Wing length and host location in tsetse (Glossina spp.): implications for control using stationary baits

Abstract

BackgroundIt has been suggested that attempts to eradicate populations of tsetse (Glossina spp.) using stationary targets might fail because smaller, less mobile individuals are unlikely to be killed by the targets. If true, tsetse caught in stationary traps should be larger than those from mobile baits, which require less mobility on the part of the flies.ResultsSampling tsetse in the Zambezi Valley of Zimbabwe, we found that the number of tsetse caught from stationary traps, as a percent of total numbers from traps plus a mobile vehicle, was ~5% for male G. morsitans morsitans (mean wing length 5.830 mm; 95% CI: 5.800–5.859 mm) and ~10% for females (6.334 mm; 95% CI: 6.329–6.338 mm); for G. pallidipes the figures were ~50% for males (6.830 mm; 95% CI: 6.821–6.838 mm) and ~75% for females (7.303 mm, 95% CI: 7.302–7.305 mm). As expected, flies of the smaller species (and the smaller sex) were less likely to be captured using stationary, rather than mobile sampling devices. For flies of a given sex and species the situation was more complex. Multivariable analysis showed that, for females of both species, wing lengths changed with ovarian age and the month, year and method of capture. For G. pallidipes, there were statistically significant interactions between ovarian age and capture month, year and method. For G. m. morsitans, there was only a significant interaction between ovarian age and capture month. The effect of capture method was, however, small in absolute terms: for G. pallidipes and G. m. morsitans flies caught on the mobile vehicle had wings only 0.24 and 0.48% shorter, respectively, than flies caught in stationary traps. In summary, wing length in field samples of tsetse varies with ovarian age, capture month and year and, weakly, with capture method. Suggestions that a target-based operation against G. f. fuscipes in Kenya caused a shift towards a smaller, less mobile population of tsetse, unavailable to the targets, failed to account for factors other than capture method.ConclusionsThe results are consistent with the successful use of targets to eradicate populations of tsetse in Zimbabwe. Until further, more nuanced, studies are conducted, it is premature to conclude that targets alone could not, similarly, be used to eradicate G. f. fuscipes populations in Kenya.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3274-x) contains supplementary material, which is available to authorized users.

Improved estimates for extinction probabilities and times to extinction for populations of tsetse (Glossina spp)

“…This is appropriate, however, since the additional mortality due to targets, estimated from mark-recapture data, was also a figure averaged over adult females of all ages. A suggestion of a bias that would favour targets killing larger flies finds no support in the Zimbabwe situation [22, 23].…”

A model for the relationship between wing fray and chronological and ovarian ages in tsetse (Glossinaspp)

“…The collection and analysis techniques were fully described by Hargrove et al . (). Females were classified into one of eight ovarian categories: 0–3 and 4 + 4 n to 7 + 4 n , n = 0, 1, 2, 3 …, where, as explained above, n cannot be identified by ovarian dissection alone.…”

Effects of Human Settlements and Spatial Distribution of Wing Vein Length, Wing Fray Categories and Hunger Stages in Glossina morsitans morsitans (Diptera: Glossinidae) and Glossina pallidipes (Diptera: Glossinidae) in Areas Devoid of Cattle in North-Eastern Zambia

“…In the procedures, 1) levels of wing fray (level of damage to the wings) falls in six (06) categories (i.e., categories 1 to 6)—with category 1 having the least damage and category 6 having the most damage to the wings; 2) hunger stages, based on the appearance of the abdomen, ranging from stage 1 (newly and fully fed tsetse flies) to stage 4 (hungry tsetse flies); and 3) ovarian categories, based on the state of each of the fours ovarioles in relation to release of ova, ranging from ovarian category 0 (newly emerged adult) to category 7 or higher for tsetse flies that are 70 to 80 d old or older—noting that this is the highest category that can be determined in a straight forward manner through the method ( Leak 1999 ). Wing vein length, wing fray categories, and ovarian categories have been applied by several authors, e.g., Allsopp (1985) and Hargrove et al (2019) .…”