The Bionomics of Glossina morsitans in the Umniati Fly Belt, Southern Rhodesia, 1922–23

Extract

The pupal period has been shown to be between three and four times as long during the winter months as it is in the summer months.

Breeding continues the whole year round, but the period of greatest density and activity is in September, i.e., towards the end of the dry season. During a period of heavy rains, long grass and full forest foliage, puparia were fairly abundant, while density counts did not indicate any lack of nourishment. The grass in these mopane belts, however, never grows very long.

All types of forest were used for breeding except the heavy river forest. In the mopane a heavy reduction in density occurred after leaf-fall. At the end of the dry season the dry bed of a small well-shaded stream was used extensively as a breeding place. Heavy thorn thickets (Isinanga) and overgrown dongas were only used as breeding places after most of the leaves had fallen.

The puparia are attacked by at least seven species of insect parasites. Of these Mutilla glossinae and possibly two species of Bombyliids are the most important. These parasites show definite seasonal activity. At the end of the dry season, 84 per cent. of all emergences were parasites.

The percentage of collected puparia which failed to yield either flies or parasites increased from 23 per cent. in March to 60 per cent. in November. Experiments showed that half an hour's exposure to the sun (118° F.), even when covered with about one inch of sand, was sufficient to kill the puparia.

The combined effect of parasitism and the hot summer sun on deposited puparia is no doubt a contributary cause of the great fall in density that occurs throughout mopane forest at the end of the late dry season after leaf-fall is complete. This statement does not necessarily apply to other areas not examined.

This fly belt has continued to spread and game has increased, although the area has been thrown open to free shooting since 1905. Between 1924 and 1925 the spread eastward has been rapid, and new settlement areas have been endangered.