Factors affecting the landing and feeding responses of the tsetse fly Glossina pallidipes to a stationary ox.

In Zimbabwe, studies were made of the landing and feeding responses of Glossina pallidipes on an ox. Of the tsetse approaching an ox, approximately 70% fed. Increasing densities of tsetse increased the grooming responses of the ox but had no significant effect on the percentage of tsetse that engorged. The landing site of tsetse on the ox varied with density, with approximately 50% landing on the legs at low densities (< 20 flies per ox), compared to approximately 80% at densities > 40 flies per ox. For male G. pallidipes, the mean bloodmeal size was 37 mg. The probability of feeding was negatively correlated with fat content, declining from 91% for flies with < 1 mg fat to < 50% for flies with > 4 mg fat. Bloodmeal size was also negatively correlated with fat content; the regression equation relating bloodmeal size and fat content indicated that the mean wet weight declined from 42 mg for flies with 1 mg of fat to 31 mg for flies with 5 mg of fat. For females, the probability of feeding was not significantly affected by age as determined by ovarian category but there was a paucity of young (ovarian category 0) flies attracted to the ox. Pregnancy status had no significant effect on the probability of feeding, but samples of flies attracted to the ox showed a relative dearth of females approaching larviposition and a preponderance just after.