Trials of compounds to enhance trap catches of Glossina palpalis palpalis in Liberia

Medical and Veterinary Entomology (1988) 2, 199-200

SHORT C O M M U N I C A T I O N

Trials of compounds to enhance trap catches of Glossina palpalis palpalis in Liberia R. A. CHEKE and R. G A R M S * Overseas Development Natural Resources Institute, London, a n d *Bernhard-Nocht Institut fur Schiffs- und Tropenkrankheiten, Hamburg

Key words. Tsetse, Glossinapalpalis, traps, olfactory attractants, Liberia.

Acetone, 1-octen-3-ol and various phenolic compounds have been shown to be components of host odours attractive to the savanna tsetse species Glossina morsitans morsitans Westwood and G.pallidipes Austen in Zimbabwe (Vale & Hall, 1985a, b; Bursell et al., 1988; Vale et al., 1988) and to G.pallipides in Kenya (Hassanali et al., 1986; Dransfield et al., 1986). Acetone and 1-octen-3-01 have also been found to increase trap catches of G.m.submorsitans in Burkina Faso (Politzar & Merot, 1984). In this report we describe trials of the effects of such compounds on trap catches of G.palpalis palpalis (Robineau-Desvoidy) in forest habitats in Liberia. Carbon dioxide is the only olfactory attractant known to date for the G.palpalis group (WHO, 1986). The trials were conducted from July to September 1986 at three sites beside the St ,Paulriver near Haindi (6” 54’N, 10”23’W) and at one site beside the Men creek (6” 56‘N, 10”IS’W), using biconical traps (Challier & Laveissikre, 1973). The attractants tested were acetone, l-octen3-01 and ‘TF86/05’, a mixture of phenols found in cattle urine that has been shown to increase catches of G.pal1idipe.s in traps baited with acetone and 1-octen-3-01in Zimbabwe (Vale et al., 1988). ‘TF 86/05’ contains phenol (1.4 parts relative to concentration of 4-methylphenol), 3-methylphenol (9.9), 4-methylphenol (loo), 3-ethylphenol (1.1),4-ethylphenol (2.1), 3-propylphenol (2.5), 4-propylphenol (0.8) and 2-methoxyphenol (0.4). For tests involving ‘TF 86/05’, a drop of the mixture was allowed to Correspondence: Dr R. A. Cheke, Overseas Development Natural Resources Institute, College House, Wrights Lane, London W8 5SJ.

evaporate from an open-topped glass vial (diameter of opening 6 mm): the acetone and 1-octen-3-01 were dispensed at 100 mg h-* and 0.5 mg h-l, respectively, as described by Vale & Hall (1985a). In each case the vials containing the compounds were attached with sticking plaster to the central pole of the traps, 1&15 crn below the base of the cloth section. Baited traps and unbaited controls were tested simultaneously in pairs, with the traps 20-50 m apart. The distance was not standardized because of the lack of available space in the thick forest beside the rivers. During each trial the trap pairs were in place from 08.00 to 16.00 hours. The position of the baited trap was alternated for each replicate. In addition on nine occasions pairs of traps were tested, as controls, with no baits at all. In these trials a mean of 13.7 (range2-47, SD=12.8, n=18) G.p.palpalis were caught per trap. The results of experiments with baited traps, each paired with an unbaited control, are summarized in Table 1. On average, twice as many G.p.palpalis were caught in traps baited with acetone or 1-octen-3-01as in controls. The differences were significant when the results of each pair of traps were analysed by the Wilcoxon matched pair signed rank test. No evidence was found for attraction by ‘TF 86/05’ nor for a combination of all three chemical baits. Some G.pallicera Bigot were also caught during the experiments, but too few (twenty) for any effects to be discernible. Traps baited with ‘TF 86/05’ caught relatively more female G.p.palpalis than any others and those baited with acetone or 1-octen-3-01caught proportionately more males than their controls 199

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R . A. Cheke and R . Garms

TABLE 1. Comparison between catches of Glossinap.palpalis in baited and unbaited traps. Levels of significance were tested by the Wilcoxon matched pair signed rank test. Baited traps Compound

Unbaited traps Mean no. of flies

Range

Sex ratio

d/?

(3 1. Acetone 21.3 2. 1-octen-3-01 25.0 12.6 3. “IF 86/05’ 4. 1+2+3 10.3

Mean no. of flies

Range

0.61 0.70 0.39 0.63

11.1 12.1 11.8 11.0

No. of replicates

No. of replicates when baited trap caught most flies

Level of significance P

11 9 5 6

10 7 3