Radiation dose fractionation and its potential hormetic effects on male Glossina palpalis gambiensis (Diptera: Glossinidae): a comparative study of reproductive and flight quality parameters.

One of the most critical factors for implementing the sterile insect technique for the management of tsetse is the production of large quantities of highly competitive sterile males in the field. Several factors may influence the biological quality of sterile males, but optimizing the irradiation protocols to limit unwanted somatic cell damage could improve male performance. This study evaluated the effect of fractionation of gamma radiation doses on the fertility and flight quality of male Glossina palpalis gambiensis. Induced sterility was assessed by mating irradiated males with virgin fertile females. Flight quality was assessed using a standard protocol. The male flies were irradiated as pupae on day 23-27 post larviposition with 110 Gy, either in a single dose or in fractionations of 10 + 100 Gy and 50 + 60 Gy separated by 1-, 2- and 3-day intervals or 55 + 55 Gy separated by 4-, 8-, and 24-hour intervals. All treatments induced more than 90% sterility in females mated with irradiated males, as compared with untreated males. No significant differences were found in emergence rate or flight propensity between fractionated and single radiation doses, nor between the types of fractionations. Overall, the 50(D0) + 60(D1) Gy dose showed slightly higher induced sterility, flight propensity, and survival of males under feeding regime. Dose fractionation resulted in only small improvements with respect to flight propensity and survival, and this should be traded off with the required increase in labor that dose fractionation entails, especially in larger control programs.

Title: Fractionnement de la dose de rayonnement et ses effets hormétiques potentiels sur les Glossina palpalis gambiensis mâles (Diptera : Glossinidae) : une étude comparative des paramètres de reproduction et de qualité de vol. Abstract: L'un des facteurs les plus critiques pour la mise en œuvre de la technique de l'insecte stérile pour la gestion des glossines est la production de grandes quantités de mâles stériles hautement compétitifs sur le terrain. Plusieurs facteurs peuvent influencer la qualité biologique des mâles stériles, mais l'optimisation des protocoles d'irradiation pour limiter les dommages indésirables aux cellules somatiques pourrait améliorer les performances des mâles. Cette étude a évalué l'effet du fractionnement de la dose d'irradiation gamma sur la fertilité et la qualité de vol des mâles de Glossina palpalis gambiensis. La stérilité induite a été évaluée en accouplant des mâles irradiés avec des femelles vierges et fertiles. La qualité du vol a été évaluée à l'aide d'un protocole standard. Les mouches mâles ont été irradiées sous forme de pupes agées de 23 à 27 jours après la larviposition avec 110 Gy, soit en dose unique, soit en fractions de 10 + 100 Gy et 50 + 60 Gy séparées par 1, 2 et 3 jours ou 55 + 55 Gy séparés par des intervalles de 4, 8 et 24 heures. Tous les traitements ont induit plus de 90 % de stérilité chez les femelles accouplées avec des mâles irradiés par rapport aux mâles non traités. Aucune différence significative n'a été trouvée dans le taux d'émergence ou la propension au vol entre les doses d'irradiation fractionnées et uniques ni entre les types de fractionnements. Dans l'ensemble, la dose de 50 (J0) + 60 (J1) Gy a montré une stérilité induite, une propension à voler et une survie légèrement plus élevées chez les mâles sous régime alimentaire. Le fractionnement de dose n'a entraîné que de légères améliorations en ce qui concerne la propension à voler et la survie, et cela devrait être compensé par l'augmentation nécessaire du travail qu'implique le fractionnement de dose, en particulier dans les programmes de contrôle de grande envergure.

Prevalence of Spiroplasma and interaction with wild Glossina tachinoides microbiota.

