Imperial College London

Dr John Holt

Faculty of Natural SciencesCentre for Environmental Policy

Visiting Researcher
 
 
 
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j.holt

 
 
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Silwood ParkSilwood Park

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Summary

 

Publications

Publication Type
Year
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35 results found

Holt J, Leach AW, 2019, Linguistic variables as fuzzy sets to model uncertainty in the combined efficacy of multiple phytosanitary measures in pest risk analysis, ECOLOGICAL MODELLING, Vol: 406, Pages: 73-79, ISSN: 0304-3800

Journal article

van der Gaag DJ, Holt J, Leach AW, Loomans AJMet al., 2019, Model of the probability of pest transfer to a site suitable for establishment following their arrival on imported fruit, cut-flower or vegetable produce, CROP PROTECTION, Vol: 117, Pages: 135-146, ISSN: 0261-2194

Journal article

Holt J, Leach AW, Johnson S, Tu DM, Nhu DT, Anh NT, Quinlan MM, Whittle PJL, Mengersen K, Mumford JDet al., 2017, Bayesian Networks to Compare Pest Control Interventions on Commodities Along Agricultural Production Chains., Risk Analysis, Vol: 38, Pages: 297-310, ISSN: 0272-4332

The production of an agricultural commodity involves a sequence of processes: planting/growing, harvesting, sorting/grading, postharvest treatment, packing, and exporting. A Bayesian network has been developed to represent the level of potential infestation of an agricultural commodity by a specified pest along an agricultural production chain. It reflects the dependency of this infestation on the predicted level of pest challenge, the anticipated susceptibility of the commodity to the pest, the level of impact from pest control measures as designed, and any variation from that due to uncertainty in measure efficacy. The objective of this Bayesian network is to facilitate agreement between national governments of the exporters and importers on a set of phytosanitary measures to meet specific phytosanitary measure requirements to achieve target levels of protection against regulated pests. The model can be used to compare the performance of different combinations of measures under different scenarios of pest challenge, making use of available measure performance data. A case study is presented using a model developed for a fruit fly pest on dragon fruit in Vietnam; the model parameters and results are illustrative and do not imply a particular level of fruit fly infestation of these exports; rather, they provide the most likely, alternative, or worst-case scenarios of the impact of measures. As a means to facilitate agreement for trade, the model provides a framework to support communication between exporters and importers about any differences in perceptions of the risk reduction achieved by pest control measures deployed during the commodity production chain.

Journal article

Holt J, Leach A, Mumford JD, MacLeod A, Tomlinson D, Baker R, Christodoulou M, Russo L, Marechal Aet al., 2016, Development of probabilistic models for quantitative pathway analysis of plant pest introduction for the EU territory, Parma, Italy, Publisher: European Food Safety Authority, 2016:EN-1062

This report demonstrates a probabilistic quantitative pathway analysis model that can be used in risk assessment for plant pest introduction into EU territory on a range of edible commodities (apples, oranges, stone fruits and wheat). Two types of model were developed: a general commodity model that simulates distribution of an imported infested/infected commodity to and within the EU from source countries by month; and a consignment model that simulates the movement and distribution of individual consignments from source countries to destinations in the EU. The general pathway model has two modules. Module 1 is a trade pathway model, with a Eurostat database of five years of monthly trade volumes for each specific commodity into the EU28 from all source countries and territories. Infestation levels based on interception records, commercial quality standards or other information determine volume of infested commodity entering and transhipped within the EU. Module 2 allocates commodity volumes to processing, retail use and waste streams and overlays the distribution onto EU NUTS2 regions based on population densities and processing unit locations. Transfer potential to domestic host crops is a function of distribution of imported infested product and area of domestic production in NUTS2 regions, pest dispersal potential, and phenology of susceptibility in domestic crops. The consignment model covers the several routes on supply chains for processing and retail use. The output of the general pathway model is a distribution of estimated volumes of infested produce by NUTS2 region across the EU28, by month or annually; this is then related to the accessible susceptible domestic crop. Risk is expressed as a potential volume of infested fruit in potential contact with an area of susceptible domestic host crop. The output of the consignment model is a volume of infested produce retained at each stage along the specific consignment trade chain.

