Glossina brevipalpis (Diptera : Glossinidae) in South Africa : distribution, endosymbionts and assessment of irradiated male mating proficiency

Abstract

Glossina brevipalpis found in the north-eastern KwaZulu-Natal Province of South Africa represents the southernmost distributional limit of this genus in Africa. This species covers approximately 18 000 km2 where it co-occurs with its congener G. austeni. An Area Wide-Integrated Pest Management (AW-IPM) strategy that include Sterile Insect Technique (SIT) component was proposed to establish a tsetse free status in South Africa. Initially, this study was designed to only focus on G. brevipalpis however due to the crucial role played by G. austeni in the transmission of trypanosome parasites that cause nagana in South Africa it was included and any control effort needs to consist of both species. This study was aimed at investigating the current apparent density (AD) of the two populations. Subsequently, this study also assessed the male mating ability and the multi mating behavior of the G. brevipalpis. In addition, the detection and abundance of the symbionts (Sodalis and Spiroplasma) harboured by wild captured flies colonized flies as well as to determine the prevalence of trypanosome parasites from wild captured flies. The Apparent Density (AD) of the two tsetse flies were determined using entomological surveys conducted at five protected and four communal farming sites in 2008-2009 and compared to that of 2018-2019. An overall abundance of G. brevipalpis was significantly higher (p < 0.05) with an increase in AD from 4.02 to 5.33 flies /trap/day in 2008-2009 and 2018-2019 respectively. A significant decrease (p > 0.01) in AD from 0.21 in 2008-2009 to 0.14 AD flies/trap/day in 2018-2019 was observed in G. austeni populations from protected areas. These results indicated that the current tsetse control program, as applied in the communal farming areas,

doesn’t have a substantial long-term effect on tsetse abundance and suggest that more efficient control measures be implemented in the affected areas of north-eastern KwaZulu-Natal Province of South Africa. In preparation of the SIT, male mating ability and the female multi mating behavior of G.brevipalpis were determined. For the male mating ability, the flies were given aradiation dose of 80 Gy and allowed to first mate with the 3 days old virgin females followed by second mating with fertile non-irradiated males. Both irradiated and non-irradiated males have shown the potential to mate several times and the propensity of mating as well as the ability to transfer sperm does not decline significantly (p > 0.05) in subsequent mating events. Irradiated males were able to inseminate several females comparable to that on non-irradiated males. The spermatheca fill in females that mated with non-irradiated and irradiated males did not differ. The multi-mating potential of the male tsetse flies from the colony indicated their suitability to be used for SIT based on their mating performance. The multi mating behavior of G. brevipalpis females that first mated with irradiated and then with fertile males was determined under laboratory conditions. As expected, high numbers of pupae were produced by the females that only mated with the fertile males. Females which were only inseminated by irradiated males were going through recurring cycles of aborted eggs. The results showed that younger females appear to be more receptive to a second mating compared to older females. The detection of endosymbionts DNA with species-specific PCR primers were determined. Sodalis were abundant in colonized G. brevipalpis and relatively low in

field collected flies and was not detected in both colonized and field collected G. austeni. Spiroplasma DNA was detected from 37% colonized G. brevipalpis and 30% colonized G. austeni. Trypanosome DNA was detected in 17.4% of field collected tsetse assayed with a high prevalence of Trypanosoma congolense and T. theileri. The initiative to eliminate AAT and tsetse in South Africa need to be supported by accurate information of geographic distribution of tsetse populations as well as information on which Trypanosoma species are prevalent. Such baseline information is crucial when selecting most cost-effective strategy of intervention of the priority areas. This study highlighted that effective control measures are essential in affected areas of north-eastern-KwaZulu-Natal Province. Secondly, this study demonstrated that ARC-OVR tsetse colony flies are suitable to be used in tsetse eradication campaigns in South Africa. Lastly, this study could play a vital role in the decision making on the environmentally friendly tsetse control method that can be implemented in southern Africa.