a1 Tsetse and Trypanosomiasis Control Branch, Department of Veterinary Services, Salisbury, Rhodesia
Investigations of the feeding activity, resting behaviour and seasonal distribution of Glossina morsitans Westw. were carried out at Lusulu Veterinary Research Station, Rhodesia, in 1961–63. Nine principal sampling sites were used, one in each of five distinct vegetation types and four at places where various pairs of types met. At each site, from dawn to dusk on several consecutive days in each of four seasons, tsete flies that had engorged naturally on a tethered ox were caught, marked and released, and meterorological readings were taken. Daylight observations of resting flies, both marked and unmarked, were made by searching the vegetation from ground level to a height of 25 feet (with the aid of ladders) and also by placing nets over inaccessible resting places, such as ant-bear holes, at the hottest time of day, thus trapping the flies that emerged later. Attempts to determine the night resting places by releasing flies marked with reflecting paint were unsuccessful.
The results showed that the feeding activity of G. morsitans was restricted to temperatures between 18°C., below which the flies were inactive, and about 32°C., above which they echibited a negative reaction to light. Feeding ceased abrupthy with the onset of darkness, and these was some evidence that activity was reduced by very high light intensity during the middle hours of sunny days. The diurnal pattern of feeding activity varied considerable from season to season but relatively little between vegetation types. A sex ration near equality was observed amongst flies caught feeding on oxen. The proportion of marked flies recaptured (i.e., feeding a second time on a bait-ox) was low, ranging from 0 to 12 per cent. according to vegetation type and season: it was higher for males than for females.
During daylight, the boles and branches of trees were used as resting places in all vegetation types, branches (especially horizontal ones) being preferred at most seasons. When temperatures rose above 32°C., however, the flies removed to resting places in deep shade, e.g., ant-beat holes, rock crevices, tor holes in trees and the fluted boles of dark-barked trees. Searching at night with electric torches failed to reveal the resting places used at that time.
The catches of feeding flies indicated that a wide range of vegetation types at Lusulu were inhabited by G. morsitans at all seasons and that, with the exception of males in riverine vegetation in the hot dry season, vurtually no concentration of flies took place in any specific vegetation at any time of year. These findings are discussed in relation to control by discriminative clearing.
(Received November 12 1965)
* Formerly B. M. Leggate.