Natural Enemy Ecology Research Articles

Insectivorous bats in Indian rice fields respond to moonlight, temperature, and insect activity

ContextRice, India’s most widely grown crop, suffers substantial and increasing yield loss to insect pests. Insectivorous bats are known suppressors of insect pests, providing significant economic value to agricultural systems worldwide, yet their ecology in Indian agricultural landscapes is poorly understood.ObjectivesWe assess the influence of key biotic and abiotic factors on the activity of insectivorous bats over the growing season and within a night in a rice cultivation landscape.MethodsPassive acoustic recorders were used to track bat activity in a rice field in the Sonitpur district of Assam, India. We used generalised linear mixed models to analyse the effect of temperature, insect activity, and moonlight intensity on the activity of six bat sonotypes. We also used a multimodal analysis to describe the within-night activity patterns of these sonotypes.ResultsMinimum nightly temperature and moonlight intensity had a positive and negative influence, respectively, on the activity of six bat sonotypes, while the activity of four bat sonotypes increased with insect activity. Within-night activity showed one of two patterns: three sonotypes displayed a dusk peak in activity, while the three other sonotypes were active through the night.ConclusionThe potential to maximise natural pest control in agricultural landscapes can only be realised through understanding the ecology of natural enemies in these landscapes. Our findings suggest that bats in rice fields are tracking insects over a season and within a night, pointing to a valuable ecosystem service in Indian agriculture that is yet to be quantified.

Pathogens and predators: examining the separate and combined effects of natural enemies on assemblage structure.

Natural enemy ecology strives to unify predator-prey and host-pathogen interactions under a common framework to gain insights into community- and ecosystem-level processes. To address this goal, ecologists need a greater emphasis on: (1) quantifying pathogen-mediated effects on community structure to enable comparisons with predator-mediated effects and (2) determining the interactive effects of combined natural enemies on communities. We conducted a mesocosm experiment to assess the individual and combined effects of predators (dragonfly larvae and adult water bugs) and a pathogen (ranavirus) on the abundance and composition of a larval amphibian assemblage. We found that our three natural enemies structured victim assemblages in unique ways, producing distinct assemblages. Additionally, we found that in combination treatments, predators mainly drove assemblage structure such that the assemblages most closely resembled their respective predator treatments. We also found that predators reduced infection prevalence in combination treatments, and that the magnitude of this effect was dependent on predator identity. Compared to virus-alone treatments, the presence of dragonflies and water bugs reduced infection prevalence by 79% and 63%, respectively. Additionally, the presence of dragonflies eliminated ranavirus infection in two species, which demonstrates the prominent role of predators in disease dynamics in this system. Overall, this work demonstrates the importance of considering natural enemies in community ecology, as each enemy can elicit a unique structural change. Additionally, this study provides a unique empirical test of the healthy herds hypothesis for multi-species assemblages and underscores the importance of advancing our understanding of multi-enemy interactions within communities.

Bioefficacy, environmental safety and synergistic impacts of biorational formulations against whitefly, leafhopper and blister beetle in organic okra ecosystem

AbstractWhitefly (Bemisia tabaci Gennadius), leafhopper (Amrasca biguttula biguttula Ishida) and large yellow-banded blister beetle (Mylabris phalerata) cause considerable damage to okra, especially under organic farming. Thus, the present study was carried out to test the bioefficacy and environmental safety of six naturally derived components [indigenous water plant extracts, i.e. chilli (Capsicum annum), garlic (Allium sativum L.) and neem (Azadirachta indica A. Juss.) along with cow urine in three different combinations, one commercial botanical (azadirachtin 0.15%), and two formulated entomopathogenic fungi (Verticillium lecanii and Beauveria bassiana)] on aforesaid pests for two consecutive years at field scale. In addition to this, the eco-toxicological effect of naturally derived components was also studied on natural enemies’ populations, viz. spiders and coccinellids. Quaternary mixture application of chilli, garlic, neem leaf and cow urine (CGNC) at 10% w/v was found effective in reducing leafhoppers (94.6%), whiteflies (95.2%) and blister beetle (94.6%) over control. Okra treated with CGNC produced a higher marketable fruit yield (18.44 mg/ha) than those of other treatments. It was also observed that the application of CGNC had no phytotoxic symptoms on okra plants. Application of CGNC was found safer to the natural enemy's population (spiders and coccinellids). Thus, the study suggests that CGNC can be considered as a potential source for managing the population of whitefly, leafhopper and blister beetle without affecting the ecology of natural enemies and it could be a viable eco-friendly option in organic okra production for ensuring food safety and healthy environment.

