NUTRITIONAL STATES OF MALE TSETSE-FLIES (GLOSSINA SPP) (DIPTERA, GLOSSINIDAE) CAUGHT IN ODOR-BAITED TRAPS AND ARTIFICIAL REFUGES - MODELS FOR FEEDING AND DIGESTION

Male Glossina morsitans morsitans Westwood and Glossina pallidipes Aus ten caught in artificial refuges in Zimbabwe had ca. six times as much haematin and up to 32% more fat than flies from odour-baited traps, b ut haematin-specific fat levels did not differ significantly between m ethods. G. pallidipes estimated to have fed < 9 h prior to sampling co ntained ca. 3.3 mg fat - only 10% less than peak levels. A differentia l equation model for blood-meal metabolism was developed which describ ed well the changes in fat levels of laboratory G. m. morsitans and th e relationship between fat and log haematin in field data. The model p redicts a mean feeding interval (T) of 54 - 65 h and mean fat levels o f ca. 2.8 mg for G. pallidipes at feeding. When haematin frequency dat a were analysed as suggested in the literature, estimates of feeding r ates and intervals, and of the non-feeding phase, varied with sampling method. Published estimates of activitv levels related to feeding sug gest a model where feeding rates increase approximately linearly durin g the trophic cycle. For T 58 h the model gives good predictions of me an fat levels and variances in both species, with starvation rates < 1 % /day. Models with long non-feeding phases predict fat levels up to 40% lower than observed and with smaller variances. For constant feedi ng rates, fat levels were well predicted for T = 54 h, but predicted d eath rates (> 5%/day due to starvation alone) were impossibly high. It is suggested that a proportion of tsetse flies with high fat levels f eed on mobile hosts early in the trophic cycle and that this effect is more marked for G. m. morsitans than for G. pallidipes. Over-estimate s of T result from the failure to consider these tsetse flies and not to errors in the assumed time scale, nor failure to catch high-fat tse tse flies which visit stationary traps.