Tsetse flies (Diptera: Glossinidae) are vectors of the tropical neglected diseases sleeping sickness in humans and nagana in animals. The elimination of these diseases is linked to control of the vector. The sterile insect technique (SIT) is an environment-friendly method that has been shown to be effective when applied in an area-wide integrated pest management approach. However, as irradiated males conserve their vectorial competence, there is the potential risk of trypanosome transmission with their release in the field. Analyzing the interaction between the tsetse fly and its microbiota, and between different microbiota and the trypanosome, might provide important information to enhance the fly's resistance to trypanosome infection. This study on the prevalence of Spiroplasma in wild populations of seven tsetse species from East, West, Central and Southern Africa showed that Spiroplasma is present only in Glossina fuscipes fuscipes and Glossina tachinoides. In G. tachinoides, a significant deviation from independence in co-infection with Spiroplasma and Trypanosoma spp. was observed. Moreover, Spiroplasma infections seem to significantly reduce the density of the trypanosomes, suggesting that Spiroplasma might enhance tsetse fly's refractoriness to the trypanosome infections. This finding might be useful to reduce risks associated with the release of sterile males during SIT implementation in trypanosome endemic areas.

Title: Prévalence de Spiroplasma et interaction avec le microbiote des Glossina tachinoides sauvages. Abstract: Les mouches tsé-tsé (Diptera : Glossinidae) sont les vecteurs de maladies tropicales négligées, la maladie du sommeil chez l'homme et la nagana chez les animaux. L'élimination de ces maladies est liée à la lutte contre le vecteur. La technique de l'insecte stérile (TIS) est une méthode respectueuse de l'environnement qui s'est révélée efficace lorsqu'elle est appliquée dans le cadre d'une approche de lutte antiparasitaire intégrée à l'échelle d'une zone. Cependant, comme les mâles irradiés conservent leur compétence vectorielle, il existe un risque potentiel de transmission des trypanosomes lors de la libération des mâles sur le terrain. L'analyse de l'interaction entre la mouche tsé-tsé et son microbiote, et entre différents microbiotes et le trypanosome, pourrait fournir des informations importantes pour améliorer la résistance de la mouche à l'infection trypanosomienne. Cette étude sur la prévalence de Spiroplasma dans les populations sauvages de sept espèces de glossines d'Afrique de l'Est, de l'Ouest, centrale et australe a montré que Spiroplasma est présent uniquement chez Glossina fuscipes fuscipes et Glossina tachinoides. Chez G. tachinoides, un écart significatif par rapport à l'indépendance dans la co-infection par Spiroplasma et Trypanosoma spp. a été observé. De plus, les infections à Spiroplasma semblent réduire considérablement la densité des trypanosomes, ce qui suggère que Spiroplasma pourrait renforcer le caractère réfractaire de la mouche tsé-tsé aux infections trypanosomiennes. Cette découverte pourrait être utile pour réduire le risque associé à la libération de mâles stériles lors de la mise en œuvre de la TIS dans les zones d'endémie trypanosomienne.

X-rays are as effective as gamma-rays for the sterilization of Glossina palpalis gambiensis Vanderplank, 1911 (Diptera: Glossinidae) for use in the sterile insect technique.

An area-wide integrated pest management strategy with a sterile insect technique (SIT) component requires a radiation source for the sterilisation of male insects. Self-contained gamma irradiators, which were exclusively used in past SIT programmes, are now facing increasing constraints and challenges due to stringent regulations. As a potential alternative, new generation high output X-ray irradiators have been proposed. The feasibility of using X-ray irradiators was assessed by comparing the effects of both gamma- and X-ray irradiators on biological parameters of Glossina palpalis gambiensis (Vanderplank, 1911), that are important for SIT applications. The gamma irradiator Foss Model 812 and two X-ray irradiators, the Rad Source 2400 and the blood irradiator Raycell Mk2 were used. Glossina palpalis gambiensis males were exposed to radiation as pupae. A radiation dose of 110 Gy or above induced more than 97% sterility in females that mated with the irradiated males for all the irradiators. Adult emergence rate, flight propensity, survival and mating performance did not differ between gamma- and X-rays irradiators. These results suggest that irradiating pupae with a dose of 110 Gy is optimal for both gamma-and X-ray irradiators used in this study, to achieve a sterility of approximately 99%. Similar research on other tsetse species could gradually phase out the use of gamma-ray irradiators in favour of X-rays irradiators, especially for smaller SIT programmes.

