Douglas A. Landis

Landscape diversity enhances biological control of an introduced crop pest in the north-central USA

Arthropod predators and parasitoids provide valuable ecosystem services in agricultural crops by suppressing populations of insect herbivores. Many natural enemies are influenced by non-crop habitat surrounding agricultural fields, and understanding if, and at what scales, land use patterns influence natural enemies is essential to predicting how landscape alters biological control services. Here we focus on biological control of soybean aphid, Aphis glycines Matumura, a specialist crop pest recently introduced to the north-central United States. We measured the amount of biological control service supplied to soybean in 26 replicate fields across Michigan, Wisconsin, Iowa, and Minnesota across two years (2005-2006). We measured the impact of natural enemies by experimentally excluding or allowing access to soybean aphid infested plants and comparing aphid population growth over 14 days. We also monitored aphid and natural enemy populations at large in each field. Predators, principally coccinellid beetles, dominated the natural enemy community of soybean in both years. In the absence of aphid predators, A. glycines increased significantly, with 5.3-fold higher aphid populations on plants in exclusion cages vs. the open field after 14 days. We calculated a biological control services index (BSI) based on relative suppression of aphid populations and related it to landscape diversity and composition at multiple spatial scales surrounding each site. We found that BSI values increased with landscape diversity, measured as Simpsons D. Landscapes dominated by corn and soybean fields provided less biocontrol service to soybean compared with landscapes with an abundance of crop and non-crop habitats. The abundance of Coccinellidae was related to landscape composition, with beetles being more abundant in landscapes with an abundance of forest and grassland compared with landscapes dominated by agricultural crops. Landscape diversity and composition at a scale of 1.5 km surrounding the focal field explained the greatest proportion of the variation in BSI and Coccinellidae abundance. This study indicates that natural enemies provide a regionally important ecosystem service by suppressing a key soybean pest, reducing the need for insecticide applications. Furthermore, it suggests that management to maintain or enhance landscape diversity has the potential to stabilize or increase biocontrol services.

Ecology and Management of the Soybean Aphid in North America

The soybean aphid, Aphis glycines Matsumura, has become the single most important arthropod pest of soybeans in North America. Native to Asia, this invasive species was first discovered in North America in July 2000 and has rapidly spread throughout the northcentral United States, much of southeastern Canada, and the northeastern United States. In response, important elements of the ecology of the soybean aphid in North America have been elucidated, with economic thresholds, sampling plans, and chemical control recommendations widely adopted. Aphid-resistant soybean varieties were available to growers in 2010. The preexisting community of aphid natural enemies has been highly effective in suppressing aphid populations in many situations, and classical biological control efforts have focused on the addition of parasitoids of Asian origin. The keys to sustainable management of this pest include understanding linkages between the soybean aphid and other introduced and native species in a landscape context along with continued development of aphid-resistant varieties.

Increasing corn for biofuel production reduces biocontrol services in agricultural landscapes

Increased demand for corn grain as an ethanol feedstock is altering U.S. agricultural landscapes and the ecosystem services they provide. From 2006 to 2007, corn acreage increased 19% nationally, resulting in reduced crop diversity in many areas. Biological control of insects is an ecosystem service that is strongly influenced by local landscape structure. Here, we estimate the value of natural biological control of the soybean aphid, a major pest in agricultural landscapes, and the economic impacts of reduced biocontrol caused by increased corn production in 4 U.S. states (Iowa, Michigan, Minnesota, and Wisconsin). For producers who use an integrated pest management strategy including insecticides as needed, natural suppression of soybean aphid in soybean is worth an average of

Effect of Landscape Structure on Parasitoid Diversity and Parasitism in Agroecosystems

33 ha−1. At 2007–2008 prices these services are worth at least

Soybean Aphid Predators and Their Use in Integrated Pest Management

239 million y−1 in these 4 states. Recent biofuel-driven growth in corn planting results in lower landscape diversity, altering the supply of aphid natural enemies to soybean fields and reducing biocontrol services by 24%. This loss of biocontrol services cost soybean producers in these states an estimated

Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes

58 million y−1 in reduced yield and increased pesticide use. For producers who rely solely on biological control, the value of lost services is much greater. These findings from a single pest in 1 crop suggest that the value of biocontrol services to the U.S. economy may be underestimated. Furthermore, we suggest that development of cellulosic ethanol production processes that use a variety of feedstocks could foster increased diversity in agricultural landscapes and enhance arthropod-mediated ecosystem services.