Report

Leach AW, Levontin P, Holt J, Kell LT, Mumford JDet al., 2014, Identification and prioritization of uncertainties for management of Eastern Atlantic bluefin tuna (Thunnus thynnus), Marine Policy, Vol: 48, Pages: 84-92, ISSN: 0308-597X

In recent decades there has been steady progress towards a risk-based management approach for fisheries. An important first step in a risk analysis framework is scoping to identify, describe and catalog the sources of uncertainty that might have an impact on a fishery. This paper introduces a methodology based on a range of tools to formalize the process of elicitation of uncertainties, from both experts and stakeholders, for the International Commission for the Conservation of Atlantic Tunas (ICCAT). ICCAT is a regional fisheries management organization responsible for the conservation of tunas and other highly migratory fish in the Atlantic Ocean and its adjacent seas. The aim of the elicitation was to identify and prioritize uncertainties for inclusion in Operating Models for Management Strategy Evaluation (MSE). The tool presented in this paper supports the qualitative prioritization of uncertainties, while also visualizing the degree of consensus among stakeholders on particular issues. Perceptions of uncertainty in fisheries often vary widely among scientists, industry and other interest groups, so tools that can facilitate inclusion and representation of different opinions are useful where decision-making depends on broad agreement and more generally, where effective management depends on commitment from stakeholders.

Journal article

Holt J, Leach AW, Schrader G, Petter F, MacLeod A, van der Graag DJ, Baker RHA, Mumford JDet al., 2013, Eliciting and combining decision criteria using a limited palette of utility functions and uncertainty distributions: illustrated by application to Pest Risk Analysis, Risk Analysis, Vol: 34, Pages: 4-16, ISSN: 0272-4332

Utility functions in the form of tables or matrices have often been used to combine discretely-rated decision-making criteria. Matrix elements are usually specified individually, so no one rule or principle can be easily stated for the utility function as a whole. A series of five matrices are presented which aggregate criteria two at a time using simple rules which express a varying degree of constraint of the lower rating over the higher. A further nine possible matrices were obtained by using a different rule either side of the main axis of the matrix to describe situations where the criteria have a differential influence on the outcome. Uncertainties in the criteria are represented by three alternative frequency distributions from which the assessors select the most appropriate. The output of the utility function is a distribution of rating frequencies that is dependent on the distributions of the input criteria. In Pest Risk Analysis (PRA), seven of these utility functions were required to mimic the logic by which assessors for the European and Mediterranean Plant Protection Organisation (EPPO) arrive at an overall rating of pest risk. The framework enables the development of PRAs which are consistent and easy to understand, criticise, compare and change. When tested in workshops, PRA practitioners thought that the approach accorded with both the logic and the level of resolution which they used in the risk assessments

Journal article

Mumford JD, Booy O, RHA B, Rees M, Copp GH, Black K, Holt J, Leach AW, Hartley Met al., 2010, Invasive species risk assessment in Great Britain, Aspects of Applied Biology, Vol: 104, Pages: 49-54, ISSN: 0265-1491

Journal article

Abarshi MM, Mohammed IU, Wasswa P, Hillocks RJ, Holt J, Legg JP, Seal SE, Maruthi MNet al., 2010, Optimization of diagnostic RT-PCR protocols and sampling procedures for the reliable and cost-effective detection of Cassava brown streak virus, JOURNAL OF VIROLOGICAL METHODS, Vol: 163, Pages: 353-359, ISSN: 0166-0934

Journal article

Holt J, Pavis C, Marquier M, Chancellor TCB, Urbino C, Boissot Net al., 2008, Insect-screened cultivation to reduce the invasion of tomato crops by Bemisia tabaci: modelling the impact on virus disease and vector, AGRICULTURAL AND FOREST ENTOMOLOGY, Vol: 10, Pages: 61-67, ISSN: 1461-9555

Journal article

Holt J, 2006, Score averaging for alien species risk assessment: A probabilistic alternative, JOURNAL OF ENVIRONMENTAL MANAGEMENT, Vol: 81, Pages: 58-62, ISSN: 0301-4797

Journal article

Holt J, Davis S, Leirs H, 2006, A model of Leptospirosis infection in an African rodent to determine risk to humans: Seasonal fluctuations and the impact of rodent control, ACTA TROPICA, Vol: 99, Pages: 218-225, ISSN: 0001-706X

Journal article

Holt J, Cooper JE, 2006, A model to compare the suitability of locust hopper targets for control by insecticide barriers, ECOLOGICAL MODELLING, Vol: 195, Pages: 273-280, ISSN: 0304-3800

Journal article

Chancellor TCB, Holt J, Villareal S, Tiongco ER, Venn Jet al., 2006, Spread of plant virus disease to new plantings: A case study of rice tungro disease, ADVANCES IN VIRUS RESEARCH, VOL 66, Vol: 66, Pages: 1-29, ISSN: 0065-3527

