Abstract
The impact of topical applications of deltamethrin and ivermectin to cattle on Culicoides spp. landing and blood-feeding was studied in this work using sticky traps mounted on Friesian heifers’ backs. There was no effect of the insecticides on total numbers of Culicoides trapped or the proportion engorged. Deltamethrin and ivermectin treatment did not prevent blood-feeding on these animals. Deltamethrin did result in significant Culicoides mortality as evidenced by the numbers of dead midges combed from heifers’ upper flanks. The proximity of engorged midges on traps to dead midges in the hair suggests that blood-feeding took place despite midges receiving an ultimately lethal dose of deltamethrin. Ivermectin application resulted in a smaller proportion of nulliparous than parous females caught. There was no significant effect of ivermectin on the numbers of Culicoides that emerged from dung samples (but p was small at 0.095 for the Obsoletus group Culicoides). In cases of suspect animal imports, pour-on or spray applications of deltamethrin could reduce the risk of onward transmission of bluetongue virus.
Highlights
Biting midges, Culicoides spp. (Diptera: Ceratopogonidae), are important vectors of viral pathogens of livestock
There was no effect of deltamethrin or ivermectin treatment on the number of Culicoides caught on sticky traps (overall Culicoides per heifer, back-transformed (b-t) from generalized linear mixed models (GLMMs) predictions with 95% confidence intervals: Obsoletus group −
The main result from this study is that neither deltamethrin nor ivermectin prevented blood-feeding by Culicoides midges on cattle in a field situation
Summary
Culicoides spp. (Diptera: Ceratopogonidae), are important vectors of viral pathogens of livestock. Whilst vaccination was the ultimate solution to the bluetongue outbreak, at early stages of a disease outbreak vaccines may not be developed or available in sufficient quantities for disease management At these crucial early stages, vector control is a valuable option to prevent spread of the disease [1]. The infected heifer was euthanized and the other animals quarantined This was during the ‘vector-free’ period as defined by fewer than five parous Culicoides per light trap catch [4], but small numbers of midges were still flying. In cases such as this, insecticide application could reduce the likelihood of onward transmission of the pathogen
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