Glossina fuscipes (Diptera: Hippoboscoidea: Glossinidae)
This week’s insect is Glossina fuscipes, a riverine tsetse fly species found throughout central Africa and as far east as western Kenya. They are common in woodland and forested areas around Lake Victoria. Glossina fuscipes is the principal vector of human trypanosomiasis (Sleeping Sickness) in Uganda and is probably responsible for some few of the infections recorded from the Busia area of western Kenya. Their hosts are predominantly monitor lizards and humans, some of which are also lizards.
Twenty-three species of tsetse flies are known from sub-Saharan Africa, Saudi Arabia and Yemen. All are hematophagous, feeding exclusively on vertebrate blood. A paleontological oddity – while extant Glossina are found nowhere else, four extinct Glossina species were discovered in the Florissant shale of Colorado, USA, dated to 35 million years ago!
We have seven species of tsetse flies in Kenya, Glossina austeni, Glossina brevipalpis Glossina pallidipes, Glossina fuscipes, Glossina fuscipleuris, Glossina longipennis and Glossina swynnertoni. I can’t speak for other species but from personal experience I can say that tsetse flies are very tough critters. At least G. pallidipes is. This species maintains very large populations in southcentral (Nguruman) and southwestern (Lambwe Valley) Kenya. Should you be driving in these areas and have good peripheral vision you can see this species flying alongside your vehicle at speeds of 25 km per hour or so and popping in for a quick meal. This is not a pleasant experience, quite painful in fact. Vengeance quickly becomes the order of the day. Squeezing them between thumb and fore finger will do no good unless you apply significant force. Some say that it is best to simply pull their head off. A grizzly thought. Perhaps better to throw the live fly out, from whence it came, roll up the windows and turn up the AC.
Like humans, and very unlike most other insects, Glossina are K-selected. Animals which have a K-selected reproductive strategy bear a single progeny per reproductive cycle. Adult females feed their larvae to maturity within the mother’s body. Larvae (there are 3 instars) are only minimally exposed to natural enemies because larval development occurs within the pregnant female where they are fed “milk”, a digested product of vertebrate blood. The mature larva is deposited on the soil usually beneath a shrub or other shaded area. The larva digs into the ground and immediately pupates, initiating metamorphosis during which the developing pupa is further protected by the encircling, shed final-instar skin. The whole business is called a puparium. As you can see, the tsetse fly invests considerable resources to produce each offspring. Compare this with that of an insect with the more typical R-selected strategy (e.g. the mosquito). In this case the adult female will lay copious numbers of fertilized eggs per reproductive cycle. She provides no resources to her progeny other than those required for egg development. Her larvae must fend for themselves.
Differing from most other vectors of human disease, tsetse males are also blood feeders (as are males of triatomine bugs, the vectors of Chagas disease in the neotropics). In the other major groups of disease vectors (mosquitoes, sand flies, no-see-ums and black flies) it is only the females that take blood. Males must satisfy themselves with floral nectar.
Even though the female Glossina protects its progeny by retaining all three larval stages in her uterus until she deposits the mature 3rd instar larva on the ground, a number of parasitoid species have been reared from Glossina puparia, including species of the Hymenopteran families Chalcididae, Eulophidae, Diapriidae and Mutillidae and the Dipteran family Bombyliidae. Presumably, these natural enemies can exploit the brief period during which the last instar Glossina larva is exposed. However, infection rates of Glossina by these parasitoids are extremely low and they are of no consequence for tsetse control.
Credits: Dr Robert Copeland