Risk-Induced Trait Responses and Non-consumptive Effects in Plants and Animals in Response to Their Invertebrate Herbivore and Parasite Natural Enemies

Predators kill and consume prey, but also scare living prey. Fitness of prey can be reduced by direct killing and consumption, but also by non-consumptive effects (NCEs) if prey show costly risk-induced trait responses (RITRs) to predators, which are meant to reduce predation risk. Recently, similarities between predators and parasites as natural enemies have been recognized, including their potential to cause victim RITRs and NCEs. However, plant-herbivore and animal host-parasite associations might be more comparable as victim-enemy systems in this context than either is to prey-predator systems. This is because plant herbivores and animal parasites are often invertebrate species that are typically smaller than their victims, generally cause lower lethality, and allow for further defensive responses by victims after consumption begins. Invertebrate herbivores can cause diverse RITRs in plants through various means, and animals also exhibit assorted RITRs to increased parasitism risk. This synthesis aims to broadly compare these two enemy-victim systems by highlighting the ways in which plants and animals perceive threat and respond with a range of induced victim trait responses that can provide pre-emptive defense against invertebrate enemies. We also review evidence that RITRs are costly in terms of reducing victim fitness or abundance, demonstrating how work with one victim-enemy system can inform the other with respect to the frequency and magnitude of RITRs and possible NCEs. We particularly highlight gaps in our knowledge about plant and animal host responses to their invertebrate enemies that may guide directions for future research. Comparing how potential plant and animal victims respond pre-emptively to the threat of consumptionviaRITRs will help to advance our understanding of natural enemy ecology and may have utility for pest and disease control.

Only Females Oviposit: Chemical Discrimination of Adult Stink Bug Sex by the Egg Parasitoid Trissolcus japonicus

Egg parasitoids foraging for suitable hosts scattered in the environment rely mainly on chemical cues. Elucidating the chemical ecology of natural enemies is important in the development of effective and successful strategies for conservation biological control. In this context, the host cuticular hydrocarbons, which are exploited by several species of egg parasitoids as contact kairomones, could be used to retain them by providing information about the presence and the sex of adults of the target species: sex is important because only females of the host species lay the eggs that can be subsequently utilized for parasitoid reproduction. However, the chemical basis of host sex discrimination in egg parasitoids is not well understood. We carried out behavioral and chemical bioassays to investigate the role played by contact chemical cues left by adults of the brown marmorated stink bug, Halyomorpha halys Stål, in host egg searching behavior and adult host sex discrimination by the egg parasitoid Trissolcus japonicus (Ashmead). A first set of bioassays showed that parasitoids spent more time exploring patches contaminated with chemicals associated with adult H. halys females compared with adult males. Similar responses were displayed by T. japonicus when hexane extracts of H. halys were tested suggesting that non-polar chemical compounds are involved in host sex discrimination. GC-MS analysis of hexane extracts revealed quantitative differences in the cuticular compounds of the two sexes, with 1-hexadecene (more abundant in males) being the most important component in determining these differences. Hexane extracts of H. halys females blended with synthetic 1-hexadecene significantly reduced the wasps’ arrestment responses compared to crude extracts.

Bugs scaring bugs: enemy-risk effects in biological control systems.

