Models for integrated pest control and their biological implications

Successful integrated pest management (IPM) control programmes depend on many factors which include host-parasitoid ratios, starting densities, timings of parasitoid releases, dosages and timings of insecticide applications and levels of host-feeding and parasitism. Mathematical models can help us to clarify and predict the effects of such factors on the stability of host-parasitoid systems, which we illustrate here by extending the classical continuous and discrete host-parasitoid models to include an IPM control programme. The results indicate that one of three control methods can maintain the host level below the economic threshold (ET) in relation to different ET levels, initial densities of host and parasitoid populations and host-parasitoid ratios. The effects of host intrinsic growth rate and parasitoid searching efficiency on host mean outbreak period can be calculated numerically from the models presented. The instantaneous pest killing rate of an insecticide application is also estimated from the models. The results imply that the modelling methods described can help in the design of appropriate control strategies and assist management decision-making. The results also indicate that a high initial density of parasitoids (such as in inundative releases) and high parasitoid inter-generational survival rates will lead to more frequent host outbreaks and, therefore, greater economic damage. The biological implications of this counter intuitive result are discussed.     

Distinct soil microbial diversity under long-term organic and conventional farming

Low-input agricultural systems aim at reducing the use of synthetic fertilizers and pesticides in order to improve sustainable production and ecosystem health. Despite the integral role of the soil microbiome in agricultural production, we still have a limited understanding of the complex response of microbial diversity to organic and conventional farming. Here we report on the structural response of the soil microbiome to more than two decades of different agricultural management in a long-term field experiment using a high-throughput pyrosequencing approach of bacterial and fungal ribosomal markers. Organic farming increased richness, decreased evenness, reduced dispersion and shifted the structure of the soil microbiota when compared with conventionally managed soils under exclusively mineral fertilization. This effect was largely attributed to the use and quality of organic fertilizers, as differences became smaller when conventionally managed soils under an integrated fertilization scheme were examined. The impact of the plant protection regime, characterized by moderate and targeted application of pesticides, was of subordinate importance. Systems not receiving manure harboured a dispersed and functionally versatile community characterized by presumably oligotrophic organisms adapted to nutrient-limited environments. Systems receiving organic fertilizer were characterized by specific microbial guilds known to be involved in degradation of complex organic compounds such as manure and compost. The throughput and resolution of the sequencing approach permitted to detect specific structural shifts at the level of individual microbial taxa that harbours a novel potential for managing the soil environment by means of promoting beneficial and suppressing detrimental organisms.     

Genetic and metabolic diversity of streptomycetes in pulp and paper mill effluent treated crop fields

Irrigation of farm field with water mixed with pulp and paper mill effluent from Century pulp and paper mill in Uttrakhand state of India for over last 25 years in succession increased streptomycetes population (120 × 10⁵) compared to the fresh water irrigated fields (48 × 10³ in WIF). Denaturing gradient gel electrophoresis, amplified ribosomal DNA restriction analysis, 16S rRNA gene sequencing, BIOLOG™ substrate usage, production of extracellular enzymes (xylanase and cellulase) and plant growth promoting attributes were applied to monitor changes in genetic and metabolic diversity of streptomycetes. Significant variation was observed for production of extracellular enzymes, Indolic compounds, siderophore and P-solubilisation among isolates. Metabolic substrate usage of Streptomyces isolates was evaluated using the BIOLOG™ GP2 plates and unique carbon substrate usage profiles were observed. Based on 16S rRNA gene sequencing, the isolates were identified as Streptomyces variabilis, Streptomyces spp. S. glaucescens, S. viridochromogenes, S. cinnabarinus, S. aburaviensis, S. viridis, S. xylophagus, S. macrosporeus, S. thermocarboxydus, and S. albogriseolus. The diversity index parameters like Shannon index, reciprocal of Simpson’s index (1/D), and Pielou index of evenness based on ARDRA revealed that streptomycetes community in effluent irrigated field (EIF) was more diverse. DGGE profiles of Streptomyces specific 16S rRNA gene fragments (16S-DGGE) amplified directly from soil samples were highly similar in both soils.     

