THE IMPLICATIONS OF HUNGER IN THE TSETSE-FLY, GLOSSINA-PALLIDIPES, IN RELATION TO ITS AVAILABILITY TO TRAPPING TECHNIQUES

Mean fat and haematin levels of both sexes of trap-caught Glossina pallidipes were significantly lower than those of flies intercepted approaching the trap or of those departing from the trap without having entered. At the lower end of the haematin range the fat levels of trap caught flies, for specified levels of haematin, were also lower than those of flies in the other two categories. It is suggested that many of the relatively well fed flies that come to a trap would feed opportunistically on a host animal but do not enter the trap. Hence, feeding intervals estimated from trap catches are more likely to represent maximal intervals between feeds than average feeding intervals, because they are based largely on sampling the hungriest portion of the population, Inconsistent relationships were found between fat and haematin values in flies caught by different methods. Wide variations in fat contents for given haematin contents were found and wide variations in haematin contents for given times since feeding have been recorded in field-collected flies of both sexes. For these reasons it is proposed that haematin contents of tsetse cannot be used to estimate reliably the time lapse since the previous blood meal was ingested and that any relationship between fat and haematin content of a tsetse is a poor indicator of rates of fat consumption. The history of feeding success of a fly is better reflected in its fat content alone for a male and its fat content in relation to its pregnancy state for a female.