Range expansion of the sand fly, Lutzomyia shannoni (Dyar) (Diptera: Psychodidae): Climate change, and a heat unit accumulation model

The population dynamics of Lutzomyia shannoni (Dyar), a phlebotomine sand fly, have been monitored in southwestern Kentucky since the discovery of the flies in late 2005. Kentucky represents a significant range expansion for this species which is a competent vector of several diseases of humans and livestock, including Leishmaniasis and vesicular stomatitis virus. Weekly sampling from mid June through late September in 2006 and 2007 using CDC light traps suggested two adult flights per year, in Kentucky. To better understand this species’ phenology in its new habitat, we developed a heat unit accumulation model, and began intensive sampling in April of 2008. We used the model to predict the emergence of this species at three locations; (1) along the southern Kentucky border, (2) in central Kentucky, and (3) in south-central Ohio. The predictions of adult emergence produced by the model have been accurate with respect to field observations of first adult emergence within one day. Sensitivity testing established a forecast horizon of at least two weeks for a forecast with ±2 day accuracy. In addition to major increases in trap catch density over the past four sampling seasons (e.g. ~20 maximum per trap in 2005 to 120 in 2008), we have also observed increasing populations of the mosquito, Culex nigripalpus, which has been historically reported from a range very similar to Lutzomyia shannoni. The significant expansions of these species’ ranges greatly increases the potential disease threats posed by these insects over a broad grographical range.