Standardising Visual Control Devices for Tsetse Flies: Central and West African Species <i>Glossina palpalis palpalis</i>

Background: Glossina palpalis palpalis (G. p. palpalis) is one of the principal vectors of sleeping sickness and nagana in Africa with a geographical range stretching from Liberia in West Africa to Angola in Central Africa. It inhabits tropical rain forest but has also adapted to urban settlements. We set out to standardize a long-lasting, practical and cost-effective visually attractive device that would induce the strongest landing response by G. p. palpalis for future use as an insecticide impregnated tool in area-wide population suppression of this fly across its range. Methodology/Principal Findings: Trials were conducted in wet and dry seasons in the Ivory Coast, Cameroon, the Democratic Republic of Congo and Angola to measure the performance of traps (biconical, monoconical and pyramidal) and targets of different sizes and colours, with and without chemical baits, at different population densities and under different environmental conditions. Adhesive film was used as a practical enumerator at these remote locations to compare landing efficiencies of devices. Independent of season and country, both phthalogen blue-black and blue-black-blue 1 m2 targets covered with adhesive film proved to be as good as traps in phthalogen blue or turquoise blue for capturing G. p. palpalis. Trap efficiency varied (8–51%). There was no difference between the performance of blue-black and blue-blackblue 1 m2 targets. Baiting with chemicals augmented the overall performance of targets relative to traps. Landings on smaller phthalogen blue-black 0.25 m2 square targets were not significantly different from either 1 m2 blue-black-blue or blue-black square targets. Three times more flies were captured per unit area on the smaller device. Conclusions/Significance:Blue-black 0.25 m2 cloth targets show promise as simple cost effective devices for management of G. p. palpalis as they can be used for both control when impregnated with insecticide and for population sampling when covered with adhesive film

Standardising visual control devices for Tsetse: East and Central African Savannah species Glossina swynnertoni, Glossina morsitans centralis and Glossina pallidipes.

BACKGROUND:This study focused on the savannah tsetse species Glossina swynnertoni and G. morsitans centralis, both efficient vectors of human and animal trypanosomiasis in, respectively, East and Central Africa. The aim was to develop long-lasting, practical and cost-effective visually attractive devices that induce the strongest landing responses in these two species for use as insecticide-impregnated tools in population suppression. METHODS AND FINDINGS:Trials were conducted in different seasons and years in Tanzania (G. swynnertoni) and in Angola and the Democratic Republic of the Congo (DRC, G. m. centralis) to measure the performance of traps (pyramidal and epsilon) and targets of different sizes, shapes and colours, with and without chemical baits, at different population densities and under different environmental conditions. Adhesive film was used to catch flies landing on devices at the remote locations to compare tsetse-landing efficiencies. Landing rates by G. m. centralis in both Angola and the DRC were highest on blue-black 1 m2 oblong and 0.5 m2 square and oblong targets but were not significantly different from landings on the pyramidal trap. Landings by G. swynnertoni on 0.5 m2 blue-black oblong targets were likewise not significantly lower than on equivalent 1 m2 square targets. The length of target horizontal edge was closely correlated with landing rate. Blue-black 0.5 m2 targets performed better than equivalents in all-blue for both G. swynnertoni and G. m. centralis, although not consistently. Baiting with chemicals increased the proportion of G. m. centralis entering pyramidal traps. CONCLUSIONS:This study confirms earlier findings on G. swynnertoni that smaller visual targets, down to 0.5 m2, would be as efficient as using 1 m2 targets for population management of this species. This is also the case for G. m. centralis. An insecticide-impregnated pyramidal trap would also constitute an effective control device for G. m. centralis

Detransformed mean daily catches of <i>G. palpalis palpalis</i> on targets with and without adhesive film.

<p>Asterisks indicate that the indices are significantly different from unity:</p><p>P≤0.01,</p><p>P≤0.001,</p><p>n/s not significant (P>0.05) following Tukey post hoc test.</p

Daily catches of <i>G. palpalis palpalis</i> by devices with and without adhesive film. Pyramidal

<p>pyramidal trap; <b>monoconical</b> monoconical trap; <b>target</b> blue-black 1 m² target. <b>dtr. mean</b> detransformed mean. The target and the cloth portions of traps were covered with adhesive film to compare the propensity of flies to land on the different devices. Catch rates of traps are divided into fly catches on the cloth part and those trapped in the cage of the trap. The limits of the boxes indicate the twenty-fifth and seventy-fifth percentiles, the solid line in the box is the median, the capped bars indicate the tenth and the ninetieth percentiles, and data points outside these limits are plotted as circles.</p

Catches^* of <i>G. palpalis palpalis</i> with unbaited and POCA-baited trapping devices in different blue fabrics.

<p>Detransformed mean daily catches.</p><p>Means followed by the same letter (a, b or c) are not significantly different (Tukey post hoc test, P = 0.05).</p

Participating countries in Central and West Africa; distribution of <i>Glossina palpalis</i>[57].

<p>Participating countries in Central and West Africa; distribution of <i>Glossina palpalis</i><a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002601#pntd.0002601-ORSTOMCIRADEMVT1" target="_blank">[57]</a>.</p

Pyramidal trap and regular 1² blue-black target with adhesive film in gallery forest, Tabi, Angola.

<p>Pyramidal trap and regular 1² blue-black target with adhesive film in gallery forest, Tabi, Angola.</p

Trap efficiency for <i>G. palpalis palpalis</i> calculated from detransformed mean daily catches^*.

<p><i>Total catch - flies landing on trap and caught in cage.</i></p