| dc.description.abstract | This study was conducted in order to develop an appropriate dispenser for the
waterbuck-derived repellent for tsetse flies. The waterbuck-derived repellent consisted of
pentanoic, hexanoic and heptanoic acids, guaiacol, geranylacetone, 2-undecanone and 8-
octalactone. The reservoir tube of the dispenser was made from aluminium (or
polypropylene) of diameter 10 rom and length 10 em. The diffusion area was made from
tygon silicon tubing of internal diameter 6.4 rom, outer diameter 9.6 mm, thickness 3.2
mm and length 2 em (diffusion area 6.028 cnr') or 4 em (diffusion area 12.056 crrr').
Preliminary trials were conducted under semifield conditions with a synthetic
repellent (2-methoxy-4-methyl phenol) to determine the effect of surface area on the
release rates. The rates were found to be directly related to the surface area of the tygon
tubing. Increasing the surface area increased the weight loss of 2-methoxy-4-methyl
phenoL These trials enabled the selection of appropriate lengths of the tubing to be used
in both the laboratory and semifield trials with the waterbuck-derived repellent blend.
Laboratory tests were conducted in a two choice wind tunnel in which the
windspeed was maintained constant at 20cm/sec while the room was maintained at 24 ±
1°C and 65 ± 5 % relative humidity. The compounds were dispensed either singly or as a
blend from the dispensers, with 6.028 cm2 diffusion area The weight loss of the
individual compounds was assessed gravimetrically and the release of the individual
compounds in the blend quantitatively determined by gas chromatography (GC). Zero-,
first- and second-order rate models were tested to determine the release kinetics of the
individual compounds and the blend. Comparison of the models using correlation
coefficients (~) indicated that the release of the individual compounds followed fIrstorder
kinetics while the release of the blend followed zero-order kinetics.
In the semifield trials, dispensers were placed either under direct sunlight or under
the shade. Weight loss was assessed gravimetrically and the release of the blend
compounds quantitatively determined by GC. The individual compounds dispensed
singly followed first-order release kinetics while the blend of the compounds followed
zero-order release kinetics. It's however interesting to note that the release of the
individual components of the blend-mixture follows zero-order kinetics under semi-field
conditions contrary to the behaviour exhibited by the individual components dispensed
singly. The repellents placed in dispensers exposed to direct sunlight exhibited higher
rate constants than those in the dispensers placed in the shade. The rate of release was
found to be slightly higher during the first 24 hours and then became steady, obeying
Fick's law of diffusion. The release rates were observed to depend on the surface area of
the tygon tubing and generally increased with temperature. Semifield data was more
variable than laboratory data due to the changing temperature conditions in the field.
Rate constants established under laboratory conditions were slightly lower than
those obtained under semifield conditions. The results indicate that temperature could be
the major environmental determinant of release rates with other variables like relative
humidity having little or no effect. However, the magnitude of the effect of temperature
on the release rates was not easily demonstrated with the field data. It is thus evident that
the release of the compounds was not a simple function of temperature; with the release
rates at higher temperatures being lower than would be expected. The zero-order rate
equation best described the release of the blend, which was found to be diffusioncontrolled.
Controlled release of the blend was therefore achieved using the dispenser. | |
