Local dispersal of palaearctic Culicoides biting midges estimated by mark-release-recapture.

Georgette Kluiters,Matthew Baylis,Harry Swales

doi:10.1186/s13071-015-0658-z

Abstract

BackgroundFarm to farm movement of Culicoides midges is believed to play a critical role in the spread of bluetongue (BT), Schmallenberg and other midge-borne diseases. To help understand and predict the spread of diseases carried by midges, there is a need to determine their dispersal patterns, and to identify factors contributing to the direction taken and distance travelled.MethodsThe dispersal of Obsoletus Group members was studied on 19 farms around Bala, north Wales. Field-collected Culicoides were trapped in a black-light (OVI) trap and self-marked in the collecting vessel, using micronized fluorescent dust. Culicoides were released at a central farm and OVI traps set on 18 surrounding farms, at distances of 1 to 4 km. The study was repeated using six colours of fluorescent dust over an 18 day period.ResultsAn estimated 61,062 (95% CI = 56,298-65,830) marked Culicoides were released during the study and 12 (0.02%) Culicoides were recaptured. Of the females recaptured, six were C. obsoletus/scoticus, two C. dewulfi, two C. pulicaris and one C. festivipennis. The male was C. obsoletus. Recaptures occurred 1–2.5 km from the release site, with greatest numbers at 2.5 km. Most recaptures were 2 nights post-release; none were more than 3 nights post-release. Two females were recovered at 1.5 km on the night of release and one male at 1 km two nights post-release. The mean distance travelled (MDT) for males was 1 km, females was 2.21 km, and all recaptured Culicoides was 2.15 km. Recaptures were made both downwind and upwind of the prevailing wind direction during the trapping periods, highlighting possible passive and active dispersal of Culicoides between farms.ConclusionsThis is the first study to demonstrate farm to farm movement of the main Palaearctic BT vector species, the Obsoletus Group. Such movement has disease control implications in terms of the vectoral movement of disease between farms. The results suggest that Culicoides control measures applied at an infected farm (trapping or killing Culicoides) will reduce risk of spread to neighbouring farms by lessening the number of Culicoides dispersing from that farm, as well as reducing transmission at the source farm itself.

Highlights

Farm to farm movement of Culicoides midges is believed to play a critical role in the spread of bluetongue (BT), Schmallenberg and other midge-borne diseases
Modelling of disease outbreaks suggests that longrange dispersal over land is not a common phenomenon and does not contribute to the spread of arbovirus disease [4,5], with the majority of bluetongue cases occurring within 5 km of the previous case during the 2006 European BT outbreak [6]
Marking method Marked midges remained distinguishable for their entire life; dusts did not transfer from marked to unmarked individuals or the environment; the mortality rate of marked midges did not differ from controls under laboratory conditions; and, importantly for trapping and storing Culicoides, the dust did not dissolve or wash off in either ethanol or water

Summary

Introduction

Farm to farm movement of Culicoides midges is believed to play a critical role in the spread of bluetongue (BT), Schmallenberg and other midge-borne diseases. To help understand and predict the spread of diseases carried by midges, there is a need to determine their dispersal patterns, and to identify factors contributing to the direction taken and distance travelled. Since its emergence in northern Europe, bluetongue (BT) has spread to regions where the main Mediterranean vector species, Culicoides imicola Kieffer, is absent. Kluiters et al Parasites & Vectors (2015) 8:86 during a set period; and to identify factors that contribute to the direction and flight distance. Very few studies have investigated short distance Culicoides dispersal, with the most recent work undertaken in 2010 in Denmark [8], followed by work in the US in the 1980s [8,9,10]. A large number of insects are trapped and mass-marked before being released at a central location and an attempt made to recapture those individuals at known distances from the release site

Methods

Results

Discussion

Conclusion