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Location: Subtropical Plant Pathology Research

Title: A method of determining how to balance survey effort for early detection of HLB across host and vector populations.

item MASTIN, ALEXANDER - University Of Salford
item VAN DEN BOSCH, FRANK - Rothamsted Research
item Gottwald, Timothy
item ALONSO CHAVEZ, VASTHI - Rothamsted Research
item PARNELL, STEPHEN - University Of Salford

Submitted to: Journal of Citrus Pathology
Publication Type: Abstract Only
Publication Acceptance Date: 12/20/2016
Publication Date: 5/18/2017
Citation: Mastin, A., Van Den Bosch, F., Gottwald, T.R., Alonso Chavez, V., Parnell, S. 2017. A method of determining how to balance survey effort for early detection of HLB across host and vector populations.. Journal of Citrus Pathology. 4(1):29/45.

Interpretive Summary: Early detection surveillance strategies for HLB rarely consider the division of survey effort between vector and host populations. We use an epidemiological modelling approach to show that the total required sampling effort or cost for early detection of HLB is minimised when either hosts or vectors are sampled, but not both. The choice of whether to sample from hosts or vectors is affected by the epidemiological dynamics of the HLB pathosystem as a whole and the relative sampling costs.

Technical Abstract: Many citrus production areas are currently threatened by HLB. Whilst minimising the risk of spread of the HLB bacterium (Candidatus Liberibacter asiaticus; Las) and insect vector (Diaphorina citri) are important strategies for reducing the risk of HLB entry, there will always be a potential risk of introduction. This means that effective early detection surveillance activities – focussed at detecting Las infection at an early stage – must be in place. Our previous work has demonstrated that the epidemiology of a pathogen (in particular, the rate of epidemic growth) should be considered when developing surveillance strategies [1,2]. The presence of insect vectors as well as host plants in the HLB pathosystem adds another layer of complexity to the issue of surveillance, since it leads to the question of whether to sample from hosts, vectors, or both. Although this question has considerable implications for the design of the surveillance strategy, many surveillance schemes focus on sampling from host plants, with vectors sampled more opportunistically. To investigate this issue further, we have developed a statistical model of host and vector sampling and linked this to a mathematical model of pathogen transmission through the HLB pathosystem as a whole. The resultant model allows us to quantify the relative sampling efforts and/or costs required from hosts and vectors in order to detect a specified incidence of infection in either. From this, we demonstrate that the overall incidence at first detection is minimised when samples are exclusively collected from either hosts or vectors but not from both. As well as identifying whether hosts or vectors should be sampled, our method gives a numerical output which indicates how robust this decision is to changes in sampling costs. This has potential for use as a simple tool to determine where best to place sampling resources whilst accounting for both epidemiological issues and economic constraints.