Near-infrared imaging for automated tsetse pupae sex sorting in support of the sterile insect technique.

Tsetse flies are the cyclical vectors of African trypanosomes and one of several methods to manage this vector is the sterile insect technique (SIT). The ability to determine the sex of tsetse pupae with the objective to separate the sexes before adult emergence has been a major goal for decades for tsetse management programmes with an SIT component. Tsetse females develop faster and pharate females inside the pupae melanise 1-2 days before males. This earlier melanisation can be detected by infrared cameras through the pupal shell, and the newly developed Near InfraRed Pupae Sex Sorter (NIRPSS) takes advantage of this. The melanisation process is not homogeneous for all fly organs and the pupa needs to be examined ventrally, dorsally and laterally to ensure accurate classification by an image analysis algorithm. When the pupae are maturing at a constant temperature of 24 °C and sorted at the appropriate age, 24 days post-larviposition for Glossina palpalis gambiensis, the sorting machine can efficiently separate the sexes. The recovered male pupae can then be sterilised for field releases of males, while the rest of the pupae can be used to maintain the laboratory colony. The sorting process with the new NIRPSS had no negative impact on adult emergence and flight ability. A mean male recovery of 62.82 ± 3.61% was enough to provide sterile males to an operational SIT programme, while mean contamination with females (4.69 ± 3.02%) was low enough to have no impact on the maintenance of a laboratory colony.

Title: Imagerie dans l'infrarouge proche pour le tri automatisé du sexe des pupes de glossines comme aide à la technique de l'insecte stérile. Abstract: Les glossines sont les vecteurs cycliques des trypanosomes africains et la technique de l'insecte stérile (TIS) est l'une des méthodes de gestion de ce vecteur. La capacité à déterminer le sexe des pupes de glossines dans le but de séparer les sexes avant l'émergence des adultes a été un objectif majeur, pendant des décennies, pour les programmes de lutte contre les glossines avec une composante TIS. Les femelles tsé-tsé se développent plus rapidement et les pharates femelles à l'intérieur des pupes se mélanisent 1 à 2 jours avant les mâles. Cette mélanisation précoce peut être détectée par des caméras infrarouges à travers la coque de la pupe, ce que le nouveau trieur de sexe des pupes dans le proche infrarouge (TSPPIR) utilise. Le processus de mélanisation n'est pas homogène pour tous les organes de la mouche et la pupe doit être examinée ventralement, dorsalement et latéralement pour assurer une classification précise par un algorithme d'analyse d'image. Lorsque les pupes mûrissent à une température constante de 24 °C et sont triées à l'âge approprié, 24 jours après la larviposition pour Glossina palpalis gambiensis, la machine de tri peut séparer efficacement les sexes. Les pupes mâles récupérées peuvent ensuite être stérilisées pour les lâchers de mâles sur le terrain tandis que le reste des pupes peut être utilisé pour maintenir la colonie de laboratoire. Le processus de tri avec le nouveau TSPPIR n'a eu aucun impact négatif sur l'émergence et la capacité de vol des adultes. Une récupération moyenne des mâles de 62,82 ± 3,61% était suffisante pour fournir des mâles stériles à un programme TIS opérationnel, tandis que la contamination moyenne par les femelles (4,69 ± 3,02%) était suffisamment faible pour n'avoir aucun impact sur le maintien d'une colonie de laboratoire.

Prevalence of Trypanosoma and Sodalis in wild populations of tsetse flies and their impact on sterile insect technique programmes for tsetse eradication.