Enemy‐risk effects, often referred to as non‐consumptive effects (NCEs), are an important feature of predator–prey ecology, but their significance has had little impact on the conceptual underpinning or practice of biological control. We provide an overview of enemy‐risk effects in predator–prey interactions, discuss ways in which risk effects may impact biocontrol programs and suggest avenues for further integration of natural enemy ecology and integrated pest management. Enemy‐risk effects can have important influences on different stages of biological control programs, including natural enemy selection, efficacy testing and quantification of non‐target impacts. Enemy‐risk effects can also shape the interactions of biological control with other pest management practices. Biocontrol systems also provide community ecologists with some of the richest examples of behaviourally mediated trophic cascades and demonstrations of how enemy‐risk effects play out among species with no shared evolutionary history, important topics for invasion biology and conservation. We conclude that the longstanding use of ecological theory by biocontrol practitioners should be expanded to incorporate enemy‐risk effects, and that community ecologists will find many opportunities to study enemy‐risk effects in biocontrol settings.

Approaches to Identify the Value of Seminatural Habitats for Conservation Biological Control.

Invertebrates perform many vital functions in agricultural production, but many taxa are in decline, including pest natural enemies. Action is needed to increase their abundance if more sustainable agricultural systems are to be achieved. Conservation biological control (CBC) is a key component of integrated pest management yet has failed to be widely adopted in mainstream agriculture. Approaches to improving conservation biological control have been largely ad hoc. Two approaches are described to improve this process, one based upon pest natural enemy ecology and resource provision while the other focusses on the ecosystem service delivery using the QuESSA (Quantification of Ecological Services for Sustainable Agriculture) project as an example. In this project, a predictive scoring system was developed to show the potential of five seminatural habitat categories to provide biological control, from which predictive maps were generated for Europe. Actual biological control was measured in a series of case studies using sentinel systems (insect or seed prey), trade-offs between ecosystem services were explored, and heatmaps of biological control were generated. The overall conclusion from the QuESSA project was that results were context specific, indicating that more targeted approaches to CBC are needed. This may include designing new habitats or modifying existing habitats to support the types of natural enemies required for specific crops or pests.

Improving the efficiency of augmentative biological control with arthropod natural enemies: A modeling approach

A better understanding of the life-history traits of biocontrol agents and their effect on population dynamics is key to obtaining more efficient pest control and generating higher economic returns for biocontrol practitioners. To this end, we constructed an optimality simulation model based on principles of the behavioral ecology of natural enemies. This model allows for the identification of the most important life-history traits of natural enemies (e.g., fecundity, longevity, attack rate, competition and dispersal), taking into account the costs and benefits for biocontrol practitioners. The model was kept general and was designed in such a way that it can be adapted to different target species and their specific ecology (natural enemy-pest-plant combination). Results indicate strong interactions between the optimized life-history traits of the biocontrol agents. Two different optimized life-history strategies for the agents were found with higher potential economic returns. These strategies differ most significantly in the plant-leaving decision and host handling time of the biocontrol agent, but also in their respective fecundity, longevity and dispersal ability. The preferred strategy depends on the number of agents released and the growth rate of the plant. Information from these optimality models can help to determine which agents should be released and how they should be released in a specific agro-ecological situation.

Of poisons and parasites-the defensive role of tetrodotoxin against infections in newts.

Classical research on animal toxicity has focused on the role of toxins in protection against predators, but recent studies suggest these same compounds can offer a powerful defense against parasites and infectious diseases. Newts in the genus Taricha are brightly coloured and contain the potent neurotoxin, tetrodotoxin (TTX), which is hypothesized to have evolved as a defense against vertebrate predators such as garter snakes. However, newt populations often vary dramatically in toxicity, which is only partially explained by predation pressure. The primary aim of this study was to evaluate the relationships between TTX concentration and infection by parasites. By systematically assessing micro- and macroparasite infections among 345 adult newts (sympatric populations of Taricha granulosa and T.torosa), we detected 18 unique taxa of helminths, fungi, viruses and protozoans. For both newt species, per-host concentrations of TTX, which varied from undetectable to >60μg/cm2 skin, negatively predicted overall parasite richness as well as the likelihood of infection by the chytrid fungus, Batrachochytrium dendrobatidis, and ranavirus. No such effect was found on infection load among infected hosts. Despite commonly occurring at the same wetlands, T.torosa supported higher parasite richness and average infection load than T.granulosa. Host body size and sex (females > males) tended to positively predict infection levels in both species. For hosts in which we quantified leucocyte profiles, total white blood cell count correlated positively with both parasite richness and total infection load. By coupling data on host toxicity and infection by a broad range of micro- and macroparasites, these results suggest that-alongside its effects on predators-tetrodotoxin may help protect newts against parasitic infections, highlighting the importance of integrative research on animal chemistry, immunological defenses and natural enemy ecology.

