Theory and Practice of the Cropping Systems Approach to Reducing Nematode Problems in the Tropics

Plant-parasitic nematodes are major constraints to the productivity of tropical farming operations. Intensive land use and climatic conditions favorable to nematode development contribute to increased crop losses due to these pests. Many farmers in developing tropical countries have limited resources and management options. Cropping systems research is a relatively low-cost, low-input method of optimizing existing agricultural practices with respect to limiting losses due to plant-parasitic nematodes. Specific tropical farming practices are discussed along with problems they pose for research in quantitative hematology. Comprehensive, systematic research methods for delineating and using nematode-host relationships are described, and new ways of dealing with complex multicropping systems are suggested.     

Management of Heterodera glycines by Cropping and Cultural Practices

Heterodera glycines was identified in North Carolina in 1954, although symptoms of the disease were noted in the state at least 8 years earlier. Crop rotation experiments designed to develop management systems were initiated in 1956. Two or more years in production of a nonhost crop resulted in decreases of the nematode to low or undetectable levels with acceptable subsequent yields of soybean (Glycine max). Because of almost complete dependence on resistant cultivars and (or) nematicides for nematode control, crop rotation experiments were not conducted from 1962 to 1980. Research on control of H. glycines, beginning in 1981, emphasized biological and ecological aspects of the nematode in order to determine cropping systems that restrict the nematode to nondamaging levels. Mortality during embryogenesis was high at temperatures above 30 C. Hatching of eggs occurs readily in May and June. Postinfection development takes 2-3 weeks at weekly mean temperatures of 22-29 C and is slow above and below those temperatures. Egg production is high during the late growing season. Some cultural practices such as planting early maturing cultivars in mid-to-late June and rotation with a nonhost effectively keeps populations at low levels.     

Control of gastrointestinal strongyles in goats

Gastrointestinal (GI) parasitism are the most serious problem affecting sheep and goats worldwide. Economic losses caused by GI strongyles are related to decreased production, costs for treatment and prophylaxis and animal death. Effective control of internal parasites in small ruminants is one of the most difficult challenges encountered by veterinary in practice. For control of helminth parasites in grazing animals it is important knowledge of epidemiology of the parasite as it interacts with the host in a specific climatic, management and production environment. Sheep and goats are infected by many of the same GI nematodes, but feeding and management practices alter levels of parasitism between the two ruminants. The most commonly anthelmintics used for helminth control in small ruminants include three chemical groups: Imidazothiazoles/Pyrimidines (Im/Pm), Benzimidazoles/Probenzimidazoles (Bz/Pbz) and Macrocyclic Lactones (ML). The control of gastrointestinal strongyles infections in goats shows specific patterns. The use of anthelmintics in goats is based upon anthelmintics goats-suited dose rates taking into account the specific pharmacokinetics features of some anthelmintics in this species. Several types of control strategies: deworming programs, grazing management, biological control, supplementary feeding and breeding approaches are discussed.     

Modeling Water Quality Impacts of Cellulosic Biofuel Production from Corn Silage

The growing interest in the use of alternative biomass products for fuel production requires a thorough understanding of the environmental impacts associated with the production of these bioenergy crops. Corn silage is a potential bioenergy feedstock; however, water quality implications for its utilization as a biofeedstock are not understood. The objective of this work was to evaluate water quality impacts associated with corn silage production. The GLEAMS-NAPRA model was used to quantify runoff, percolation, erosion, nitrate-nitrogen, total phosphorus, and pesticide losses attributed to the production of corn silage with and without winter cover crops for two tillage options (conventional tillage and no till) on three Indiana soils. Results revealed that corn silage would generate greater annual surface runoff (1 to 6 mm) and percolation (1 to 20 mm) compared with corn grain and grain plus stover cropping systems. Silage/winter cereal rye cover crop reduced annual surface runoff and percolation and was strongly influenced by increases in evapotranspiration, when compared with continuous silage production. Silage managed with winter cereal rye cover crop influenced water quality by reducing annual nitrate losses with runoff from a low of 14 % to a high of 27 %, with relatively no effect because of tillage management. No-till practice on silage system produced significantly greater phosphorus losses (7.46 to 18.07 kg/ha) in comparison to silage/cereal rye, corn grain, and grain plus stover harvest (p?<?0.05). For every 1,000 l of ethanol produced from corn silage, erosion losses ranged from 0.07 to 0.95 t/ha for conventional tillage practices and from 0.06 to 0.83 t/ha for no-till practices. The feasibility of cropping systems such as corn silage/cereal rye could contribute to large-scale biomass production but should be further investigated.     