The sterile insect technique (SIT) is an environment friendly and sustainable method to manage insect pests of economic importance through successive releases of sterile irradiated males of the targeted species to a defined area. A mating of a sterile male with a virgin wild female will result in no offspring, and ultimately lead to the suppression or eradication of the targeted population. Tsetse flies, vectors of African Trypanosoma, have a highly regulated and defined microbial fauna composed of three bacterial symbionts that may have a role to play in the establishment of Trypanosoma infections in the flies and hence, may influence the vectorial competence of the released sterile males. Sodalis bacteria seem to interact with Trypanosoma infection in tsetse flies. Field-caught tsetse flies of ten different taxa and from 15 countries were screened using PCR to detect the presence of Sodalis and Trypanosoma species and analyse their interaction. The results indicate that the prevalence of Sodalis and Trypanosoma varied with country and tsetse species. Trypanosome prevalence was higher in east, central and southern African countries than in west African countries. Tsetse fly infection rates with Trypanosoma vivax and T. brucei sspp were higher in west African countries, whereas tsetse infection with T. congolense and T. simiae, T. simiae (tsavo) and T. godfreyi were higher in east, central and south African countries. Sodalis prevalence was high in Glossina morsitans morsitans and G. pallidipes but absent in G. tachinoides. Double and triple infections with Trypanosoma taxa and coinfection of Sodalis and Trypanosoma were rarely observed but it occurs in some taxa and locations. A significant Chi square value (< 0.05) seems to suggest that Sodalis and Trypanosoma infection correlate in G. palpalis gambiensis, G. pallidipes and G. medicorum. Trypanosoma infection seemed significantly associated with an increased density of Sodalis in wild G. m. morsitans and G. pallidipes flies, however, there was no significant impact of Sodalis infection on trypanosome density.

A distribution model for Glossina brevipalpis and Glossina austeni in Southern Mozambique, Eswatini and South Africa for enhanced area-wide integrated pest management approaches.

BACKGROUND: Glossina austeni and Glossina brevipalpis (Diptera: Glossinidae) are the sole cyclical vectors of African trypanosomes in South Africa, Eswatini and southern Mozambique. These populations represent the southernmost distribution of tsetse flies on the African continent. Accurate knowledge of infested areas is a prerequisite to develop and implement efficient and cost-effective control strategies, and distribution models may reduce large-scale, extensive entomological surveys that are time consuming and expensive. The objective was to develop a MaxEnt species distribution model and habitat suitability maps for the southern tsetse belt of South Africa, Eswatini and southern Mozambique. METHODOLOGY/PRINCIPAL FINDINGS: The present study used existing entomological survey data of G. austeni and G. brevipalpis to develop a MaxEnt species distribution model and habitat suitability maps. Distribution models and a checkerboard analysis indicated an overlapping presence of the two species and the most suitable habitat for both species were protected areas and the coastal strip in KwaZulu-Natal Province, South Africa and Maputo Province, Mozambique. The predicted presence extents, to a small degree, into communal farming areas adjacent to the protected areas and coastline, especially in the Matutuíne District of Mozambique. The quality of the MaxEnt model was assessed using an independent data set and indicated good performance with high predictive power (AUC > 0.80 for both species). CONCLUSIONS/SIGNIFICANCE: The models indicated that cattle density, land surface temperature and protected areas, in relation with vegetation are the main factors contributing to the distribution of the two tsetse species in the area. Changes in the climate, agricultural practices and land-use have had a significant and rapid impact on tsetse abundance in the area. The model predicted low habitat suitability in the Gaza and Inhambane Provinces of Mozambique, i.e., the area north of the Matutuíne District. This might indicate that the southern tsetse population is isolated from the main tsetse belt in the north of Mozambique. The updated distribution models will be useful for planning tsetse and trypanosomosis interventions in the area.

Gamma Irradiation and Male Glossina austeni Mating Performance.

