Field and in vitro insecticidal efficacy of alphacypermethrin-treated high density polyethylene mesh against Culicoides biting midges in South Africa.

The research in question investigates how effective different types of high-density polyethylene (HDPE) mesh, either untreated or treated with the insecticide alphacypermethrin, are in controlling populations of Culicoides biting midges in South Africa. The results demonstrated that both varieties of mesh resulted in a decrease in midge numbers, though the insecticide-treated mesh had the added advantage of instantly killing the insects upon contact.

Methodology and Experiment Design

• The researchers set up Onderstepoort downdraught black light traps and a contact bioassay to measure the effectiveness of the HDPE mesh. These traps were operated overnight in different sets of three, structured around a randomised Latin square design.
• The experiments were conducted in areas near horses under field conditions representative of those found in South Africa to ensure the findings are applicable to real-world scenarios.

Key Findings

• The study found that both the untreated and alphacypermethrin-treated HDPE mesh resulted in a significant decrease in the numbers of Culicoides midges, with the latter reducing numbers by a slightly larger factor.
• However, the supposed repellent effect of the alphacypermethrin-treated mesh was not confirmed, as the number of midges collected in the light traps was essentially the same for both types of mesh.
• When tested for insecticidal contact, the alphacypermethrin-treated HDPE mesh induced a mortality rate of 100% in C. imicola midges from 30 and 10 minutes following exposure for 1 or 3 minutes, respectively. Furthermore, mortality was higher when the exposure time to the treated mesh was increased from 1 to 3 minutes.

Implications and Conclusions

• The study suggests that HDPE mesh, with or without insecticidal treatment, can be used as a strategy to reduce exposure of certain livestock, like horses, to harmful Culicoides midges and the viruses they carry.
• Mesh treated with alphacypermethrin was confirmed to have a swift insecticide effect on C. imicola, one of the prevalent species of midges in the region.