Spatial and temporal distribution of endemic entomopathogenic nematodes in a heterogeneous vegetable production landscape

Entomopathogenic nematodes within the families Steinernematidae and Heterorhabditidae (Order: Rhabditida) are potential biological control agents for many soil-dwelling vegetable pests. However, their low persistence and efficacy after field releases have resulted in limited use in pest management programs. Understanding the factors regulating natural populations of entomopathogenic nematodes may provide insight into practices to conserve populations within production systems. A series of investigations were conducted within a vegetable production area in Willard, Ohio during 2000–2003 to gain insight into the population ecology of endemic populations of entomopathogenic nematodes. A total of 440 sites across four habitats associated with the production landscape were sampled to ascertain the natural occurrence of these beneficial nematodes. Habitats included cultivated areas, grassy banks adjacent to cultivated areas, undisturbed shrub lands and forests. Twelve sites along grassy banks were monitored over a growing season to estimate associations between abiotic and biotic factors and endemic populations. Entomopathogenic nematodes were only detected along grassy banks adjacent to the cultivated areas; nematodes were recovered from 15 to 30% of sites sampled in 2001 and 2002, respectively. Two species of nematodes were isolated, Heterorhabditis bacteriophora Poinar and Steinernema feltiae Filipjev. H. bacteriophora was the most prevalent nematode species and was recovered from 60% of positive samples. Nematode populations varied temporally and spatially along grassy banks; mean population density over the growing period was 1313 infective juveniles/m². Neither macro- nor microarthropod communities nor soil temperature differed between sites at which nematodes were detected and those at which nematodes were not detected. Soil moisture, however, was associated with the occurrence and persistence of nematodes along grassy banks; mean soil moisture at sites at which nematodes were detected and those sites at which nematodes were not detected was 37.3 and 26.8%, respectively. Water management is an important component of vegetable production and our results suggest that soil moisture manipulation would be important in the establishment and sustained presence of entomopathogenic nematode populations within cultivated areas over the growing season.     

Conserving and Enhancing Biological Control of Nematodes

Conservation biological control is the modification of the environment or existing practices to protect and enhance antagonistic organisms to reduce damage from pests. This approach to biological control has received insufficient attention compared with inundative applications of microbial antagonists to control nematodes. This review provides examples of how production practices can enhance or diminish biological control of plant-parasitic nematodes and other soilborne pests. Antagonists of nematodes can be enhanced by providing supplementary food sources such as occurs when organic amendments are applied to soil. However, some organic amendments (e.g., manures and plants containing allelopathic compounds) can also be detrimental to nematode antagonists. Plant species and genotype can strongly influence the outcome of biological control. For instance, the susceptibility of the plant to the nematode can determine the effectiveness of control; good hosts will require greater levels of suppression than poor hosts. Plant genotype can also influence the degree of rhizosphere colonization and antibiotic production by antagonists, as well the expression of induced resistance by plants. Production practices such as crop rotation, fallow periods, tillage, and pesticide applications can directly disrupt populations of antagonistic organisms. These practices can also indirectly affect antagonists by reducing their primary nematode host. One of the challenges of conservation biological control is that practices intended to protect or enhance suppression of nematodes may not be effective in all field sites because they are dependent on indigenous antagonists. Ultimately, indicators will need to be identified, such as the presence of particular antagonists, which can guide decisions on where it is practical to use conservation biological control. Antagonists can also be applied to field sites in conjunction with conservation practices to improve the consistency, efficacy, and duration of biological control. In future research, greater use should be made of bioassays that measure nematode suppression because changes in abundance of particular antagonists may not affect biological control of plant parasites.     

