Abstract:
The efficacy of untreated and alphacypermethrin-treated high density polyethylene (HDPE) mesh
against Culicoides biting midges (Diptera: Ceratopogonidae) was determined using Onderstepoort
downdraught black light traps and a contact bioassay. Three traps were operated overnight in four
replicates of a 3 x 3 randomised Latin square design near horses under South African field conditions.
Both the untreated and alphacypermethrin-treated HDPE mesh significantly (P < 0.05) reduced the
numbers of Culicoides midges, predominantly Culicoides (Avaritia) imicola Kieffer, collected in the
light traps by 4.2 and 7.2 times respectively. A repellent effect of the alphacypermethrin-treated mesh
was not confirmed because the number of midges collected in the light traps with untreated and
alphacypermethrin-treated HDPE mesh were not significantly different (P = 0.656). Bioassay of the
insecticidal contact efficacy indicated median C. imicola mortality of 100% from 30 and 10 min
following exposure to the alphacypermethrin-treated HDPE mesh for 1 or 3 min, respectively. In the
bioassay, mortality was significantly higher (P = 0.016) at 5 min post exposure in the midges exposed
to the alphacypermethrin-treated mesh for 3 min (74.8%) compared to the 1 min exposure group
(59.5%). The HDPE mesh could be used to reduce exposure of housed animals to Culicoides midges,
specifically C. imicola, and viruses transmitted by these midges. Mesh treated with alphacypermethrin
had the additional benefit of a rapid insecticidal effect on C. imicola.