The Life History of Chelymorpha alternans (Coleoptera: Chrysomelidae: Cassidinae) in Panamá

Here we describe an investigation of the life history characteristics, behavior, immature and adult morphologies of the Neotropical tortoise beetle Chelymorpha alternans (Boheman; Coleoptera: Chrysomelidae: Cassidinae) from the Republic of Panama. Developmental times and behavioral characteristics for individuals maintained under laboratory and field conditions are evaluated. Survival rates of individuals maintained under field and laboratory conditions are compared. A list of convolvulaceous host plants utilized by C. alternans is provided. Empirical studies investigating the biology of C. alternans are reviewed. This study contributes to our knowledge of quantitative and qualitative aspects of this lspecies' biology. These findings demonstrate that C. alternans is an organism that develops, behaves, and interacts with host plants, much as other tortoise beetles do. Rigorous, multi-year investigation of this ecologically representative species has produced a comparative life history description that expands our knowledge of general Cassidinae and Coleoptera biology. The natural history background, life history descriptions, diet breadth information, and literature review provided in this contribution make a compelling case for continued utilization of C. alternans as a representative tortoise beetle species for a variety of field and laboratory based studies in plant–insect interactions, chemical ecology, natural enemy ecology, and phenotypic trait and diet breadth evolution.

Time-lagged effect of predators on tadpole behaviour and parasite infection.

Prey should adjust their defences against natural enemies to match their current level of risk and balance other needs. This is particularly important when optimal defences represent trade-offs, as is the case with many predator-induced trait-mediated indirect effects (TMIEs) that are antagonistic to those promoting host resistance to parasites and pathogens. However, trade-offs may depend on whether different natural enemies are present simultaneously or represent temporally discrete threats. We found that larval amphibians (Anaxyrus americanus) previously exposed to predator cues did not engage in anti-parasite behaviours (activity increases) in response to a current risk of infection by a pathogenic trematode parasite compared to controls, resulting in higher infection intensities. This suggests that the memory of the likely more lethal threat (predation) had greater influence, maladaptively dampening tadpole activity. Incorporating complexity inherent in natural systems, including spatial and temporal overlap, is necessary to better understand natural enemy ecology and how TMIEs relate to infectious diseases.

Introduction to the Symposium: Parasites and Pests in Motion: Biology, Biodiversity and Climate Change.

Although climate change can cause extreme alterations to ecosystems, only limited research has investigated how altered physical conditions (e.g., warming, extreme temperature events, sea level rise, ocean acidification, and altered precipitation) influence species interactions. In particular, the interplay between host and parasites in such a changing world is in need of study. Our objective in organizing this symposium was to bring together researchers working on a wide variety of natural enemies (parasites, pathogens, and pests), to exchange knowledge on how aspects of global climate change may alter the distribution and ecology of these organisms and their hosts. It is our intention that the symposium and the resulting articles will foster more accurate modeling of and predictions about the impacts of climate change on the biology and ecology of natural enemies and their hosts.