Reflections on Plant and Soil Nematode Ecology: Past,Present and Future

The purpose of this review is to highlight key developments in nematode ecology from its beginnings to where it stands today as a discipline within nematology. Emerging areas of research appear to be driven by crop production constraints, environmental health concerns, and advances in technology. In contrast to past ecological studies which mainly focused on management of plant-parasitic nematodes, current studies reflect differential sensitivity of nematode faunae. These differences, identified in both aquatic and terrestrial environments include response to stressors, environmental conditions, and management practices. Methodological advances will continue to influence the role nematodes have in addressing the nature of interactions between organisms, and of organisms with their environments. In particular, the C. elegans genetic model, nematode faunal analysis and nematode metagenetic analysis can be used by ecologists generally and not restricted to nematologists.     

Microbial control of plant-parasitic nematodes: a five-party interaction

Plant-parasitic nematodes cause significant economic losses to a wide variety of crops. Chemical control is a widely used option for plant-parasitic nematode management. However, chemical nematicides are now being reappraised in respect of environmental hazard, high costs, limited availability in many developing countries or their diminished effectiveness following repeated applications. This review presents progress made in the field of microbial antagonists of plant-parasitic nematodes, including nematophagous fungi, endophytic fungi, actinomycetes and bacteria. A wide variety of microorganisms are capable of repelling, inhibiting or killing plant-parasitic nematodes, but the commercialisation of these microorganisms lags far behind their resource investigation. One limiting factor is their inconsistent performance in the field. No matter how well suited a nematode antagonist is to a target nematode in a laboratory test, rational management decision can be made only by analysing the interactions naturally occurring among “host plant–nematode target–soil–microbial control agent (MCA)–environment”. As we begin to develop a better understanding of the complex interactions, microbial control of nematodes will be more fine-tuned. Multidisciplinary collaboration and integration of biological control with other control methods will␣also contribute to more successful control practices.     

Control of foliar phytoparasitic nematodes through sustainable natural materials: Current progress and challenges

Nematodes are hidden enemies that inhibit the entire ecosystem causing adverse effects on animals and plants, leading to economic losses. Management of foliar phytoparasitic nematodes is an excruciating task. Various approaches were used to control nematodes dispersal, i.e., traditional practices, resistant cultivars, plant extract, compost, biofumigants, induced resistance, nano-biotechnology applications, and chemical control. This study reviews the various strategies adopted in combating plant-parasitic nematodes while examining the benefits and challenges. The significant awareness of biological and environmental factors determines the effectiveness of nematode control, where the incorporation of alternative methods to reduce the nematodes population in plants with increasing crop yield. The researchers were interested in explaining the fundamental molecular mechanisms, providing an opportunity to deepen our understanding of the sustainable management of nematodes in croplands. Eco-friendly pesticides are effective as a sustainable nematodes management tool and safe for humans. The current review presents the eco-friendly methods in controlling nematodes to minimize yield losses, and benefit the agricultural production efficiency and the environment.     

How do host immune responses affect nematode infections?

Host immune responses limit, and in some instances eliminate, nematode infections. There is considerable interest in enhancing these natural processes by the use of antinematode vaccines to achieve control of infection or disease. How nematodes are damaged is unclear. Worms might be damaged directly by effector cells and molecules of the immune system. Alternatively, they might be damaged by the physiological stress of their efforts to resist attack. Separating these possibilities could have important implications for approaches to the control of nematode infections and the disease that they cause.     