Cascade effects of crop species richness on the diversity of pest insects and their natural enemies

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology.We explore the effects of crop species richness on the diversity of pest insects and their natural enemies.Using data from a four-year experiment with five levels of crop species richness,we found that crop species richness significantly affected the pest species richness,but there were no significant effects on richness of the pests’natural enemies.In contrast,the species richness of pest insects significantly affected their natural enemies.These findings suggest a cascade effect where trophic interactions are strong between adjacent trophic levels,while the interactions between connected but nonadjacent trophic levels are weakened by the intermediate trophic level.High crop species richness resulted in a more stable arthropod community compared with communities in monoculture crops.Our results highlight the complicated cross-trophic interactions and the crucial role of crop diversity in the food webs of agro-ecosystems.     

Functional and structural microbial diversity in organic and conventional viticulture: organic farming benefits natural biocontrol agents

Statistically significant differences in the structure and function of above-ground grapevine-associated microorganisms from organically and conventionally managed vineyards were found. Aureobasidium pullulans, a copper-detoxifying fungus and biocontrol agent, plays a key role in explaining these differences. The black fungus was strongly enriched in the communities of organically managed plants and yielded a higher indigenous antiphytopathogenic potential.     

Developing a risk indicator to comparatively assess environmental risks posed by microbial and conventional pest control agents

Selected biological control agents and conventional pesticides were used to critically review the applicability of a newly developed Risk Indicator (RI) system. Five basic components are proposed for the calculation of the overall environmental risk score: persistence of the active ingredient, dispersal potential, range of non-target organisms that are affected, and direct and indirect effects on the ecosystem. Several risk measurement systems were reviewed; risk categories in the proposed system were modified from a model developed for classical biocontrol agents. Additionally, one new category was included, to assess the risks to vertebrate non-target species. Besides a detailed discussion of the new RI model, the suitability of the model was demonstrated by calculating the risk scores for 17 selected products. It became obvious that the environmental risk score varied greatly within the assessed chemical products, and also within the group of biological products. The use pattern greatly influenced the estimated environmental risk posed by any given product. The overall environmental risk score varied between a very low risk score of 24 (Coniothyrium minitans, soil application) and a near maximum risk score of 4275 (high risk reference DDT, foliar spray). The proposed model can be used to communicate environmental risk and to design lower risk integrated pest management strategies. It is suggested that the proposed RI system may serve to define low risk and reduced risk pesticides. Yet, it remains debatable whether the RI will be useful in determining acceptability of data waivers for regulatory purposes.     

Protein monoubiquitination and polyubiquitination generate structural diversity to control distinct biological processes

Ubiquitination involves the attachment of ubiquitin (Ub) to lysine residues on substrate proteins or itself, which can result in protein monoubiquitination or polyubiquitination. Polyubiquitination through different lysines (seven) or the N-terminus of Ub can generate different protein-Ub structures. These include monoubiquitinated proteins, polyubiqutinated proteins with homotypic chains through a particular lysine on Ub or mixed polyubiquitin chains generated by polymerization through different Ub lysines. The ability of the ubiquitination pathway to generate different protein-Ub structures provides versatility of this pathway to target proteins to different fates. Protein ubiquitination is catalyzed by Ub-conjugating and Ub-ligase enzymes, with different combinations of these enzymes specifying the type of Ub modification on protein substrates. How Ub-conjugating and Ub-ligase enzymes generate this structural diversity is not clearly understood. In the current review, we discuss mechanisms utilized by the Ub-conjugating and Ub-ligase enzymes to generate structural diversity during protein ubiquitination, with a focus on recent mechanistic insights into protein monoubiquitination and polyubiquitination.     