Natural enemy ecology: comparing the effects of predation risk, infection risk and disease on host behaviour

SummaryGrowing interest in unifying the field of natural enemy ecology has revealed similarities between predation and parasitism. In parallel with predation, parasite infection – and even the threat of infection – can alter host traits and indirectly affect community interactions. Nonetheless, few studies have considered multiple mechanisms of natural enemy‐induced behavioural alteration in parallel (e.g. effects before and after enemy contact) or the factors that drive variation in behavioural responses.We first evaluated how the threat of infection by a virulent trematode (Ribeiroia ondatrae) compared to the well studied risk of predation in triggering inducible defences in amphibian hosts, prior to direct contact with either enemy. We then evaluated five separate factors that influenced the magnitude of parasite‐induced behavioural changes after successful transmission.In both the laboratory and an outdoor mesocosm experiment, we found no evidence that tadpoles of two species (Pseudacris regillaandAnaxyrus boreas) altered their activity levels in response to chemical cues from uninfected host snails, trematode‐infected snails, or from conspecifics actively becoming infected. In contrast, tadpoles sharply reduced their activity in response to lethal predation risks posed by caged dragonfly larvae.After infection, however,Ribeiroiacaused strong decreases in host activity and escape distance that correlated positively with infection intensity and negatively with host size and developmental stage. Five days after infection with a one‐time pulse exposure, hosts recovered to near‐normal activity levels. Hosts exposed to a chronic daily exposure of equal intensity, however, continued to decrease activity. UnlikeRibeiroia, two less virulent trematodes had no detectable effects on host behaviour.Our results highlight key distinctions between predation and parasitism. The contrasting effects prior to enemy contact may stem from the fact that unlike predation, the consequences of macroparasite infection are intensity‐dependent and unpredictable. In contrast, the strong changes in host behaviour after infection are more similar to non‐consumptive predator effects in terms of their potential influences on host fitness and community interactions.

Predation and disease: understanding the effects of predators at several trophic levels on pathogen transmission

Summary Predators can directly and indirectly influence host–parasite interactions by consuming infected individuals, by removing infectious parasite stages and by changing host traits (e.g. behaviour). Because such effects can affect infection positively or negatively, understanding the net effects of predation on pathogen transmission under natural conditions is important. We conducted a mesocosm experiment to examine the effects of predators on interactions between tadpole hosts (Pseudacris regilla) and trematode parasites (Ribeiroia ondatrae). We manipulated the presence of (non‐lethal, i.e., caged) predators of tadpoles (dragonfly larvae) and (potentially lethal) parasite predators (damselfly larvae) to evaluate their individual and combined effects on host infection. We expected that dragonflies would reduce tadpole activity and thereby increase parasite infection through a reduction in antiparasite behaviour. Because damselflies can consume parasites in the laboratory, we predicted that damselflies would lower infection by consuming parasites before they infected tadpoles. Our goal was to evaluate the net consequences of these predator‐mediated effects for host/prey infection. The presence of caged dragonflies reduced tadpole activity, resulting in a ˜50% increase in average infection load compared to treatments without predators. In contrast to our prediction that damselflies would reduce infection, damselflies elicited behavioural and morphological changes in hosts similar to dragonflies, with a comparable increase in parasite transmission. Thus, predator‐mediated effects were evident predominantly through changes in host/prey behaviour, rather than through changes in the abundance of parasites. The lack of a direct effect of predators on infection (i.e. via consumption of parasites) could be the result of the presence of alternative prey (zooplankton) or a mismatch in timing between visual predators feeding during the day and parasites released from the first intermediate host and infecting amphibians at night. The presence of predators also stimulated morphological defences in their tadpole prey, including increased tail and body depth. Interestingly, we found that parasite infection also induced morphological changes in tadpole tail and body depth, similar to changes produced by (non‐lethal) cues from predators. Parasites caused malformations in tadpoles, but there were no effects on tadpole growth or development from either parasites or predators. This research has key implications for linking predation and infectious disease in aquatic ecosystems. Our results emphasise the importance of indirect effects of predators on infection and highlight possible trade‐offs in mitigating the concurrent risks of predation and disease. Parasites can also alter host morphology through trait‐mediated effects similar to predators, supporting a broader inclusion of parasites in the study of the ecology of natural enemies.

Lack of genetic differentiation between contrasted overwintering strategies of a major pest predator Episyrphus balteatus (Diptera: Syrphidae): implications for biocontrol.

