Are insecticide-treated cattle better than targets?

A single insecticide-treated ox kills about as many tsetse as a single odour-baited target. So if there are already many cattle in an area, then treating cattle appears to offer several advantages over using targets.

First, treating an animal is cheaper than constructing and deploying an insecticide-treated target.

Second, cattle owners are strongly inclined to treat their cattle with insecticide, maintain them and protect them from theft. So several problems associated with using targets - such as the loss of targets due to general wear and tear, theft, and animal damage - are less with insecticide-treated cattle.

So is there any point in using targets?

The problem with insecticide-treated cattle is that they tend to be confined to certain areas. Indeed, farmers will often avoid grazing their cattle where tsetse are abundant, and the imperatives of finding adequate water and grazing further limit their distribution. Cattle are also generally grouped into herds, and a group of ten cattle does not kill ten times as many tsetse as a single animal. In fact, a herd of ten cattle will only kill about three times as many tsetse as a single animal. The upshot of this is that densities of four cattle per square kilometre are generally not sufficient to control savanna species of tsetse, whereas this density of targets is. The crucial difference is that we can deploy targets in an even manner, and in areas where tsetse are abundant. So targets have a very important role to play, even in areas where cattle are present.

Most tsetse control strategies will require a combination of insecticide-treated cattle and targets, with the latter being used to plug the inevitable gaps in the local distribution of cattle.