Mating behaviour and competitiveness of male Glossina brevipalpis and Glossina austeni in relation to biological and operational attributes for use in the Sterile Insect Technique

[摘要] English: In South Africa, African Animal Trypanosomosis (AAT), caused by Trypanosomae parasites transmitted by Glossina brevipalpis and Glossina austeni (Diptera: Glossinidae), is restricted to the north east of KwaZulu-Natal Province with an estimated 250 000 cattle being at risk. For the control of these flies an area-wide integrated pest management (AW-IPM) strategy with a sterile insect technique (SIT) component has been proposed.Accurate knowledge of the distribution of target populations is fundamental to the success of any control programme. In the present study tsetse fly distribution was determined with odour baited H traps and cattle screened using the buffy coat analyses to produce updated tsetse fly distribution, abundance and trypanosome prevalence maps for north eastern KwaZulu-Natal. Glossina brevipalpis and G. austeni were collected in areas where they had previously not been captured. Vegetation and temperature was shown to influence their distribution and abundance. The fact that no significant correlation between tsetse fly abundance and nagana prevalence could be established underlines the complex interactions between these two entities. This was epitomised by the fact that despite large differences in the apparent densities of G. austeni and G. brevipalpis, overall trypanosome prevalence was similar in all districts in north eastern KwaZulu-Natal. This indicated that both species can play a role in transmission of AAT and need to be controlled.The G. brevipalpis and G. austeni populations of north eastern KwaZulu-Natal extends into southern Mozambique (both species) and Swaziland (G. austeni). Morphometrical analyses showed an absence of any significant barriers to gene flow between the various KwaZulu-Natal populations as well as between the South African populations and those of the two neighbouring countries. Tsetse fly control in a localised area will therefore be subjected to reinvasion from uncontrolled areas. An area-wide approach, i.e. against the entire tsetse fly population of South Africa, southern Mozambique and Swaziland will therefore be essential.The maintenance of colonised G. brevipalpis and G. austeni at the Agricultural Research Council-Onderstepoort Veterinary Institute (ARC-OVI), necessitate a high quality blood source. For the potential improvement of the current rearing diet various anticoagulants, phagostimulants and blood sources were evaluated and production assessed using standardised 30-day bioassays. Defibrinated bovine blood was found to be the most suitable. Anticoagulants such as sodium citrate, a combination of citrate and sodium acid, phosphate dextrose adenine and citric acid can be used to simplify blood collection. While G. brevipalpis preferred bovine to porcine blood, G. austeni preferred a mixture of equal parts bovine and porcine blood. The phagostimulants adenosine triphosphate, as well as tri-posphates of inosine, and the mono-posphates of guanosine and cytosine improved production in both species. Attempts to colonise the local KwaZulu-Natal strain of G. brevipalpis failed due to a reluctance of field flies to feed on the artificial feeding system.In preparation for the SIT component the irradiation sensitivity of colonised G. brevipalpis and G. austeni when treated as adults and late-stage pupa was determined. A dose of 40 Gy induced 97% sterility in G. brevipalpis males when irradiated as late-stage pupae and 80 Gy induced a 99% sterility in flies irradiated as adults. Higher doses were required for G. austeni, with 80 Gy and 100 Gy inducing higher than 97% sterility in females that mated with males treated as adults or late-stage pupae.As colonised and irradiated males must be able to compete with their wild counterparts the mating performance of the colonised G. brevipalpis and G. austeni was determined under near natural conditions in walk-in field cages. Although the mating latency for both species was shorter, their mating performance did not differ significantly between mornings and afternoons. For both species mating frequency was significantly higher in nine-day-old males compared to six- or three-day-old males. Age did not affect the males' ability to transfer sperm, their mating duration or mating latency. There was no significant difference in mating performance of sterile and fertile males.This study indicated that AAT and tsetse flies are abundant in KwaZulu-Natal and tsetse fly presence seems to be a dynamic process that is influenced by a number of environmental factors. The earlier proposed AW-IPM strategy with a SIT component, although still applicable, will need to be adapted to incorporate the new distributions records. Initial results indicate that the colonies at the ARC-OVI will be suitable for programmes that have a SIT component.

[发布机构] University of the Free State