The role of ants in north temperate grasslands: a review.

Historic and current land-use changes have altered the landscape for grassland biota, with over 90% of grasslands and savannas converted to agriculture or some other use in north temperate regions. Reintegrating grasslands into agricultural landscapes can increase biodiversity while also providing valuable ecosystem services. In contrast to their well-known importance in tropical and subtropical ecosystems, the role of ants in temperate grasslands is often underappreciated. As consumers and ecosystem engineers, ants in temperate grasslands influence invertebrate, plant, and soil microbial diversity and potentially alter grassland productivity. As common and numerically dominant invertebrates in grasslands, ants can also serve as important indicator species to monitor conservation and management practices. Drawing on examples largely from mesic, north temperate studies, and from other temperate regions where necessary, we review the roles of ants as consumers and ecosystem engineers in grasslands. We also identify five avenues for future research to improve our understanding of the roles of ants in grasslands. This includes identifying how grassland fragmentation may influence ant community assembly, quantifying how ant communities impact ecosystem functions and soil processes, and understanding how ant communities and their associated interactions are impacted by climate change. In synthesizing the role of ants in temperate grasslands and identifying knowledge gaps, we hope this and future work will help inform how land managers maximize grassland conservation value while increasing multiple ecosystem services and minimizing disservices.

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 Simpson's 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.

Establishing next-generation pest control services in rice fields: eco-agriculture.

Pesticides are commonly used in food crop production systems to control crop pests and diseases and ensure maximum yield with high market value. However, the accumulation of these chemical inputs in crop fields increases risks to biodiversity and human health. In addition, people are increasingly seeking foods in which pesticide residues are low or absent and that have been produced in a sustainable fashion. More than half of the world's human population is dependent on rice as a staple food and chemical pesticides to control pests is the dominant paradigm in rice production. In contrast, the use of natural enemies to suppress crop pests has the potential to reduce chemical pesticide inputs in rice production systems. Currently, predators and parasitoids often do not persist in rice production landscapes due to the absence of shelter or nutritional sources. In this study, we modified the existing rice landscape through an eco-engineering technique that aims to increase natural biocontrol agents for crop protection. In this system, planting nectar-rich flowering plants on rice bunds provides food and shelter to enhance biocontrol agent activity and reduce pest numbers, while maintaining grain yield. The abundance of predators and parasitoids and parasitism rates increased significantly in the eco-engineering plots compared to the insecticide-treated and control plots. Moreover, a significantly lower number of principal insect pests and damage symptoms were found in treatments where flowering plants were grown on bunds than in plots where such plants were not grown. This study indicates that manipulating habitat for natural enemies in rice landscapes enhances pest suppression and maintains equal yields while reducing the need for insecticide use in crop fields.

Attractiveness of Michigan native plants to arthropod natural enemies and herbivores.

The use of plants to provide nectar and pollen resources to natural enemies through habitat management is a growing focus of conservation biological control. Current guidelines frequently recommend use of annual plants exotic to the management area, but native perennial plants are likely to provide similar resources and may have several advantages over exotics. We compared a set of 43 native Michigan perennial plants and 5 frequently recommended exotic annual plants for their attractiveness to natural enemies and herbivores for 2 yr. Plant species differed significantly in their attractiveness to natural enemies. In year 1, the exotic annual plants outperformed many of the newly established native perennial plants. In year 2, however, many native perennial plants attracted higher numbers of natural enemies than exotic plants. In year 2, we compared each flowering plant against the background vegetation (grass) for their attractiveness to natural enemies and herbivores. Screening individual plant species allowed rapid assessment of attractiveness to natural enemies. We identified 24 native perennial plants that attracted high numbers of natural enemies with promise for habitat management. Among the most attractive are Eupatorium perfoliatum L., Monarda punctata L., Silphium perfoliatum L., Potentilla fruticosa auct. non L., Coreopsis lanceolata L., Spiraea alba Duroi, Agastache nepetoides (L.) Kuntze, Anemone canadensis L., and Angelica atropurpurea L. Subsets of these plants can now be tested to develop a community of native plant species that attracts diverse natural enemy taxa and provides nectar and pollen throughout the growing season.

Plant characteristics associated with natural enemy abundance at Michigan native plants.

Habitat management is a type of conservation biological control that focuses on increasing natural enemy populations by providing them with plant resources such as pollen and nectar. Insects are known to respond to a variety of plant characteristics in their search for plant-provided resources. A better understanding of the specific characteristics used by natural enemy insects in selecting these resources could greatly improve efficiency in screening plants for habitat management. We examined 5 previously tested and widely recommended resource plants and 43 candidate plants to test whether the number and type of natural enemies and herbivores at each plant were predicted by plant characteristics including: period of peak bloom, floral area, maximum flower height, hue, chroma, and corolla size. Natural enemy abundance increased with week of peak bloom and greater floral area across all plants tested. Ordination of plant characteristics indicated that increasing floral area, period of peak bloom, maximum flower height, and decreasing corolla width grouped together into a single principal component. Both natural enemy and herbivore abundance increased significantly with the principal component for this set of characteristics, but the relationship with herbivore abundance was weaker. These results indicate that, for a given time of the season, selection of plants with the largest floral area has potential to increase natural enemy abundance in habitat management plantings and streamline plant selection for habitat management.

The multiple Coulomb scattering of very heavy charged particles.

An experiment was performed at the Lawrence Berkeley Laboratory BEVALAC to measure the multiple Coulomb scattering of 650-MeV/A uranium nuclei in 0.19 radiation lengths of a Cu target. Differential distributions in the projected multiple scattering angle were measured in the vertical and horizontal planes using silicon position-sensitive detectors to determine particle trajectories before and after target scattering. The results were compared with the multiple Coulomb scattering theories of Fermi and Molière, and with a modification of the Fermi theory, using a Monte Carlo simulation. These theories were in excellent agreement with experiment at the 2 sigma level. The best quantitative agreement is obtained with the Gaussian distribution predicted by the modified Fermi theory.

Habitat management to conserve natural enemies of arthropod pests in agriculture.

Many agroecosystems are unfavorable environments for natural enemies due to high levels of disturbance. Habitat management, a form of conservation biological control, is an ecologically based approach aimed at favoring natural enemies and enhancing biological control in agricultural systems. The goal of habitat management is to create a suitable ecological infrastructure within the agricultural landscape to provide resources such as food for adult natural enemies, alternative prey or hosts, and shelter from adverse conditions. These resources must be integrated into the landscape in a way that is spatially and temporally favorable to natural enemies and practical for producers to implement. The rapidly expanding literature on habitat management is reviewed with attention to practices for favoring predators and parasitoids, implementation of habitat management, and the contributions of modeling and ecological theory to this developing area of conservation biological control. The potential to integrate the goals of habitat management for natural enemies and nature conservation is discussed.

Fiber-optic-graded-index-lens absorbance sensor with wavelength-scanning capability.

A single optical-fiber absorbance sensor that contains a graded-index lens is described. The sensor can be tailored for a desired broad wavelength region, path length, and size. Laboratory evaluations of sensors of varying sizes and path lengths are presented. The sensors, even without the added expense of optical coatings, report true absorbance spectra for the 420-850-nm wavelength region with a linear response over a wide absorbance range. Direct comparison with several other sensor configurations shows that the graded-index-lens-based sensor has a high optical efficiency. Potential applications of the sensor include absorbance measurements at hazardous or remote sites and in vivo medical applications.