Methods for dispensing odour attractants for tsetse flies (Diptera: Glossinidae)

Methods for dispensing tsetse attractants using sealed polyethylene sachets and bottles were studied in the laboratory and field. 1-Octen-3-ol (octenol), 4-methylphenol and 3-n-propylphenol were dispensed singly or as blends from sachets 25–200 cm2 in surface area and with a wall thickness of 0.06–0.32 mm; butanone was dispensed from polyethylene bottles. The release rates of attractants, assessed gravimetrically or by GC analysis of volatiles released, were independent of the amount present. The rates were related directly to surface area, inversely related to wall thickness and increased exponentially with temperature. With blends of the attractants, the release rates of the two phenols were directly proportional to the concentration present, but that of octenol showed an exponential dependence. A similar exponential effect was seen with blends of the attractants and an involatile diluent. For mixtures of chemicals, the ratio of the released components was not affected significantly by temperature, sachet size or wall thickness. Release rates from polyethylene sachets and bottles in the field varied 100-fold according to temperature differences related to the time of day, season, and degree of insolation. Day-degree models to predict the losses of attractants from a polyethylene sachet in shade or in full sunlight were highly correlated (r2 = 0.84 and 0.81 respectively) with observed losses. The practical implications of these findings are discussed.

Responses of tsetse flies (Diptera: Glossinidae) to natural and synthetic ox odours

In Zimbabwe, studies were made of the levels of known tsetse attractants present in natural ox odour. Typically an ox (400 kg) produced phenol (0.1 mg/h), 3-methylphenol (0.09 mg/h), 4-methylphenol (0.7 mg/h), 3-ethylphenol (0.01 mg/h), 4-ethylphenol (0.02 mg/h), 3- and 4-n-propylphenol (0.02 mg/h), l-octen-3-ol (0.01 mg/h), carbon dioxide (140 l/h), acetone (5 mg/h) and butanone (0.3 mg/h). Of these, only phenol, 4- and 3-methylphenol and carbon dioxide were always detected in ox odour. Studies were made of the numbers of Glossina pallidipes Austen and G. morsitans morsitans Westwood attracted to natural ox odour and synthetic odour, the latter consisting of blends of identified attractants dispensed at the doses naturally present in ox odour. Natural ox odour caught twice (P < 0.05) as many G. pallidipes and 1.5 (P < 0.05) times as many G. m. morsitans as the synthetic blend suggesting the presence of an unidentified attractant in ox odour. Passing ox odour through filters indicated that all attractants can be trapped on a combination of charcoal and sodalime filters but the unidentified attractant(s) may pass through a sodalime filter, and break through a charcoal filter used for more than 6 h. Increasing the dose of ketones in the synthetic odour from 2 to 100 mg/h doubled the catches at the source. Increases in ketone levels in hosts, induced by starvation or possibly trypanosomiasis, may increase attraction of tsetse to such animals.

Responses of Glossina morsitans morsitans Westwood and G. pallidipes Austen (Diptera: Glossinidae) to the skin secretions of oxen

In Zimbabwe, catches of Glossina morsitans morsitans Westwood and G.pallidipes Austen at odour baited traps were increased in the presence of residues of a solution of the skin secretions of oxen (hereafter sebum) by 80% and 29% respectively, and catches at F3 traps were significantly increased when sebum was presented on adjacent screens. Testing of fractions of sebum revealed active components(s) in the phenolic and non-acidic fractions but not in the acidic fraction. Furthermore, the activity of the phenolic fraction could not be explained by the presence of the known phenolic tsetse attractants. The effect of sebum was to attract more flies to the target rather than to induce a landing response in a higher proportion of attracted flies. Whether or not tarsal contact responses are involved remains conjectural. However, targets that were electrified over only one quarter of the surface caught more than one quarter the catch of targets electrified over all the surface both with and without sebum, indicating that many tsetse habitually alight more than once on baited targets. Data on the catches of other Diptera are also presented