Effect of Soils from Six Management Systems on Root-knot Nematodes and Plant Growth in Greenhouse Assays

The effects of soil management systems on root-knot nematode (Meloidogyne incognita) eggs and gall incidence on tomato (Lycopersicon esculentum) and cucumber (Cucumis sativus) following tomato were evaluated. Soil was collected from a replicated field experiment in which six management systems were being assessed for vegetable production. Soil management systems were conventional production, organic production, bahiagrass (Paspalum notatum) pasture, bahiagrass: Stylosanthes (Stylosanthes guianensis) pasture, bare ground fallow, and weed fallow. Soil was collected from field plots and used in greenhouse experiments. Identification of egg-parasitic fungi and the incidence of root-knot nematode galling were assessed both on tomato and cucumber planted in the same pots following the removal of tomato plants. Organic, bare ground fallow and conventional production treatments reduced galling both on tomato and on cucumber following tomato. Although no treatment consistently enhanced egg-parasitic fungi, management system did affect egg viability and the types of fungi isolated from parasitized eggs.     

Early Crop Root Destruction for Management of Tobacco Cyst Nematodes

Prompt tillage after crop harvest was investigated as a cultural control for the tobacco cyst nematode, Globodera tabacum tabacum, on stalk-cut broadleaf cigar wrapper tobacco. Stalk stumps and roots remaining after harvest were destroyed by tilling immediately or from 2 to 6 wk after harvest in field experiments over 4 yr. Cyst nematode Pf/Pi ratios ranged from 0.65 to 1.62 when plants were tilled immediately after harvest and 1.13 to 5.88 when tillage was delayed. Nematode population development was monitored by inoculating plants in pots placed in fields with J2 in eggs and sampling over time (8 to 18 wk). Three generations per year were observed, and G. t. tabacum generation time was as short as 6 wk for each generation. Destroying stalks and root systems remaining after harvesting stalk-cut broadleaf cigar wrapper tobacco removes the host to preclude development of nematodes at the end of the second and entire third generation. Early tillage resulted in consistently lower tobacco cyst nematode populations than allowing viable roots to remain in fields for an additional 8 to 18 wk. This management tactic reduces the need for nematicide application to slow nematode population increases over time and can reduce losses due to infection by G. t. tabacum.     

Biocontrol of root-knot nematode infected banana plants by some marine algae

Root-knot nematodes are serious pests that cause losses of a wide range of different crops. Nematodes are controlled mainly by nematicides which cause pollution and have serious effects on all living organisms including human beings. Therefore, discovering alternative methods to control plant parasitic nematodes was attempted during the last few years to avoid pesticides hazards. Four species of marine algae (Ulva lactuca, Jania rubens, Laurencia obtusa and Sargassum vulgare) were tested to control root-knot nematode, (Meloidogyne spp.) infecting banana plants (Musa spp.). All the treatments significantly (p ≤ 0.05) reduced the rate of build-up compared with the check. U. lactuca alga gave the best results in reducing the number of galls (73.68%) and the final population of nematode (56.78%). The chemical analysis of all tested materials revealed that U. lactuca had the highest amount of phenolics (10.39 mg GAE/g dry wt). This may explain the remarkable high capability of U. lactuca to control root-knot nematode infections. Also, the same alga was the best treatment and showed maximum growth when compared with other algae and the check. For instance, shoot weight of U. lactuca surpassed the other treatments, even that of non-nematizied check one, giving high increase percentage.     

Invertebrate pests and diseases of sweetpotato (Ipomoea batatas): a review and identification of research priorities for smallholder production

