The repellent effect of organic fatty acids on Culicoides midges as determined with suction light traps in South Africa

The efficacy of a 15% (w/w) mixture of octanoic, nonanoic and decanoic acids in light mineral oil to repel Culicoides biting midges (Diptera; Ceratopogonidae) was determined in three replicates of a 4 × 4 Latin square design under South African field conditions. The fatty acids were applied to ±0.07 m2 polyester meshes with a mesh size 2-3 mm fitted to 220 V 8 W Onderstepoort downdraught light traps. To reduce the relatively strong attraction of the light trap, the black light tubes in the Onderstepoort trap were replaced with 8 W 23 cm white light tubes. The traps were operating overnight next to cattle. Two traps treated with the mixture of fatty acids collected 1.7 times fewer midges than two untreated traps. Although this mixture of fatty acids had shown a repellent effect against a number of blood-feeding insects this is the first indication that it also has a significant repellent effect against Culicoides species and especially Culicoides (Avaritia) imicola Kieffer when applied to polyester mesh.