An area-wide integrated pest management (AW-IPM) strategy with a sterile insect technique (SIT) component has been proposed for the management of African animal trypanosomosis (AAT) in South Africa. In preparation for the SIT, the mating performance of colony reared Glossina austeni males under influencing factors such as radiation dose and the development stage that is exposed to radiation, was assessed under laboratory and semi-field conditions. The radiation sensitivity of G. austeni colonized 37 years ago when treated as adults and late-stage pupae was determined. Radiation doses of 80 Gy and 100 Gy induced 97-99% sterility in colony females that mated with colony males treated as adults or pupae. Males irradiated either as adults or pupae with a radiation dose of 100 Gy showed similar insemination ability and survival as untreated males. Walk-in field cage assessments indicated that a dose of up to 100 Gy did not adversely affect the mating performance of males irradiated as adults or late stage pupae. Males irradiated as adults formed mating pairs faster than fertile males and males irradiated as pupae. The mating performance studies indicated that the colonized G. austeni males irradiated as adults or late stage pupae will still be suited for SIT.

Using genetic and phenetic markers to assess population isolation within the southernmost tsetse fly belt in Africa.

The effective control of tsetse flies (Diptera; Glossinidae), the biological vectors of trypanosome parasites that cause human African trypanosomosis and African animal trypanosomosis throughout sub-Saharan Africa, is crucial for the development of productive livestock systems. The degree of genetic isolation of the targeted populations, which indicate reinvasion potential from uncontrolled areas, will be critical to establish a control strategy. Molecular and morphometrics markers were used to assess the degree of genetic isolation between seemingly fragmented populations of Glossina brevipalpis Newstead and Glossina austeni Newstead present in South Africa. These populations were also compared with flies from adjacent areas in Mozambique and Eswatini. For the molecular markers, deoxyribonucleic acid was extracted, a r16S2 Polymerase chain reaction (PCR) was performed and the PCR product sequenced. Nine landmarks were used for the morphometrics study as defined by vein intersections in the right wings of female flies. Generalised Procrustes analyses and regression on centroid size were used to determine the Cartesian coordinates for comparison between populations. Both methods indicated an absence of significant barriers to gene flow between the G. brevipalpis and G. austeni populations of South Africa and southern Mozambique. Sustainable control can only be achieved if implemented following an area-wide management approach against the entire G. brevipalpis and G. austeni populations of South Africa and southern Mozambique. Limited gene flow detected between the G. austeni population from Eswatini and that of South Africa or Mozambique may imply that these two populations are in the proses of becoming isolated.

The influence of temperature and humidity on the flight activity of Culicoides imicola both under laboratory and field conditions.

BACKGROUND: Insight into the factors that regulate the circadian host-seeking flight activity of Culicoides vectors (Diptera: Ceratopogonidae) will be of importance to assess the risk of transmission of Culicoides-borne pathogens. This study aimed to determine the impact of temperature and humidity on the flight activity of Culicoides imicola Kieffer, and other livestock associated Culicoides species, under both laboratory and field conditions. METHODS: Batches of 500 field-collected C. imicola females were acclimatized at a predetermined range of temperatures (10-29 °C) and relative humidity (34-85%). After acclimatization, these females, prompted by a light source, were allowed to escape through a transparent plastic funnel into a paper cup, where they were counted after an hour. Flight activity under field conditions was determined seasonally by hourly light trap collections done overnight at four sites near cattle. RESULTS: Experiments conducted at various test conditions in the laboratory indicated that flight activity started at 13 °C. Peak in activity was observed between 16 °C to 18 °C, and temperatures above 20 °C seemingly inhibit flight. Under field conditions, a peak in numbers collected was observed immediately after sunset. With mean nocturnal temperatures below 19 °C, more than 74% of the Culicoides were collected within two to three hours after sunset. With mean nocturnal temperature above 19 °C, the peak in numbers at sunset was sustained until after midnight, with somewhat higher numbers collected after midnight once temperatures dropped below 20 °C. No peak in numbers was observed at dawn. Although very low numbers were collected during the day, which partly may have been a result of the collecting method, Culicoides were present throughout periods of 24 hours. Humidity seemed to play a minor role in the regulation of flight activity. CONCLUSIONS: Abundance and species diversity results as obtained in this study indicated a high level of risk of virus transmission in the first hours following sunset. A strong relationship was found between host-seeking activity, and hence trap efficiency, and within limits, temperature. Light traps primarily measure flight activity and may as such underestimate adult abundance of C. imicola if deployed at temperatures outside thresholds of 16-20 °C.

