Abstract
BackgroundBiting midges, Culicoides, of the Obsoletus group and the Pulicaris group have been involved in recent outbreaks of bluetongue virus and the former was also involved in the Schmallenberg virus outbreak in northern Europe.MethodsFor the first time, here we investigate the local abundance pattern of these two species groups in the field by intensive sampling with a grid of light traps on 16 catch nights. Neighboring trap catches can be spatially dependent on each other, hence we developed a conditional autoregressive (CAR) model framework to test a number of spatial and non-spatial covariates expected to affect Culicoides abundance.ResultsThe distance to sheep penned in the corner of the study field significantly increased the abundance level up to 200 meters away from the sheep. Spatial clustering was found to be significant but could not be explained by any known factors, and cluster locations shifted between catch nights. No significant temporal autocorrelation was detected. CAR models for both species groups identified a significant positive impact of humidity and significant negative impacts of precipitation and wind turbulence. Temperature was also found to be significant with a peak at just below 16 degrees Celcius. Surprisingly, there was a significant positive impact of wind speed. The CAR model for the Pulicaris group also identified a significant attraction to the smaller groups of sheep placed in the field. Furthermore, a large number of spatial covariates which were incorrectly found to be significant in ordinary regression models were not significant in the CAR models. The 95% C.I. on the prediction estimates ranged from 20.4% to 304.8%, underlining the difficulties of predicting the abundance of Culicoides.ConclusionsWe found that significant spatial clusters of Culicoides moved around in a dynamic pattern varying between catch nights. This conforms with the modeling but was not explained by any of the tested covariates. The mean abundance within these clusters was up to 11 times higher for the Obsoletus group and 4 times higher for the Pulicaris group compared to the rest of the field.
Highlights
Biting midges, Culicoides, of the Obsoletus group and the Pulicaris group have been involved in recent outbreaks of bluetongue virus and the former was involved in the Schmallenberg virus outbreak in northern Europe
In a large scale study, Purse et al [18] found that the abundance of adult C. pulicaris sensu stricto was correlated with vegetation indices, land use and elevation above sea level; C. punctatus abundance was correlated with the presence of sheep, temperature, land use and vegetation; and the abundance of C. obsoletus was only correlated with temperature
No Culicoides emerged from the 350 random samples on the field, indicating that Pulicaris group breeding sites were confined to the identified breeding sites and that the Obsoletus group did not emerge on the field during the study period
Summary
Many large-scale studies and transmission models have included spatial estimates of the abundance of Culicoides in Europe ([7,8,9,10,11,12,13,14,15,16]), but few studies have investigated the spatial pattern of Culicoides abundance on a local scale: In 1951, Kettle [17] found that the abundance of C. impunctatus decreased proportionally with distance to their breeding sites This species is not dominant on farms but frequently associated with bogs In this study we take a novel approach, using local-scale abundance data to investigate possible spatial and temporal covariates for prediction of Culicoides abundance within a field
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
