Standardizing visual control devices for tsetse flies: East African species Glossina swynnertoni

Abstract

Background: Here we set out to standardize long-lasting, visually-attractive devices for Glossina swynnertoni, a vector of both human and animal trypanosomiasis in open savannah in Tanzania and Kenya, and in neighbouring conservation areas used by pastoralists. The goal was to determine the most practical device/material that would induce the strongest landing response in G. swynnertoni for use in area-wide population suppression of this fly with insecticide-impregnated devices.

Methods and findings: Trials were conducted in wet and dry seasons in the Serengeti and Maasai Mara to measure the performance of traps 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 simple enumerator at these remote locations to compare trapping efficiencies of devices. Independent of season or presence of chemical baits, targets in phthalogen blue or turquoise blue cloth with adhesive film were the best devices for capturing G. swynnertoni in all situations, catching up to 19 times more flies than pyramidal traps. Baiting with chemicals did not affect the relative performance of devices. Fly landings were two times higher on 1 m(2) blue-black targets as on pyramidal traps when equivalent areas of both were covered with adhesive film. Landings on 1 m(2) blue-black targets were compared to those on smaller phthalogen blue 0.5 m(2) all-blue or blue-black-blue cloth targets, and to landings on all-blue plastic 0.32-0.47 m(2) leg panels painted in phthalogen blue. These smaller targets and leg panels captured equivalent numbers of G. swynnertoni per unit area as bigger targets.

Conclusions: Leg panels and 0.5 m(2) cloth targets show promise as cost effective devices for management of G. swynnertoni as they can be used for both control (insecticide-impregnated cloth) and for sampling (rigid plastic with insect glue or adhesive film) of populations.

Figure 1. Blue cotton target with adhesive film and adjoining adhesive film target in Serengeti tsetse habitat.

Figure 2. Detransformed daily trapping rates for G. swynnertoni by unbaited and POCA-baited visual devices.

trap pyramidal trap, target 1.5 m² target, leg panel local panels (0.47 m² Tanzania, 0.32 m² Kenya), std standard phthalogen blue, turq turquoise blue, blue pl blue-painted plastic (0.45 m²), unbaited no baits, baited baited with POCA, dtr. mean detransformed mean. POCA is a 1∶4∶8 mixture of 3-n-propylphenol (P), 1-octen-3-ol (O), and p-cresol (C) released from a polyethylene sachet and acetone (A) released from a bottle. 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.

Figure 3. Daily catches of G. swynnertoni and G. pallidipes by devices with and without adhesive film.

pyramidal pyramidal trap; target blue-black 1 m² target. 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.

Figure 4. Daily catches of G. swynnertoni and G. pallidipes with different target types.

Targets were all blue, or of equal vertical rectangles of blue and black or blue-black-blue material. Devices were covered with adhesive film to compare the propensity of flies to land on the different target types. 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.