Evaluation of radiation sensitivity and mating performance of Glossina brevipalpis males.

BACKGROUND: Area-wide integrated pest management strategies that include a sterile insect technique component have been successfully used to eradicate tsetse fly populations in the past. To ensure the success of the sterile insect technique, the released males must be adequately sterile and be able to compete with their native counterparts in the wild. METHODOLOGY/PRINCIPAL FINDINGS: In the present study the radiation sensitivity of colonised Glossina brevipalpis Newstead (Diptera; Glossinidae) males, treated either as adults or pupae, was assessed. The mating performance of the irradiated G. brevipalpis males was assessed in walk-in field cages. Glossina brevipalpis adults and pupae were highly sensitive to irradiation, and a dose of 40 Gy and 80 Gy induced 93% and 99% sterility respectively in untreated females that mated with males irradiated as adults. When 37 to 41 day old pupae were exposed to a dose of 40 Gy, more than 97% sterility was induced in untreated females that mated with males derived from irradiated pupae. Males treated as adults with a dose up to 80 Gy were able to compete successfully with untreated fertile males for untreated females in walk-in field cages. CONCLUSIONS/SIGNIFICANCE: The data emanating from this field cage study indicates that, sterile male flies derived from the colony of G. brevipalpis maintained at the Agricultural Research Council-Onderstepoort Veterinary Institute in South Africa are potential good candidates for a campaign that includes a sterile insect technique component. This would need to be confirmed by open field studies.

Improving the Diet for the Rearing of Glossina brevipalpis Newstead and Glossina austeni Newstead: Blood Source and Collection - Processing - Feeding Procedures.

One of the challenges to maintain tsetse fly (Diptera: Glossinidae) colonies is the sustainable supply of high quality blood meals. The effect of using anticoagulants during collection of the blood, the addition of phagostimulants to the blood meals as well as using mixtures of bovine and porcine blood in different proportions for feeding on colony productivity was assessed. Defibrinated bovine blood was found to be suitable to maintain both the Glossina brevipalpis Newstead and Glossina austeni Newstead colonies. Blood collected with the anticoagulants sodium citrate, citric sodium combination, citrate phosphate dextrose adenine and citric acid did not affect colony performance of both species. Defibrinated bovine and porcine blood in a 1:1 ratio or the feeding of either bovine or porcine blood on alternating days improved pupae production of G. austeni and can be used to enhance colony growth. Bovine blood is appropriate to maintain G. brevipalpis colonies, however, feeding either bovine or porcine blood on alternating days did improve productivity. Adding the phagostimulants inosine tri-phosphate, cytosine mono-phosphate and guanosine mono-phosphate to the blood at a concentration of 10-4 M improved pupae production of the G. brevipalpis colony. The addition of adenosine tri-phosphate and inosine tri-phosphate improved the performance of the G. austeni colony. Decisions on the most suitable rearing diet and feeding protocols will not only depend on the biological requirements of the species but also on the continuous supply of a suitable blood source that can be collected and processed in a cost-effective way.

An update of the tsetse fly (Diptera: Glossinidae) distribution and African animal trypanosomosis prevalence in north-eastern KwaZulu-Natal, South Africa.