Sweetpotato has been the subject of little research worldwide compared with other major crop staples, and this is especially so for less developed countries where sweetpotato is critical for food security. This review synthesises information on plant protection issues that affect smallholder sweetpotato farmers in less developed countries to identify major issues and suggest research priorities. Though the pests and diseases of sweetpotato in less developed countries are largely common to industrialised systems, their relative importance differs and losses tend to be more severe as a result of differing agronomic practices and relative unavailability of management options and technical support that are important in developed countries. Smallholders are heavily reliant on cultural practices such as traditional forms of biological control using ants and livestock, fallowing and composting (sometimes with plant materials having biocidal properties). Crop protection methods that have been developed for use in sweetpotato production in developed countries, such as pathogen‐tested planting material, early maturing varieties, pheromone trapping and pesticides are less accessible to, and relevant for, smallholders. Smallholders also typically harvest a given crop progressively which extends the period over which storage roots are potentially vulnerable to attack but reduces the risk of post‐harvest losses. Human population growth in developing countries is leading to an increase in cropping intensity with shorter fallow periods and more years of continuous crops. This has the dual effect of depleting soil nutrients and increasing the potential for pest and pathogen build‐up. Associated with this, the adoption of strategies to manage crop nutrition, such as not burning crop residues, promote carryover of pests and pathogen inocula. As a consequence of these factors, sweetpotato yield losses from diseases, especially viruses, and pests, particularly weevils, can be high. Climate change is likely to result in more frequent drought and this will increase losses caused by sweetpotato weevils that are favoured by dry conditions. This review of sweetpotato pests and their management options concludes with suggestions for some future research priorities including the combination of traditional practices that have pest management outcomes with relevant practices from industrial production that are able to be transferred or modified for use in smallholder production. Increased technical support for decision making and diagnostics, including molecular approaches that have scope for field use, will be important in reducing the burden imposed by biotic threats to this important global crop.     

Understanding the role of wild ruminants in anthelmintic resistance in livestock

Wild ruminants are susceptible to infection from generalist helminth species, which can also infect domestic ruminants. A better understanding is required of the conditions under which wild ruminants can act as a source of helminths (including anthelmintic-resistant genotypes) for domestic ruminants, and vice versa, with the added possibility that wildlife could act as refugia for drug-susceptible genotypes and hence buffer the spread and development of resistance. Helminth infections cause significant productivity losses in domestic ruminants and a growing resistance to all classes of anthelmintic drug escalates concerns around helminth infection in the livestock industry. Previous research demonstrates that drug-resistant strains of the pathogenic nematode Haemonchus contortus can be transmitted between wild and domestic ruminants, and that gastro-intestinal nematode infections are more intense in wild ruminants within areas of high livestock density. In this article, the factors likely to influence the role of wild ruminants in helminth infections and anthelmintic resistance in livestock are considered, including host population movement across heterogeneous landscapes, and the effects of climate and environment on parasite dynamics. Methods of predicting and validating suspected drivers of helminth transmission in this context are considered based on advances in predictive modelling and molecular tools.     

Rice root-knot nematode (Meloidogyne graminicola) infestation in rice

Rice (Oryza sativa) is an important staple food crop for majority of human population in the world in general and in Asia in particular. However, among various pests and diseases which constitute important constraints in the successful crop production, plant parasitic nematodes play an important role and account for yield losses to the extent of 90%. The major nematode pests associated with rice are Ditylenchus angustus, Aphelenchoides besseyi, Hirschmanniella spp., Heterodera oryzicola and Meloidogyne graminicola. However, rice root-knot nematode (M. graminicola) happens to be the most important pest and is prevalent in major rice producing countries of the world. In India, the distribution of M. graminicola in rice growing areas of different states has been documented in nematode distribution atlas prepared by All India Coordinated Research Project (Nematodes) and published by Directorate of Information and Publications of Agriculture, Indian Council of Agricultural Research, New Delhi, India during 2010. M. graminicola affected rice plants show stunting and chlorosis due to the characteristic terminal swellings/galls on the roots which ultimately result in severe reduction in growth and yield. Number of eco-friendly management technologies against M. graminicola have been developed and demonstrated, including the use of bioagents for minimising the losses due to rice root-knot nematode. This review is focused on collating information to understand the current scenario of rice root-knot nematodes with greater emphasis on its ecological requirements, damage symptoms, biology, morphology, host range and management strategies.     

