Examination of the effect of aphid vector population composition on the spatial dynamics of citrus tristeza virus spread by stochastic modeling

Aphid vector species population composition is known to affect the spatial patterns of citrus tristeza virus (CTV) and the changes in these patterns o ver time. However, the biological processes that are associated with virus spread have not been well defined. The spatiotemporal dynamics of CTV were examined using data collected from research plots in the Dominican Republic and Costa Rica, where the brown citrus aphid (BCA), Toxoptera citricida, w as the predominant species, and in Florida, where the BCA was absent and th e melon aphid, Aphis gossypii, was the predominant vector. Data were analyz ed using a spatiotemporal stochastic model for disease spread, and paramete r values were evaluated using Markov chain Monte Carlo stochastic integrati on methods. Where the melon aphid was the dominant species, the model param eter likelihood values supported the hypothesis that the disease was spread through a combination of random background transmission (transmission orig inating from inoculum sources outside the plot) and a local interaction (tr ansmission from inoculum sources within the plot) operating over short dist ances. Conversely, when BCA was present, results often suggested a local sh ort-range transmission interaction that was not restricted to nearest-neigh bor interactions and that the presence of background infection was not nece ssary to explain the observations.