Studies on populations of Glossina morsitans morsitans and G. pallidipes (Diptera: Glossinidae) in Rhodesia.
Six methods were used in attempts to estimate the numbers and age structure of populations of Glossina morsitans Westw. and G. pallidipes Aust. in the hot dry season in the Zambesi Valley, Rhodesia. The 13.5-ha study area carried large numbers of both species, and, because the site had abundant shade trees and was surrounded by leafless relatively inhospitable vegetation, the populations were at least partially isolated. Comparable estimates of population size were given by calculations based on the Lincoln Index, inverse sampling, Zippin and probability of capture methods. Error estimates were available only for the inverse sampling approach, and the values for the populations and their associated standard errors were: G. morsitans males 8009 ( plus or minus 1976), G. morsitans females 15 510 ( plus or minus 5359), G. pallidipes males 52 957 ( plus or minus 6295) and G. pallidipes females 167 613 ( plus or minus 19 335). The ratios of non-teneral females to males of both species agree well with those predicted from the population estimates, indicating that, overall, the sampling was not selective. Catches from mobile baits contained high proportions of teneral flies, but most of the tenerals were in fact caught by other trapping methods. Only 1.4% of the estimated teneral flies were caught, and there was no indication of selective capture of either sex of species. A tentative estimate of a total tsetse density of 1.24 flies/m2 was calculated and the estimated average number of puparia per adult fly was 2.3. It was calculated that a minimum of eight buffalo or twenty-five kudu would be required in the study area to support the estimated tsetse population, and analysis of blood-meals indicated that a wide range of hosts was available. The ventilated pit catching method gave good representative catches of females of both species all age-groups. In addition, the mobile ox method also gave good results with G. morsitans, and the resting fly catches can be useful for both species in October. The estimated mean age for female G. morsitans was 29.1 days and for G. pallidipes 48.0 days, with maximum ages of 173 and 226 days, respectively. G. pallidipes females survived better than those of G. morsitans, and there were indications that the highest mortality of both species occurred in young flies. There were no differences in age-structure in catches of males of either species made by a particular catching method. The mean age of male G. morsitans was estimated as 14.7 days, and that of G. pallidipes was about the same. On the basis of calculated ages, the ratio of males to females was 1:3.26 for G. pallidipes and 1:1.98 for G. morsitans. These figures were in good agreement with sex ratios based on the estimated populations.