Journal article

Holt J, Mushobozi W, Day RK, Knight JD, Kimani M, Njuki J, Musebe Ret al., 2006, A simple Bayesian network to interpret the accuracy of armyworm outbreak forecasts, ANNALS OF APPLIED BIOLOGY, Vol: 148, Pages: 141-146, ISSN: 0003-4746

Journal article

Holt J, Black R, Abdallah R, 2006, A rigorous yet simple quantitative risk assessment method for quarantine pests and non-native organisms, ANNALS OF APPLIED BIOLOGY, Vol: 149, Pages: 167-173, ISSN: 0003-4746

Journal article

Jeger MJ, Holt J, Van den Bosch F, Madden LVet al., 2004, Epidemiology of insect-transmitted plant viruses: modelling disease dynamics and control interventions, PHYSIOLOGICAL ENTOMOLOGY, Vol: 29, Pages: 291-304, ISSN: 0307-6962

Journal article

Zhu L, Black R, Holt J, 2002, International developments in pest risk analysis for phytosanitary decision making: a review of methodologies for pest risk assessment, BCPC International Conference on Pests and Diseases, Publisher: BRITISH CROP PROTECTION COUNCIL, Pages: 911-916

Conference paper

Zhang XS, Holt J, Colvin J, 2001, Synergism between plant viruses: a mathematical analysis of the epidemiological implications, PLANT PATHOLOGY, Vol: 50, Pages: 732-746, ISSN: 0032-0862

Journal article

Zhang XS, Holt J, 2001, Mathematical models of cross protection in the epidemiology of plant-virus diseases, PHYTOPATHOLOGY, Vol: 91, Pages: 924-934, ISSN: 0031-949X

Journal article

Zhang XS, Holt J, Colvin J, 2000, A general model of plant-virus disease infection incorporating vector aggregation, PLANT PATHOLOGY, Vol: 49, Pages: 435-444, ISSN: 0032-0862

Journal article

Grilli MP, Holt J, 2000, Vector feeding period variability in epidemiological models of persistent plant viruses, ECOLOGICAL MODELLING, Vol: 126, Pages: 49-57, ISSN: 0304-3800

Journal article

Zhang XS, Holt J, Colvin J, 2000, Mathematical models of host plant infection by helper-dependent virus complexes: Why are helper viruses always avirulent?, PHYTOPATHOLOGY, Vol: 90, Pages: 85-93, ISSN: 0031-949X

Journal article

Zhu L, Holt J, Black R, 2000, New approaches to pest risk analysis for plant quarantine, International Conference on Pests and Diseases, Publisher: BRITISH CROP PROTECTION COUNCIL, Pages: 495-498, ISSN: 0955-1506

Conference paper

Holt J, Colvin J, Muniyappa V, 1999, Identifying control strategies for tomato leaf curl virus disease using an epidemiological model, JOURNAL OF APPLIED ECOLOGY, Vol: 36, Pages: 625-633, ISSN: 0021-8901

Journal article

Holt J, Chancellor TCB, 1999, Modelling the spatio-temporal deployment of resistant varieties to reduce the incidence of rice tungro disease in a dynamic cropping system, PLANT PATHOLOGY, Vol: 48, Pages: 453-461, ISSN: 0032-0862

Journal article

Smith MC, Holt J, Kenyon L, Foot Cet al., 1998, Quantitative epidemiology of Banana Bunchy Top Virus Disease and its control, PLANT PATHOLOGY, Vol: 47, Pages: 177-187, ISSN: 0032-0862

Journal article

Trumper EV, Holt J, 1998, Modelling pest population resurgence due to recolonization of fields following an insecticide application, JOURNAL OF APPLIED ECOLOGY, Vol: 35, Pages: 273-285, ISSN: 0021-8901

Journal article

Jeger MJ, Van Den Bosch F, Madden LV, Holt Jet al., 1998, A model for analysing plant-virus transmission characteristics and epidemic development, IMA JOURNAL OF MATHEMATICS APPLIED IN MEDICINE AND BIOLOGY, Vol: 15, Pages: 1-18, ISSN: 0265-0746

Journal article

Holt J, Colvin J, 1997, A differential equation model of the interaction between the migration of the Senegalese grasshopper, Oedaleus senegalensis, its predators, and a seasonal habitat, ECOLOGICAL MODELLING, Vol: 101, Pages: 185-193, ISSN: 0304-3800

Journal article

Holt J, Chancellor TCB, 1997, A model of plant virus disease epidemics in asynchronously-planted cropping systems, PLANT PATHOLOGY, Vol: 46, Pages: 490-501, ISSN: 0032-0862

Journal article

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