Parasitoid diversity reduces the variability in pest control services across time on farms

Recent declines in biodiversity have increased interest in the link between biodiversity and the provision and sustainability of ecosystem services across space and time. We mapped the complex network of interactions between herbivores and parasitoids to examine the relationship between parasitoid species richness, functional group diversity and the provision of natural pest control services. Quantitative food webs were constructed for 10 organic and 10 conventional farms. Parasitoid species richness varied from 26 to 58 species and we found a significant positive relationship between parasitoid species richness and temporal stability in parasitism rates. Higher species richness was associated with lower variation in parasitism rate. A functional group analysis showed significantly greater parasitoid species complementarity on organic farms, with on average more species in each functional group. We simulated parasitoid removal to predict whether organic farms experienced greater robustness of parasitism in the face of local extinctions. This analysis showed no consistent differences between the organic and conventional farm pairs in terms of loss of pest control service. Finally, it was found that the different habitats that make up each farm do not contribute equally to parasitoid species diversity, and that hedgerows produced more parasitoid species, significantly more so on organic farms.     

Recent advances in biological control of pest insects by using viruses in China

Insect viruses are attractive as biological control agents and could be a feasible alternative to chemical insecticides in the management of insect infestations. This review describes recent advances in the development of wild-type and genetically modified viruses as insecticides. A new strategy of application of insect viruses in China is reviewed. Also, the assessment of biosafety of genetically modified Helicoverpa armigera Nucleopolyhedovirus (HearNPV) is emphasized as a case-study. Foundation itims: The 863 projects (2006AA10A210) from MOST.     

The value of woody hedgerows for moth diversity on organic and conventional farms

Habitat destruction and degradation are important drivers of biodiversity loss within agro-ecosystems. However, little is known about the effect of farming practices and the value of woody hedgerows on Lepidoptera in North America. The purpose of this work was to study moth diversity in woody hedgerows and croplands of organic and conventional farms. In addition, the influence of vegetation composition and abiotic variables on species richness, abundance, and composition was examined. Moths were sampled with light traps during six weeks in the summer of 2001. Vegetation data and abiotic variables were obtained for all sites. In total, 26,020 individuals from 12 families and 408 species were captured. Most species were uncommon. Only 35 species included >100 individuals while for 71% of species <10 individuals were found. The Noctuidae represented 221 species and 85% of all individuals captured. Woody hedgerows harbored more species and in greater number than croplands. There was no significant difference in moth diversity between organic and conventional farms, except that the Notodontidae were significantly more species rich in organic than in conventional sites. Results show that species richness, abundance, and composition were greatly influenced by habitat types (hedgerow versus crop field) and abiotic variables (minimum temperature which was correlated to moon illumination, rainfall, and cloud cover). Moth species composition was significantly correlated to vegetation composition. This study broadens our understanding of the factors driving moth diversity and expands our knowledge of their geographic range. The maintenance of noncrop habitats such as woody hedgerows within agro-ecosystems seems paramount to preserving the biodiversity and abundance of many organisms, including moths.     

Neighbouring crop diversity mediates the effect of Bt cotton on insect community and leaf damage in fields

Effects of large-scale cultivation of transgenic crops on agricultural biodiversity remain unclear, particularly in the context of complex ecological interactions between transgenic crops and other organisms. Here we conducted a comprehensive survey to investigate the number of species, population abundance, community evenness and dominance of insects and weeds as well as leaf damage to weeds in Bt and non-Bt cotton fields at 27 sites across northern China. The role of neighbouring crop diversity around cotton fields in controlling insects and weeds in the cotton fields was also assessed. In addition, we conducted a 3-year field experiment to verify the results of the survey. Weed diversity in Bt and non-Bt cotton fields was similar, but the species number and diversity indices of insects are significantly decreased in Bt fields aligning with reduced leaf damage to broadleaf plant species including cotton as well as crops in neighbouring plots. The leaf damage to Bt and non-Bt cotton negatively associates with the diversity of neighbouring crops in cotton fields. Our study demonstrates the neighbouring crop diversity mediates the effects of Bt crops on agricultural diversity in complex interactions among transgenic crops, in-field weed and insect communities, and neighbouring crops.

     

Early pest development and loss of biological control are associated with urban warming

Climate warming is predicted to cause many changes in ectotherm communities, one of which is phenological mismatch, wherein one species'' development advances relative to an associated species or community. Phenological mismatches already lead to loss of pollination services, and we predict that they also cause loss of biological control. Here, we provide evidence that a pest develops earlier due to urban warming but that phenology of its parasitoid community does not similarly advance. This mismatch is associated with greater egg production that likely leads to more pests on trees.     

