Pilot study on investigating the current status and changes in the pest blackfly (Diptera: Simuliidae) problem on the Orange
Blackfly along the middle and lower reaches of the Orange River are major pests of livestock and labour-intensive agriculture, with losses to the industry calculated to exceed R300 million per annum based on current meat prices. The problem is attributed to winter high flows, with the main pest species being Simulium chutteri Lewis although there are times when S. damnosum s.l. Theobald and S. impukane de Meillon are problematic. During 2011, blackfly outbreaks in the middle and lower reaches of the Orange River were noted to have worsened. It was proposed that current reduced success in controlling S. chutteri using larvicides could be one of the reasons for this. Alternatively, or additionally, outbreaks may have been due to other species of blackfly not being targeted for control, particularly S. impukane. This study utilized a combination of published data, empirical field surveys, and experiments to investigate the likelihoods of these competing reasons, and to propose control options. Based on the combined evidence, it is unlikely that the outbreaks experienced during 2011 were the result of another species of blackfly additional to S. chutteri. The best avenues for improved blackfly control should focus on (1) management issues around the control programme itself, as previously highlighted by Palmer et al. (2007), and (2) hydraulic studies linked to investigations of downstream carry of larvicides in the anastomosing sections, which are likely to be the least well controlled areas on the middle Orange River. However, while it is unfortunate that these sections are associated with human settlement areas, it is also important to bear in mind that residual populations of different species of blackfly should be maintained in the range river as parts of its natural ecological functioning, and that the anastomosing sections could be serving a role as refugia.
- Pilot study on investigating the current status and changes in the pest blackfly (Diptera: Simuliidae) problem on the Orange. Water Research Commission Project No K8/1004.
- Rivers-Moore NA, Palmer RW & Dallas HF. 2014. Assessing the relative culpability of Simulium (Diptera: Simuliidae) species in recent black fly outbreaks along the middle Orange River, South Africa. Can. J. Zool. 92: 505–513 (2014) dx.doi.org/10.1139/cjz-2014-0008.