Rapid assessment of widespread aerial spraying of deltamethrin for tsetse fly control on non-target insects in the Okavango Delta, Botswana

Full text: Recent advances in satellite navigation technology make it possible for aerial application of insecticides to cover wide areas without leaving pockets of habitat unsprayed. The Government of Botswana decided that such a programme using deltamethrin would be undertaken in 2001 and 2002 to tackle the troublesome and longstanding infestation of tsetse fly (Glossina mortisans) in the Okavango Delta in northern Botswana. The objective in removing tsetse was to improve public health and cattle production whilst minimising environmental impact. The Government of Botswana immediately commissioned an environmental impact appraisal for the spraying project and allocated significant funds to an environmental monitoring programme to assess and report on the effects of spraying. A key challenge was how to assess impacts of blanket tsetse control on non-target insects that were numerous, integral to many ecosystem services, potentially susceptible to the insecticide, poorly known and difficult to sample. At selected sites, invertebrates were sampled from three tree species, Kigelia africana, Combretum imberbe and Lonchocarpus capassa, by fogging individual tree canopies with deltamethrin prior to any aerial spray applications. This provided a benchmark estimate of canopy invertebrates before the spray. Then invertebrates were collected from beneath these and non-fogged trees during each spray cycle (knockdown) and at the end of the aerial spraying programme selected trees were fogged again. This allowed us to determine what invertebrates were present before, during and after the aerial spray cycles and provide an accurate estimate of impact. In 2003 the same trees were revisited and invertebrates sampled by fogging the canopies of previously fogged and unfogged trees. Comparisons of abundance and composition were made to see if susceptible taxa of beetles, flies, spiders, Hemiptera and ants had made a recovery to previous levels and to see if any species had been lost or depleted. This paper reports some of the impacts and recovery of these terrestrial invertebrates in tree canopies within the Okavango Delta using the biotrack system. This ecological and information technology solution to the taxonomy and data management was needed to accurately report on information from more than 150,000 specimens, 800 samples and 370 morphospecies identified. The outcome was a capacity to accurately report on the impact of large scale aerial spraying on non-target organisms. (author)