The cholinomimetic morantel as an open channel blocker of the <Emphasis Type="Italic">Ascaris suum</Emphasis> ACR-16 nAChR

Nematode parasite infections pose a significant threat in human and veterinary medicine. At least a third of the world’s population is at risk from nematode parasite infections. These infections not only cause health problems, but also cause loss of livestock production and hence, economic losses. Anthelmintic drugs are the mainstay by which control of nematode parasite infections is achieved. Many of the currently available anthelmintics act on nicotinic acetylcholine receptors (nAChRs). However, the detailed mode of action (MOA) of these anthelmintics is not clearly understood. Elucidation of the MOA of anthelmintics is highly desirable; an in-depth knowledge of the MOA will better inform on mechanisms of resistance development and on ways to slow down or overcome resistance. The cholinomimetic anthelmintic, morantel, has a complex MOA involving the activation and block of levamisole-sensitive single nAChR channels (L-type nAChR or L-nAChR). More recently, morantel has been demonstrated to activate Haemonchus contortus and Parascaris equorum ACR-26/ACR-27 nAChRs expressed in Xenopus laevis oocytes. Previous studies in our laboratory, however, have shown morantel does not activate the nicotine-sensitive nAChR (N-type nAChR or N-nAChR), Ascaris suum ACR-16 (Asu-ACR-16). In this study, we used two-electrode voltage-clamp (TEVC) electrophysiology to investigate the inhibitory effects of morantel, on expressed Asu-ACR-16 nAChRs in X. laevis oocytes. Our results show that morantel acts as a non-competitive antagonist on Asu-ACR-16. This non-competitive antagonism by morantel was further demonstrated to be voltage-sensitive. We conclude based on our findings that morantel is a non-competitive voltage-sensitive open channel blocker of Asu-ACR-16.     

Pathogens,Pests, and Economics: Drivers of Honey Bee Colony Declines and Losses

The Western honey bee (Apis mellifera) is responsible for ecosystem services (pollination) worth US$215 billion annually worldwide and the number of managed colonies has increased 45% since 1961. However, in Europe and the U.S., two distinct phenomena; long-term declines in colony numbers and increasing annual colony losses, have led to significant interest in their causes and environmental implications. The most important drivers of a long-term decline in colony numbers appear to be socioeconomic and political pressure on honey production. In contrast, annual colony losses seem to be driven mainly by the spread of introduced pathogens and pests, and management problems due to a long-term intensification of production and the transition from large numbers of small apiaries to fewer, larger operations. We conclude that, while other causal hypotheses have received substantial interest, the role of pests, pathogens, and management issues requires increased attention.     

