Environmental drivers of Culicoides phenology: how important is species-specific variation when determining disease policy?
Since 2006, arboviruses transmitted by Culicoides biting midges (Diptera: Ceratopogonidae) have caused significant disruption to ruminant production in northern Europe. The most serious incursions involved strains of bluetongue virus (BTV), which cause bluetongue (BT) disease. To control spread of BTV, movement of susceptible livestock is restricted with economic and animal welfare impacts. The timing of BTV transmission in temperate regions is partly determined by the seasonal presence of adult Culicoides females. Legislative measures therefore allow for the relaxation of ruminant movement restrictions during winter, when nightly light-suction trap catches of Culicoides fall below a threshold (the 'seasonally vector free period': SVFP). We analysed five years of time-series surveillance data from light-suction trapping in the UK to investigate whether significant inter-specific and yearly variation in adult phenology exists, and whether the SVFP is predictable from environmental factors. Because female vector Culicoides are not easily morphologically separated, inter-specific comparisons in phenology were drawn from male populations. We demonstrate significant inter-specific differences in Culicoides adult phenology with the season of Culicoides scoticus approximately eight weeks shorter than Culicoides obsoletus. Species-specific differences in the length of the SVFP were related to host density and local variation in landscape habitat. When the Avaritia Culicoides females were modelled as a group (as utilised in the SFVP), we were unable to detect links between environmental drivers and phenological metrics. We conclude that the current treatment of Avaritia Culicoides as a single group inhibits understanding of environmentally-driven spatial variation in species phenology and hinders the development of models for predicting the SVFP from environmental factors. Culicoides surveillance methods should be adapted to focus on concentrated assessments of species-specific abundance during the start and end of seasonal activity in temperate regions to facilitate refinement of ruminant movement restrictions thereby reducing the impact of Culicoides-borne arboviruses.
Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian, United Kingdom.
Kate R
KR
Searle
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
James
J
Barber
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Francesca
F
Stubbins
PVVD, ARC-Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort, South Africa.
Karien
K
Labuschagne
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Simon
S
Carpenter
Biomathematics and Statistics Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh, United Kingdom.
Adam
A
Butler
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Eric
E
Denison
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Christopher
C
Sanders
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Philip S
PS
Mellor
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Anthony
A
Wilson
The Met Office, Based at The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom.
Noel
N
Nelson
The Pirbright Institute, Ash Road, Pirbright, Woking, United Kingdom.
Simon
S
Gubbins
Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian, United Kingdom.
Bethan V
BV
Purse
D000818:Animals; D001102:Arbovirus Infections / Q000662:veterinary*; D002519:Ceratopogonidae; D004777:Environment; D005260:Female; D006291:Health Policy; D007300:Insect Control; D007303:Insect Vectors; D008297:Male; D012418:Ruminants; D013045:Species Specificity