Winter ecology of natural enemies has a great influence on the level and efficiency of biological control at spring. The hoverfly Episyrphus balteatus (DeGeer) (Diptera: Syrphidae) is one of the most important natural predators of crop aphids in Europe. Three different overwintering strategies coexist in this species which makes it a good model in order to study ecologically-based speciation processes. The purpose of this study was to determine whether E. balteatus populations with alternative overwintering strategies are genetically differentiated. To that aim, we developed 12 specific microsatellite markers and evaluated the level of neutral genetic differentiation between E. balteatus field populations that overwinter in the three different ways described in this species (i.e. migration, local overwintering at a pre-imaginal stage, and local overwintering at adult stage). Results showed a lack of neutral genetic differentiation between individuals with different overwintering strategies although there are strong ecological differences between them. All pair-wise FST values are below 0.025 and non-significant, and Bayesian clustering showed K = 1 was the most likely number of genetic clusters throughout our sample. The three overwintering strategies form one unique panmictic population. This suggests that all the individuals may have genetic material for the expression of different overwintering phenotypes, and that their commitment in one particular overwintering strategy may depend on environmental and individual factors. Consequently, the prevalence of the different overwintering strategies would be potentially modified by landscape engineering and habitat management which could have major implications for biological control.

Toward a General Theory for How Climate Change Will Affect Infectious Disease

Toward a General Theory for How Climate Change Will Affect Infectious Disease

Chemical ecology and conservation biological control

Elucidating the chemical ecology of natural enemies, herbivores and host plants is important in the development of effective and successful integrated pest management (IPM) strategies where abundance and distribution of natural enemies could be manipulated by semiochemicals for improved conservation biological control (CBC). In response to attack by herbivores, plants produce semiochemicals called Herbivore-Induced Plant Volatiles (HIPVs) which act to repel pests and attract their natural enemies. Damaged, and in some cases, intact plants may also produce volatile signals that warn other plants of impending attack. Some of these intact plants are used as intercrops in ‘push–pull’ strategies; cropping systems based on stimulo-deterrent principle, where the target crop is intercropped with herbivore repellent plants (push) while attractant plants (pull) are planted around this intercrop. The intercrop, in addition to repelling the herbivores, attracts and conserves natural enemies thereby ensuring continued suppression of the pests. This natural delivery of semiochemicals for CBC is currently being exploited by smallholder farmers in eastern Africa in the management of cereal stemborers in maize and sorghum. Synthetic HIPVs also have the potential to effectively recruit natural enemies, thereby improving CBC as has been demonstrated in a series of field experiments in vineyards and hop yards in the Pacific Northwest of the United States. Potentially, plants could be ‘turned on’ by synthetic HIPV signals, and therefore become sources of natural enemy-recruiting volatiles. With the rapid development of plant molecular biology, modification of secondary plant metabolism is also possible which could allow appropriate semiochemicals to be generated by plants at certain growth stages. By identifying the promoter sequences associated with external plant signals that induce biochemical pathways, plant defense genes could be ‘switched on’ prior to insect attack. We review recent research on ‘push–pull’ strategies and synthetic HIPVs in recruitment of beneficial arthropods and warding off pest attack.

The population consequences of natural enemy enhancement, and implications for conservation biological control

AbstractWe explore models for the management of invertebrate pests by enhancing the efficacy or local abundance of existing natural enemies. Different aspects of natural enemy biology had different effects on prey density. Enhancement of enemy search rate or prey conversion efficiency showed the greatest potential for reducing prey density, while maximum consumption rate by predators, and parasitoid fecundity, had less effect. The effect on prey density of increased natural enemy longevity depended on its interaction with other parameters. The degree of manipulation needed to achieve a given reduction in prey populations was largely determined by the enemy's potential reproductive rate. Spatial ‘‘attraction’’ of enemies to a target site had an almost linear effect on local prey density. We conclude that successful conservation biological control benefits from a directed approach, targeting the most important aspects of natural enemy ecology, and that there is considerable potential for further research in this area.

Higher-order predators and the regulation of insect herbivore populations.

