CATCHES OF TSETSE (GLOSSINA SPP) (DIPTERA, GLOSSINIDAE) FROM TRAPS AND TARGETS BAITED WITH LARGE DOSES OF NATURAL AND SYNTHETIC HOST ODOR

In Zimbabwe, catches of Glossina morsitans morsitans Westwood and G. p allidipes Austen, at an odour source produced by up to 60 tonnes of ca ttle, fell by 90% from April to October 1987. With the time effect rem oved, the catches were: positively correlated with daily maximum tempe rature; up to twice as high with a trap as with an electrified target; and unaffected by the presence of an incomplete ring of electrified n etting (11.5 m diameter) around the catching site. Catches increased a s a power of bait mass in accord with the theory of odour dispersal. T he power was ca. 0.32-0.44 for G. pallidipes, ca. 0.15 for post-tenera l G. m. morsitans, 0.67 for Stomoxyinae and 0.48 for non-biting muscid s. Earlier results from dose-response studies accord with the new mode l. Tsetse catches were 1.7-4.5 times higher with 20 tonnes of cat-tie as bait than with a synthetic simulate of this dose, consisting of car bon dioxide, acetone, butanone, octenol and phenolic residues. Importa nt 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-tene ral G. pallidipes (45 to 70-80%). Increases in catch for bait mass gre ater than five tonnes were due to increased attraction rather than inc reased efficiency. Targets were 60-66% efficient for G. pallidipes, re gardless of dose; for G. m. morsitans the efficiency was ca. 54% when unbaited and 24-35% when 60 tonnes of cattle were used as bait. The pr obability that G. pallidipes landed on the cloth part of the target, r ather than colliding with the flanking nets, increased as the square o f 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 pr obability for G. m. morsitans and no difference between the sexes; ca. 11% of the catch landed on the cloth portion of the target. Efficienc y and landing behaviour were independent of climate and season.