An unpredicted outbreak of African animal trypanosomosis or nagana in 1990 in north-eastern KwaZulu-Natal necessitated an emergency control programme, utilising the extensive cattledipping system in the area, as well as a reassessment of the tsetse and trypanosomosis problem in the province. Since 1990, sporadic blood sampling of cattle at the dip tanks in the naganainfested areas were undertaken to identify trypanosome species involved and to determine the infection prevalence in cattle. The distribution and species composition of the tsetse populations in the area were also investigated. From November 2005 to November 2007 selected dip tanks were surveyed for trypanosome infection prevalence. During April 2005 to August 2009 the distribution and abundance of tsetse populations were assessed with odour-baited H traps. The tsetse and trypanosome distribution maps were updated and potential correlations between tsetse apparent densities (ADs) and the prevalence of trypanosomosis were assessed. Glossina brevipalpis Newstead and Glossina austeni Newstead were recorded in locations where they have not previously been collected. No significant correlation between tsetse relative abundance and nagana prevalence was found, which indicated complex interactions between tsetse fly presence and disease prevalence. This was epitomised by data that indicated that despite large differences in the ADs of G. austeni and G. brevipalpis, trypanosome infection prevalence was similar in all three districts in the area. This study clearly indicated that both tsetse species play significant roles in trypanosome transmission and that it will be essential that any control strategy, which aims at sustainable management of the disease, should target both species.

Determination of the optimal mating age of colonised Glossina brevipalpis and Glossina austeni using walk-in field cages in South Africa.

BACKGROUND: For the control of Glossina brevipalpis and Glossina austeni that occur in South Africa an area-wide integrated pest management (AW-IPM) program with a sterile insect technique (SIT) component has been proposed. The quality of the released sterile male tsetse flies will greatly determine the success of the SIT component of the programme. Sterile males need to be able to compete with wild males immediately after their release in the affected area. The mating competitiveness can be affected by many factors including the optimal mating age of the fly which can have an impact on the timing of the release. METHODS: To assess the optimal mating age for G. brevipalpis and G. austeni, mating competitiveness studies were carried out in a walk-in field cage. First, the time of peak fly activity was determined by performing the experiment in the morning and then again in the afternoon. Thereafter, 3, 6 and 9-day-old male flies competed for 3-day-old virgin females. RESULTS: There were no significant differences in mating performance when the field cage experiments were done in the morning or in the afternoon. However, the mating latency was shorter in the afternoon than in the morning. For both species 9-day-old males mated significantly more often than 6 or 3-day-old males. Age did not affect the males' ability to transfer sperm, mating duration or the mating latency. All females that mated were inseminated. CONCLUSIONS: Age did influence the mating competitiveness of G. brevipalpis and G. austeni and it is recommended that sterile males are not released before the age of 9 days. Keeping the male flies in the rearing facility for 8 days will have economic and logistic consequences for AW-IPM programmes that have a SIT component.

Survey of blackfly (Diptera: Simuliidae) annoyance levels and abundance along the Vaal and Orange Rivers, South Africa.

Blackflies (Diptera: Simuliidae) are pests in the livestock and labour-intensive farming systems along the major rivers in South Africa. Since 1995, blackflies have been controlled in the Orange River with the larvicide Bacillus thuringienses var. israelensis (Bti). During 2006-2007, the views of livestock farmers concerning blackfly annoyance were determined by means of questionnaires. The results of the questionnaires were substantiated by seasonal abundance surveys of the sub-adult stages of blackflies, conducted in 2007 at 13 sites in the Orange River and 11 sites in the Vaal River. More than half (52%) of the 39 participating farmers along the Orange River and 79% of the 52 participating farmers along the Vaal River stated that they experienced severe blackfly problems. The majority of farmers were unaware of the availability of products that could be used to protect their animals against blackfly attacks and were willing to be involved in blackfly research. High numbers of blackfly sub-adult stages found in both rivers supported the high annoyance levels reported by the respondents. Simulium chutteri, Simulium damnosum s.l., Simulium hargreavesi, Simulium adersi and Simulium alcocki were identified at Christiana and Delportshoop on the Vaal River, whilst S. chutteri, S. damnosum s.l., S. adersi, S. alcocki and Simulium gariepense were identified at Marksdrift and Ses Bridge on the Orange River. Despite the extensive control of blackflies, farmers still experience problems and this contention is supported by surveys conducted along the rivers.