Physiological correlates of the availability of Glossina morsitans centralis Machado to different sampling methods

Abstract

Abstract. The feeding cycle for male tsetse flies and the pregnancy cycle for females are used as frameworks for investigating the field behaviour of Glossina morsitans centralis Machado in Zambia, and hence the sampling biases of different capture devices. Flies were collected in the field using hand nets and an electric back pack on foot patrols, and hand nets, hand‐catching and an electric screen on landrover patrols. They were analysed for wing‐fray, vein‐length, chloroform‐extractable fat and haematin. In addition, samples of laboratory‐bred females killed daily during their second pregnancy cycle were analysed for the last two parameters. The daily flying time of males is estimated from the fat—haematin curve to be about 32 min/day, which is identical to previous estimates for G. morsitans from Tanzania. From the varying numbers and fat content of male flies caught by the different sampling methods during the course of the feeding cycle it is concluded that both haematin levels and fat reserves influence fly behaviour. Comparison of the frequency distribution of wild‐caught and laboratory‐bred females along the corrected residual dry weight axis of the pregnancy cycle suggests that the results of combined electric‐trap and hand‐net sampling reflect the actual frequency distribution in the wild population at least for the first 7 days of the pregnancy cycle; but females in the last 2 days of their pregnancy cycle are apparently unavailable to sampling devices, perhaps because of their reduced flight activity. The very variable percentage female catch (10.9–43.4%) returned by the different sampling methods is discussed in the light of the detailed analysis of the differential availability of male and female flies to each capture device.