The use of small plots to study populations of tsetse (Diptera: Glossinidae): Difficulties associated with population dispersal

Abstract

In the Zambezi Valley of Zimbabwe, ULV applications of non-residual insecticide (endosulphan and NRDC 161) were made to a 1.8 x 1.8 km block of woodland infested with Glossina morsitans morsitans Westw. and G. pallidipes Austen. The recapture rates of marked flies released in the centre of the block, and recaptured in odour-baited traps in and around the block, indicated that the insecticides killed about 97% of flies that had been released 1-4 hr before spraying. Catches of unmarked male G. m. morsitans in the centre of the block declined after the insecticide applications, but there was no clear effect on catches of female G. m. morsitans and both sexes of G. pallidipes. Data for the movement of marked flies suggested that the minimum daily rates of movement were about 700 m for male G. m. morsitans and about 800 m for the other tsetse. An increase in dawn temperatures, from 17.5 to 27.5°C, was associated with an increase in the rate movement of G. pallidipes in the early morning. The failure to detect changes in the unmarked populations of female G. m. morsitans and both sexes of G. pallidipes was attributed to the high mobilities of these flies and demonstrated that unmarked populations could not be studied satisfactorily in small plots; studies based on marked populations are recommended for such plots.

Patterns of genetic diversity and differentiation in the tsetse fly Glossina morsitans morsitans Westwood populations in East and southern Africa

“…The high differentiation and corresponding low rates of gene flow are ecologically significant because G. morsitans flies are said to have a great capacity for dispersal (Rogers 1977;Vale et al 1984;Williams et al 1992;Hargrove 2000). Our estimates of gene flow vary from 0.7 to 1.7 reproductive flies per generation, taken over the nine sampled populations.…”

“…Wright's (1978) fixation index (F ST ) averaged across four mtDNA and five microsatellite loci were 0.088 and 0.180, respectively. These differentiation levels were surprising given the well-known vagility of morsitans group flies (Vale et al 1984;Williams et al 1992).…”

Target barriers for tsetse flies (Glossina spp.) (Diptera: Glossinidae): quick estimates of optimal target densities and barrier widths

“…For G. pallidipes females with d 1 km under some circumstances (Vale et al, 1984) and q 0.98 (Vale et al, 1986) the results in figure 2A can be read off directly with the units taken as km. For G. m. morsitans the daily step length may approach 500 m and q 0.99 (Vale et al, 1984(Vale et al, ,1986) so that figure 2A should be read as if the abscissa is marked with target densities 8, 16, ... 128 and the barrier widths marked 0.5,1, 2, 4 km.…”

“…For G. m. morsitans the daily step length may approach 500 m and q 0.99 (Vale et al, 1984(Vale et al, ,1986) so that figure 2A should be read as if the abscissa is marked with target densities 8, 16, ... 128 and the barrier widths marked 0.5,1, 2, 4 km. Thus, for G. m. morsitans a barrier 4 km wide with 16 targets/km 2 gives a probability of penetration of between 0.001 and 0.0001; for approximately the same degree of protection in G. pallidipes a barrier 4 km wide would have to contain targets at 32/km 2 -doubling the total requirement for targets.…”

A dynamic species distribution model of Glossina subgenus Morsitans: The identification of tsetse reservoirs and refugia

“…An individual fly can move up to 800 m per day (Vale et al 1984), while fly populations with a typical 1% growth rate tend to advance much more slowly at ;11.7 km per year or roughly 513m per 16 days in what has been called a ''fly front'' (Hargrove 2000). Since the TED Model is designed to predict tsetse distributions as a whole, the potential movement rate of individual flies is less important.…”