An Inexpensive, Accurate Method for Measuring Leaf Area and Defoliation Through Digital Image Analysis

The armyworm (Pseudaletia unipuncta) was used as a model host insect to explore the influence of agricultural landscape structure at two spatial scales on larval parasitoid species richness and rates of larval parasitism in southern Michigan. First, within fields, we compared parasitoid communities in maize fields near, and distant from, a hedge- row edge. Second, we replicated these studies within a complex landscape (agricultural fields of small size embedded in a landscape with abundant hedgerows and woodlots) vs. a simple landscape (agricultural fields of large size embedded in a landscape with few hedgerows and woodlots). The structural differences between the simple and complex agricultural landscapes were characterized by analysis of aerial photographs and digital land-use data. After landscape analysis, three maize fields from each area were selected for the experimental studies. The complex landscape contained fields that were 75% smaller, had 63% more perimeter of wooded field edge per hectare of field area, and had 81% more field edge in wide hedgerow than fields in the simple landscape. Fields in the simple landscape had 74% and 53% more field edge in herbaceous roadside and crop-to-crop interfaces, respectively, than did fields in the complex landscape. In the six selected maize fields, third and fifth instar P. unipuncta were released indi- vidually onto maize plants 5 m and 90 m from a hedgerow edge. Larvae were recovered after 4-5 d and reared in the laboratory to record parasitoid emergence. Parasitoid species diversity was similar in both landscape types (simple landscape: four species; complex landscape: five species). Mean percentage parasitism was significantly higher in the complex landscape than in the simple landscape (13. 1% vs. 2.4%) but was not affected by the location within fields (near hedgerows vs. distant from hedgerows) in either landscape type.

Predators Suppress Aphis glycines Matsumura Population Growth in Soybean

Abstract The discovery of the soybean aphid, Aphis glycines Matsumura, in U.S. soybean production systems in 2000 has provided a unique opportunity to study the interaction of a new invader with existing natural enemy communities. One research thrust has been examining the role of predators in soybean aphid dynamics in the Midwest. We discuss the roles of predatory arthropods in field crops and set forth a conceptual model that we have followed to identify key predators in the soybean aphid system. We identify Orius insidiosus (Say) and Harmonia axyridis (Pallas) as potentially key predators and show our findings on their phenology in soybean fields and their impact on soybean aphid population dynamics. Finally, we discuss how this information can be used in integrated pest management programs for soybean aphid and point to gaps in our knowledge where future studies are needed.

Agricultural landscape simplification and insecticide use in the Midwestern United States

Significance Science-based polices are needed to inform sustainable bioenergy landscape design. Our key finding is that the linkage between biodiversity and ecosystem services is dependent not only on the choice of bioenergy crop but also on its location relative to other habitats. The implication is that careful design of bioenergy landscapes has the potential to enhance multiple services in food and energy crops, leading to important synergies that have not yet informed the ongoing bioenergy debate. This study is especially timely as high commodity prices are driving conversion of marginal lands to annual crop production, reducing future flexibility. Agriculture is being challenged to provide food, and increasingly fuel, for an expanding global population. Producing bioenergy crops on marginal lands—farmland suboptimal for food crops—could help meet energy goals while minimizing competition with food production. However, the ecological costs and benefits of growing bioenergy feedstocks—primarily annual grain crops—on marginal lands have been questioned. Here we show that perennial bioenergy crops provide an alternative to annual grains that increases biodiversity of multiple taxa and sustain a variety of ecosystem functions, promoting the creation of multifunctional agricultural landscapes. We found that switchgrass and prairie plantings harbored significantly greater plant, methanotrophic bacteria, arthropod, and bird diversity than maize. Although biomass production was greater in maize, all other ecosystem services, including methane consumption, pest suppression, pollination, and conservation of grassland birds, were higher in perennial grasslands. Moreover, we found that the linkage between biodiversity and ecosystem services is dependent not only on the choice of bioenergy crop but also on its location relative to other habitats, with local landscape context as important as crop choice in determining provision of some services. Our study suggests that bioenergy policy that supports coordinated land use can diversify agricultural landscapes and sustain multiple critical ecosystem services.

PREDATORS EXERT TOP‐DOWN CONTROL OF SOYBEAN APHID ACROSS A GRADIENT OF AGRICULTURAL MANAGEMENT SYSTEMS

Abstract We report a protocol using a common desk-top scanner and public domain software for measuring existing leaf area and leaf area removed as a result of herbivory. We compared the accuracy and precision of this method to that of a standard leaf area meter. Both methods were used to measure metal disks of a known area, the area of soybean (Glycine max L.) leaves, and the area removed by simulating leaf feeding with a hole-punch. We varied the amount of injury across a low, medium, and high degree of simulated feeding. The mean area of 10 cm2 and 50 cm2 metal disks was more accurately estimated with the leaf area meter than the desk-top scanner. Leaf area estimates from both methods were highly correlated. The desk-top scanner accurately estimated the leaf area removed from the low, medium, or high degree of simulated leaf feeding. However, the leaf area meter overestimated low levels of simulated feeding injury. Though measuring a leaf’s surface area with a desk-top scanner requires two steps (creating a digital image file and calculating the area represented by that image), the overall time required to measure leaf injury is shorter than with a leaf area meter. This relatively simple and inexpensive method of estimating leaf area and feeding damage has advantages in certain experimental situations where a prefeeding measurement of the leaf is impossible or undesirable, or when small amounts of feeding occur.