Classical biological control in an ephemeral crop habitat with Anticarsia gemmatalis nucleopolyhedrovirus

Anticarsia gemmatalis nucleopolyhedrovirus(AgNPV) was released as a single spray in soybean at two sites in Louisiana, near Crowley and Baton Rouge, after which viral prevalence and population density were monitored for 3--4 years. Each site had a plot with no treatment (control) and two virus-treated plots, one planted with soybean yearly for 3-4 years, and the other planted with soybean for 3-4 years except for rotation to a different crop in year 2. In year 1, the single spray ofAgNPV resulted in viral prevalence rates ranging from 25--100% A. gemmatalis mortality over the entire growing season. By the end of this season, viral accumulation in soil averaged 4.1 ×10⁴ occlusion bodies (OB)/g at Crowley and 7.4× 10³ OB/g at Baton Rouge, which had a sandier soil than Crowley. At Crowley, prevalence of AgNPVreached 49% insect mortality in the unrotated plot in year 2, and 31% in the rotated plot and 38% in the unrotated plot in year 3, in spite of moderate to low population densities of A. gemmatalis. At Baton Rouge, AgNPV prevalence decreased to peak prevalence rates of 25% insect mortality in year 2,4% in year 3, and 11% in year 4, even though A. gemmatalis population densities were moderate in years 2 and 3. Viral concentration in soil decreased to 2.7 × 10² OB/g (rotated plot) and1.4 × 10⁴ OB/g (unrotated plot) by the end of year 3 at Crowley and to 10 OB/g (rotated plot) and31 OB/g (unrotated plot) by the end of year 4 at Baton Rouge. In forward stepwise multiple regressions, the concentration of OB in soil was significantly (p = 0.0001) and positively correlated with AgNPV prevalence, but correlations of the latter parameter with host population density and rainfall were not significant (p > 0.05). Prevalence rates of the fungal entomopathogen Nomuraea rileyi were significantly (p < 0.01) and negatively correlated with AgNPV prevalence at Crowley but not in the combined data set. Prevalence of N. rileyi was negatively correlated (p = 0.0001) with precipitation and positively correlated (p = 0.0001) with A.gemmatalis population density. The research demonstrated that AgNPV can be introduced and established for long-term suppression of A.gemmatalis in an ephemeral crop habitat, but certain site-related conditions, perhaps relating to soil, are necessary for its continued success. This revised version was published online in July 2006 with corrections to the Cover Date.     

Impact of long-term conventional and organic farming on the diversity of arbuscular mycorrhizal fungi

Previous work has shown considerably enhanced soil fertility in agroecosystems managed by organic farming as compared to conventional farming. Arbuscular mycorrhizal fungi (AMF) play a crucial role in nutrient acquisition and soil fertility. The objective of this study was to investigate the diversity of AMF in the context of a long-term study in which replicated field plots, at a single site in Central Europe, had been cultivated for 22 years according to two organic and two conventional farming systems. In the 23rd year, the field plots, carrying an 18-month-old grass-clover stand, were examined in two ways with respect to AMF diversity. Firstly, AMF spores were isolated and morphologically identified from soil samples. The study revealed that the AMF spore abundance and species diversity was significantly higher in the organic than in the conventional systems. Furthermore, the AMF community differed in the conventional and organic systems: Glomus species were similarly abundant in all systems but spores of Acaulospora and Scutellospora species were more abundant in the organic systems. Secondly, the soils were used to establish AMF-trap cultures using a consortium of Plantago lanceolata, Trifolium pratense and Lolium perenne as host plants. The AMF spore community developing in the trap cultures differed: after 12 months, two species of the Acaulosporaceae (A. paulinae and A. longula) were consistently found to account for a large part of the spore community in the trap cultures from the organic systems but were found rarely in the ones from the conventional systems. The findings show that some AMF species present in natural ecosystems are maintained under organic farming but severely depressed under conventional farming, indicating a potentially severe loss of ecosystem function under conventional farming.