In Zimbabwe, catches of Glossina morsitans morsitans Westwood and G. pallidipes Austen, at an odour source produced by up to 60 tonnes of cattle, fell by 90% from April to October 1987. With the time effect removed, the catches were: positively correlated with daily maximum temperature; up to twice as high with a trap as with an electrified target; and unaffected by the presence of an incomplete ring of electrified netting (11.5 m diameter) around the catching site. Catches increased as a power of bait mass in accord with the theory of odour dispersal. The power was ca. 0.32–0.44 for G. pallidipes, ca. 0.15 for post-teneral G. m. morsitans, 0.67 for Stomoxyinae and 0.48 for non-biting muscids. Earlier results from dose-response studies accord with the new model. Tsetse catches were 1.7–4.5 times higher with 20 tonnes of cattle as bait than with a synthetic simulate of this dose, consisting of carbon dioxide, acetone, butanone, octenol and phenolic residues. Important olfactory components thus remain to be identified. Trap efficiency for G. m. morsitans rose from 10–20% to 40% with increasing bait mass between 0 and 5 tonnes; thereafter bait mass had no effect. Increased efficiencies were also seen in Stomoxyinae (5 to 60%;) and in post-teneral G. pallidipes (45 to 70–80%). Increases in catch for bait mass greater than five tonnes were due to increased attraction rather than increased efficiency. Targets were 60–66% efficient for G. pallidipes, regardless of dose; for G. m. morsitans the efficiency was ca. 54% when unbajted and 24–35% when 60 tonnes of cattle were used as bait. The probability that G. pallidipes landed on the cloth part of the target, rather than colliding with the flanking nets, increased as the square of the bait mass for both sexes—from 0.11 to 0.22 for males and from 0.06 to 0.15 for females. There was no effect of bait mass on landing probability for G. m. morsitans and no difference between the sexes; ca. 11% of the catch landed on the cloth portion of the target. Efficiency and landing behaviour were independent of climate and season.
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