The Future of Nematode Management in Cotton

The importance of plant-parasitic nematodes as yield-limiting pathogens of cotton has received increased recognition and attention in the United States in the recent past. This paper summarizes the remarks made during a symposium of the same title that was held in July 2007 at the joint meeting of the Society of Nematologists and the American Phytopathological Society in San Diego, California. Although several cultural practices, including crop rotation, can be effective in suppressing the populations of the important nematode pathogens of cotton, the economic realities of cotton production limit their use. The use of nematicides is also limited by issues of efficacy and economics. There is a need for development of chemistries that will address these limitations. Also needed are systems that would enable precise nematicide application in terms of rate and placement only in areas where nematode population densities warrant application. Substantial progress is being made in the identification, characterization and mapping of loci for resistance to Meloidogyne incognita and Rotylenchulus reniformis. These data will lead to efficient marker-assisted selection systems that will likely result in development and release of nematode-resistant cotton cultivars with superior yield potential and high fiber quality.Cotton (Gossypium hirsutum) is the most important fiber crop in the world, and current lint production in the US accounts for nearly one quarter of world supply. The land devoted to cotton production in the US peaked in 1926 at approximately 18 million hectares. The advent of mechanized farming and the availability of effective, relatively low-cost fertilizers, pesticides and improved cotton cultivars after World War II allowed the production of significantly greater yields per unit area and total hectares planted declined. United States production of cotton lint in the past 5 years has varied from 3.0 x 10⁹ kg to 4.4 x 10⁹ kg from approximately 5 million hectares. Additionally, cotton seed is a valuable source of vegetable oil, ruminant animal feed and other feed products.Since World War II, cotton cultivation has been increasingly dependent on inputs of pesticides for weed and insect control. Historically, the cotton boll weevil, Anthonomus grandis, was the most costly pest of cotton in the US. Until recently, the combination of crop loss due to this insect directly and the expense of insecticides for control amounted to several billion dollars annually. The success of the Boll Weevil Eradication Program coordinated by the US Department of Agriculture has resulted in a major reduction in insecticide usage and improved profitability for growers and has led to a resurgence of cotton production in the southeastern US. In addition, the widespread use of transgenic cotton cultivars (currently 92.7% of the crop) with resistance to herbicides and/or lepidopteran insects has further reduced total pesticide usage on the crop (USDA-Agricultural Marketing Service, 2007). Reductions in losses from weeds and insects as a result of the deployment of transgenic traits and the boll weevil eradication program have allowed the cotton industry to focus on other pest problems, especially nematodes.Modern cotton production in the US is intensive, highly mechanized and dependent on a local infrastructure to support this industry. Equipment for cotton harvesting and lint processing, including cotton pickers, modules for storing seed cotton, and gins, are highly specialized and generally not used for other crops. The necessity of an exclusive infrastructure to support cotton production has two important implications: (i) cotton is frequently grown in monoculture, and (ii) cotton typically has a greater impact on local economies than grain crops because of the jobs created to serve the industry.The damage potential of plant-parasitic nematodes to cotton has been recognized since the late 19th century. Classic work by Atkinson demonstrated the pathogenicity of Meloidogyne incognita to cotton and the role of this nematode in Fusarium wilt of cotton (Atkinson, 1892, 1899). Plant-parasitic nematodes, however, received only limited study as cotton pathogens until the 1950s. Currently, the four most damaging species of plant-parasitic nematodes affecting cotton in the US are the southern root-knot (Meloidogyne incognita), reniform (Rotylenchulus reniformis), Columbia lance (Hoplolaimus columbus) and sting (Belonolaimus longicaudatus) (Blasingame, 1993; Koenning et al., 1999; Starr et al., 2005; Blasingame, 2006). Estimated losses of cotton lint yield by these pathogens in the US have increased from 1% to 2% in the 1950s to more than 4% in 2000 (Blasingame, 2006). This increase in estimated losses due to plant-parasitic nematodes can be attributed to several factors: (i) the lack of resistant cultivars, (ii) limited use of crop rotation in many areas, (iii) increased awareness of pathogenic nematodes as production constraints, especially the reniform nematode, (iv) the loss of highly effective, low-cost, fumigant nematicides, and (v) a recent increase in cotton production in the southeastern US.     

Sentinel soil invertebrate taxa as bioindicators for forest management practices

The objectives of the present study were to explore the potential of soil invertebrate taxa (families or genera) to evaluate forest management practices. An experiment with four treatments: control, understory removal, Cassia alata (a legume shrub) addition, and both understory removal and C. alata addition, was conducted at Heshan Hilly Land Interdisciplinary Experimental Station, Guangdong, China. Redundancy analysis showed that some bacterivores and fungivores of soil invertebrates (nematodes, mites, collembolans) were correlated positively, but some predators and omnivores were correlated negatively with forest management practices. C. alata addition increased the abundance of the high trophic-level nematodes and mites, which indicated C. alata addition was a good forest management practice in terms of improved soil food web structure. In contrast, removal of forest understory plants appeared to disturb the ecosystem by suppressing high-trophic groups of soil invertebrates, demonstrating that understory removal was not a good forest management practice. Redundancy analysis also showed that soil fauna at the genus or family level can be used as biological indicators for forest management practices. Specifically, some high trophic-level nematode genera such as Eudorylaimus, Chrysonema, Iotonchus and Thornia were suppressed significantly by understory removal and some nematode genera such as Prismatolaimus, Eudorylaimus, Chrysonema, and Thornia and one common mite genus Rhodacarus in high trophic-level were enriched significantly by legume addition.