Abstract
Control of tsetse flies using insecticide-treated targets is often hampered by vegetation re-growth and encroachment which obscures a target and renders it less effective. Potentially this is of particular concern for the newly developed small targets (0.25 high × 0.5 m wide) which show promise for cost-efficient control of Palpalis group tsetse flies. Consequently the performance of a small target was investigated for Glossina fuscipes fuscipes in Kenya, when the target was obscured following the placement of vegetation to simulate various degrees of natural bush encroachment. Catches decreased significantly only when the target was obscured by more than 80%. Even if a small target is underneath a very low overhanging bush (0.5 m above ground), the numbers of G. f. fuscipes decreased by only about 30% compared to a target in the open. We show that the efficiency of the small targets, even in small (1 m diameter) clearings, is largely uncompromised by vegetation re-growth because G. f. fuscipes readily enter between and under vegetation. The essential characteristic is that there should be some openings between vegetation.This implies that for this important vector of HAT, and possibly other Palpalis group flies, a smaller initial clearance zone around targets can be made and longer interval between site maintenance visits is possible both of which will result in cost savings for large scale operations. We also investigated and discuss other site features e.g. large solid objects and position in relation to the water's edge in terms of the efficacy of the small targets.
Highlights
The major vectors of Human African Trypanosomiasis (HAT) are in the Palpalis group tsetse flies, especially the G. fuscipes subspecies, which are responsible for transmission of .90% of reported HAT cases [1,2]
Small (0.2560.5 m) insecticide-treated targets have been shown to be cost-efficient for several Palpalis group tsetse flies, but there are concerns that they may become obscured by vegetation with a subsequent reduction in efficiency
We showed that the efficiency of the small targets was largely uncompromised by vegetation encroachment because G. f. fuscipes readily enter between and under vegetation to locate a small target, e.g. into small (1 m diameter) site clearings and underneath a very low (0.5 m) canopy
Summary
The major vectors of Human African Trypanosomiasis (HAT) are in the Palpalis group tsetse flies, especially the G. fuscipes subspecies, which are responsible for transmission of .90% of reported HAT cases [1,2]. In the present situation with limited drug and no vaccine availability, vector control remains an important addition to current efforts against HAT. Control of Palpalis group flies is costly and requires high densities of 10–30+ targets to be deployed per km. Morsitans group tsetse can be controlled with odour-baited targets at densities as low as 4per km2 [5,6,7]. If an odour is used with the device for control of Morsitans group flies, this range is about 5–150 m plus, while an unscented target or trap has a range of about 5–30 m [9]. Limited artificial odours exist at present for Palpalis group flies [10,11] so the trap or target’s efficacy relies heavily on its visibility
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