Comparative gamma-radiation sensitivity of Glossina tachinoides Westv., Glossina fuscipes fuscipes Newst. and Glossina brevipalpis Newst. (Diptera, Glossinidae).

The effect of gamma-radiation doses ranging between 10 and 180 Gy on 4-6-day-old adult males of Glossina tachinoides, Glossina fuscipes fuscipes and Glossina brevipalpis was studied. Fecundity of their mates was reduced by 95% following exposure to 120, 80-100 and 50 Gy of adult male G. tachinoides, G. f. fuscipes and G. brevipalpis respectively. Insemination ability of the males and sperm motility were not adversely affected by the radiation treatment. The higher proportion of dominant lethals in the sperm of the three species with increasing radiation doses was reflected in the reproductive status of the female mates, i.e. an increasing percentage of females showing imbalances between intrauterine content and ovarian development (females with an empty uterus due to expulsion of a dead embryo after embryonic arrest or a degenerating egg in utero) and an acceleration in follicle development associated with successive unsuccessful cycles. In the F1 progeny of all treated groups, no significant bias of the sex ratio was found. The average life span of G. tachinoides and G. f. fuscipes males treated with doses of > or = 80 Gy and of G. brevipalpis males treated with doses >140 Gy was significantly reduced as compared with untreated controls. Male G. brevipalpis treated with doses ranging between 10 and 40 Gy, however, showed a significant radiation induced increase in average life span.

Analysis of the mating scar pattern of Glossina palpalis palpalis (Rob.-Desv.) and Glossina fuscipes fuscipes Newstead (Diptera: Glossinidae).

An analysis was made of the mating scar pattern of female Glossina palpalis palpalis Robineau-Desvoidy and Glossina fuscipes fuscipes Newstead. Measurements on fifty permanent preparations of the mating scars of females reared in the laboratory revealed significant differences in the length, width and in the distance between the centers of the mating scars of the two species. Plotting the distance between the centers of the two mating scars against the ratio width/length resulted in a 93% separation of the two species. It is proposed that this technique could be used during field surveys to expose possible cross-breeding in nature or as a tool in the entomological evaluation of a tsetse eradication campaign where one species is released in the habitat of the other.

The effect of intersubspecific hybridization and gamma radiation on the reproductive biology of Glossina palpalis palpalis (Robineau-Desvoidy) and Glossina palpalis gambiensis Vanderplank.

The closely related tsetse fly subspecies Glossina palpalis palpalis (Nigeria origin) and Glossina palpalis gambiensis (Burkina Faso origin) hybridize readily in the laboratory. Hybridized G.p.palpalis females produced less offspring than the parental intrasubspecific crosses. Adult emergence was below 70% with at least 78% being females. Most female hybrids were fertile whereas most of the male hybrids were sterile when backcrossed to the G.p.palpalis parental line. All F1 males were capable of transferring a spermatophore but their mates rarely had sperm-impregnated spermathecae. Their testes rarely contained mature sperm; moreover, sperm, when present had low or no motility. During laboratory cage tests with virgin females of both subspecies and either sexually mature male G.p.palpalis or G.p.gambiensis, there was no indication for selective mating. The same was true when gamma irradiated males (120 Gy treatment in air) were used. In the latter case complete sterility was induced causing embryonic arrest in all inseminated female mates. Consequently, in ratio tests with untreated virgin G.p.palpalis females, untreated G.p.palpalis males and an increasing number of irradiated G.p.gambiensis males, there was a gradual decrease in production of viable offspring. The results of the present study are discussed with a view of using a combined hybridization and induced sterility in distinct geographical zones where the two subspecies are present.

Effects of gamma irradiation on the midgut ultrastructure of Glossina palpalis subspecies.

In the sterile insect technique, insects are sterilized prior to release in areas where they are pests. The sterile males compete for and with fertile wild individuals for mates, thus reducing the population's reproductive rate. Tsetse fly (Glossina spp.) populations have been eradicated after release of laboratory-bred flies sterilized by gamma irradiation. However, no studies exist on radiation-induced damage to the midgut morphology and function of the radiation-sterilized insects. After G. palpalis palpalis and G. p. gambiensis were subjected to 130 Gy gamma radiation, their midgut damage and recovery were monitored by electron microscopy. The first sign of damage was atrophy and loss of the microvillous border from epithelial cells. The rate of cell degeneration increased, with young as well as old cells being affected and cellular debris filling the ectoperitrophic space. Muscle cells were destroyed, patches of basal lamina were left bare, intracellular virus- and rickettsia-like organisms became more frequent, and many replacement cells became unusually large. Partial recovery occurred from the 10th day postirradiation. Such changes in midgut ultrastructure and the corresponding inhibition of functions may increase the susceptibility of the fly to trypanosome infection.