useful tool for assessing biocontrol potential of predators in the field. Determining feeding relationships is central to understanding biological control potential in the field. However, methods to differentiate actual (or realized) feeding relationships from potential feeding relationships is lacking especially for small, generalist predators such as lady beetles. In this study, we used DNA metabarcoding approaches to characterize actual feeding relationships of lady beetles (Coccinellidae) in the field and validated our methods with a lab study. We first asked whether high-throughput amplicon sequencing (HTS) can characterize diets of lady beetles ranging from monotypic diets to diverse diet mixtures in the lab. We then examined whether diet composition and breadth of lady beetles collected from different habitat types in southern WI varied between monocultures of soybean and corn, diverse tallgrass prairie, and urban habitats. Lastly, we asked whether different body or tissue types (partial-body versus whole-body specimens) would change the likelihood of prey detection for both studies. In our controlled lab study, we found that HTS can accurately assess diet composition and diet breadth for lady beetle populations, but at the individual level, HTS has limitation for individuals feeding on more than three species of prey at any given time. In our field study, we documented lower prey richness and diet breadth in corn compared to soybean and grassland, and greater prey DNA in regurgitants than in whole-body specimens. Finally, we found that reduced diet diversity was associated with an increased prevalence of intraguild predation, but that habitat and prey diversity are not necessarily correlated. The prey detection rates (proportion of specimens with prey DNA) in our study were comparable to other studies (55% in the lab study, 33% in field study) and varied with diet composition and habitat type. The relatively low detection rates suggest that many consumer individuals would need to be assayed to fully assess diet diversity, especially in diverse systems. [ABSTRACT FROM AUTHOR]

Abstract: Replacing cropland with non-crop vegetation can affect predation of crop pests through multiple mechanisms, with varying implications for management. Prairie grasses have been planted for on-farm conservation across the United States. We examined the potential impacts of replacing cropland with prairie grasses on predation of Leptinotarsa decemlineata (Say), examining underlying mechanisms. Experiments disentangled changes in the area and edge-to-area ratio of potato patches from the addition of prairie grasses and determined if effects were mediated through herbivore or predator trophic levels. In 2007 and 2008, we compared predation of L. decemlineata eggs, egg and adult densities, and densities of natural enemies between (1) 15×20m monocultures of potatoes, (2) smaller patches (2×20m) surrounded by 15×20m of bare ground and (3) small patches in a 15×20m background of prairie grass. Predation increased fourfold in potatoes surrounded by native grasses compared to potato monocultures, an effect not explained by changes in potato area. Moreover, predation was elevated along edges of monoculture plots within 5m of adjacent grasses but was consistently lower in their center and opposing edge, suggesting that proximity to grasses, and not edges in general, affected predation. Increases in predation were correlated with increased harvestmen (Opiliones) and spider (Araneae) abundance in native grasses. An experiment suggested the numerical response of harvestmen was sufficient to explain the observed increase in predation. Reducing the distance between crop and non-crop vegetation could benefit generalist predators and increase their impact in crops. [Copyright &y& Elsevier]