Insecticide-treated mesh in stables effective in curbing midges – study

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The stable type used in the second field trial to investigate the effectiveness of insecticide-treated mesh.
The stable type used in the second field trial to investigate the effectiveness of insecticide-treated mesh.

Insecticide applied to insect mesh screens in a British study proved effective at preventing biting midges from entering stables holding horses.

Biting midges of the genus Culicoides Latreille, 1809 (Diptera: Ceratopogonidae) cause a significant biting nuisance to horses and are responsible for transmission of African horse sickness virus.

While the virus is currently restricted to sub-Saharan Africa, it has a history of emerging in southern Europe.

In the event of an outbreak, several authorities have recommended the use of insecticide-treated nets to screen stables to keep the midges away from horses.

The research team set out to assess whether this was effective, noting that the creation of truly vector-proof accommodation was rarely attempted due to the costs involved and the difficulties in accurately monitoring potential lapses in biosecurity.

Lara Ellen Harrup and her colleagues first assessed seven commercially available pyrethroid insecticides and three repellent compounds, all licensed for amateur use, against Culicoides nubeculosus (Meigen), 1830.

Only one, a product called Tri-Tec 14 exhibited 100% mortality on batches of C. nubeculosus following a three-minute exposure at 1, 7 and 14 days post-treatment in a laboratory-based test. It was subsequently selected for the next stage of the study.

Two summer field trials were conducted at a polo club in Hampshire to test the efficiency of treated net screens in preventing entry of Culicoides midges.

The researchers, whose findings have been published in the journal Parasites & Vectors, applied the product – a formulation of cypermethrin (0.15% by weight) and pyrethrins (0.2% by weight) – to black polyvinyl-coated polyester insect screen.

The equipment used to investigate the effectiveness of insecticide-treated mesh in the first field trial.
The equipment used to investigate the effectiveness of insecticide-treated mesh in the first field trial.

The screen was 1.6mm thick and had apertures that were 1.6mm wide. The treated mesh was used around an ultraviolet light trap (pictured above), and a series of nightly collections were made. It entirely prevented Culicoides midges being collected, despite their successful collection in identical traps with untreated screening or no screening at all.

The second field trial examined entry of the midges into stables containing horses, in which treated mesh was afixed over stable openings. It was found that while the insecticide-treated screens reduced entry substantially, there was still a small risk of exposure to biting.

Screened stables can be used as part of an integrated control program in the event of an African horse sickness virus outbreak in order to reduce contact between the midges and horses in stables, the authors concluded. It might also be applicable to protecting horses from biting midges during transport.

Discussing their findings, the researchers said the use of untreated mesh to screen stables had previously been shown to provide a degree of protection to equines from Culicoides midges.

They noted that all insecticide-based treatments tested within the study contained either cypermethrin, pyrethrins, permethrin, tetramethrin or a combination of these compounds.

Systematic comparison of the active ingredients would help product development, they suggested.

“An obvious omission to the above list is any insecticide based on deltamethrin, which has demonstrated high toxicity to C. obsoletus in Spain and France in laboratory exposure assays to treated filter papers, but is not currently available in the UK in a formulation available for amateur use.”

Harrup is with the Pirbright Institute. She was joined in the study by Simon Carpenter and Simon Gubbins, also from the institute; Tiffany Baker, from the University of Surrey; Richard Newton, from the Animal Health Trust; and Giovanni Lo Iacono, from the University of Cambridge

Can insecticide-treated netting provide protection for Equids from Culicoides biting midges in the United Kingdom? 
Tiffany Baker, Simon Carpenter, Simon Gubbins, Richard Newton, Giovanni Lo Iacono, James Wood and Lara Ellen Harrup.
Parasites & Vectors20158:604 DOI: 10.1186/s13071-015-1182-x
The full study can be read here
The study was published under a Creative Commons License.

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