Empirical research has not supported the prediction that populations of terrestrial herbivorous arthropods are regulated solely by their natural enemies. Instead, both natural enemies (top-down effects) and resources (bottom-up effects) may play important regulatory roles. This review evaluates the hypothesis that higher-order predators may constrain the top-down control of herbivore populations. Natural enemies of herbivorous arthropods generally are not top predators within terrestrial food webs. Insect pathogens and entomopathogenic nematodes inhabiting the soil may be attacked by diverse micro- and mesofauna. Predatory and parasitic insects are attacked by their own suite of predators, parasitoids, and pathogens. The view of natural enemy ecology that has emerged from laboratory studies, where natural enemies are often isolated from all elements of the biotic community except for their hosts or prey, may be an unreliable guide to field dynamics. Experimental work suggests that interactions of biological control agents with their own natural enemies can disrupt the effective control of herbivore populations. Disruption has been observed experimentally in interactions of bacteria with bacteriophages, nematodes with nematophagous fungi, parasitoids with predators, parasitoids with hyperparasitoids, and predators with other predators. Higher-order predators have been little studied; manipulative field experiments will be especially valuable in furthering our understanding of their roles in arthropod communities.

Biodiversity and pest management in agroecosystems

* Preface to the Second Edition * Acknowledgments * Introduction * Chapter 1. The Ecological Role of Biodiversity in Agriculture * Traditional Agroecosystems As Models of Biodiverse Farms * The Ecological Role of Biodiversity * The Nature of Biodiversity in Agroecosystems * Chapter 2. Agroecology and Pest Management * The Nature of Agricultural Habitats and its Relation to Pest Buildup * Crop Diversification and Biological Control * Chapter 3. Plant Diversity and Insect Stability in Agroecosystems * Ecological Theory * Theory Dilemmas * Chapter 4. Insect Manipulation Through Weed Management * Weeds As Sources of Insect Pests in Agroecosystems * The Role of Weeds in the Ecology of Natural Enemies * Insect Dynamics in Weed-Diversified Crop Systems * Isolating the Ecological Effects of Weed Diversity * Crop-Weed Management Considerations * Chapter 5. Insect Management in Multiple-Cropping Systems * Patterns of Insect Abundance in Polycultures * Herbivore Trends in Polycultures * Case Study 1: Maize Intercrops and Pest Attack * Case Study 2: Cassava Intercrops and Pest Incidence * Case Study 3: Reducing Stemborers in Africa * Living Mulches: A Special Type of Intercrop * Methodologies to Study Insect Dynamics in Polycultures * Management Considerations * Chapter 6. Insect Ecology in Orchards Under Cover-Crop Management * Selecting and Managing Cover Crops in Orchards * Case Study 1: Apple Orchards in California * Case Study 2: Pecan Orchards in Georgia * Case Study 3: Summer Cover Crops in Vineyards * Chapter 7. The Influence of Adjacent Habitats on Insect Populations in Crop Fields * Crop Edges and Insect Pests * Field Boundaries and Natural Enemies * Designing and Managing Borders * Case Study 1: Exchange of Arthropods at the Interface of Apple Orchards and Adjacent Woodlands * Manipulating Crop-Field Border Vegetation * Case Study 2: Biological Corridors in Vineyards * Case Study 3: Strip Management to Augment Predators * Chapter 8. The Dynamics of Insect Pests in Agroforestry Systems * The Effects of Trees in Agroforestry on Insect Pests * Designing Natural Successional Analog Agroforestry Systems * The Need for Further Research * Chapter 9. Designing Pest-Stable Vegetationally Diverse Agroecosystems * Monocultures and the Failure of Conventional Pest-Control Approaches * Towards Sustainable Agriculture * Requirements of Sustainable Agroecosystems * Designing Healthy Agroecosystems * Healthy Soils--Healthy Plants * Restoring Diversity in Agricultural Systems * Enhancing Surrounding Biodiversity * Case Study 1: Diversification of an Onion Agroecosystem in Michigan * Case Study 2: A Diversified Small Farming System in Chile * Conclusion * References * Index