The effect of humidity and temperature on the extent of abdominal pigmentation inGlossina pallidipesAusten

Abstract

The extent of pigmentation of the abdominal bands ofGlossina pallidipesAust. was studied in specimens emerging in the laboratory from puparia maintained at constant temperature and a range of relative humidities and derived from females collected in the field at Shinyanga, Tanganyika. An index of pigmentation was obtained by regarding the bands as consisting in all of 15 zones, each carrying a score of 1.The index was closely dependent on the humidity experienced during pupal development, almost full pigmentation being produced in saturated air and almost complete suppression of it in dry air; it is inversely related to size and little affected in nearly saturated air by temperatures below 28°C. during pupal development, although still higher temperatures reduce it quite sharply.In flies collected in the field throughout the year, most of those taken towards the end of the rains (March and April) fell into the darker pigment categories; as the dry season advanced the distribution tended to become bimodal, with the darker mode relatively steady at an index of about 12 and the paler mode moving progressively down the scale, reaching an index of about 5 in October and then disappearing. December and January collections (rainy season) were again unimodal, resembling those of March. It is suggested that these changes reflect the use of two types of larviposition site, the darker mode representing pupae from the evergreen thickets along the drainage lines and the lighter mode those from semi-deciduous thickets on the eluvial slopes, and that during the dry season the soil-space humidity in the latter sites may reach levels inimical to survival.The depth to which larvae ofG. pallidipesburrow appears to be related to the temperature, and perhaps the humidity, obtaining at the time of larviposition.The possible effect of humidity on coloration was tested in four other species of tsetse fly, namelyG. swynnertoniAust.,G. morsitansWestw.,G. palpalis fuscipesNewst. andG. longipennisCorti. OnlyG. swynnertonigave indications of some slight effect.