Studies on the efficacy of deltamethrin applied to cattle for the control of tsetse flies (Glossina spp.) in southern Africa

Summary The tsetse fly (Glossina spp.) inhabits 11 million km² of Africa (Greekmore, 1989) where it is responsible for the transmission of trypanosomosis to man and animals. Because of its slow rate of reproduction, with females producing only four to five pupae per annum, control of the tsetse fly is the best means of controlling trypanosomosis. A number of different methods have been and are used but, whilst successes have been achieved, a long term solution has not been found.

---

Resumen La mosca tsetsé (Glossina spp.) infesta 11 millones de km² (Greekmore, 1989) donde es responsable de la transmisión de tripanosomiasis al hombre y animales. Debido a la baja tasa de reproducción de la mosca (cuatro a cinco pupas por a?o), el control de la mosca per se es el método más efectivo, habiendose obtenido algún éxito, sin encontrer todavía una solución a largo plazo.

---

Résumé La tsé-tsé (Glossina spp.) occupe 11 millions de km² du sol africain (Greekmore, 1989) et elle est responsable de la transmission de la trypanosomose chez l'homme et les animaux. En raison de son taux lent de reproduction (les femelles ne produisent que 4 à 5 larves par an) la luttre contre la tsétsé est la meilleure méthode pour combattre la trypanosomose. On a utilisé, et on utilise encore, de nombreuses techniques variées et bien que des succès aient été obtenus, aucune solution à long terme n'a encore été trouvée.

     

Recirculation of Trypanosoma brucei brucei in cattle after T. congolense challenge by tsetse flies

The effect of challenging cattle, chronically infected with Trypanosoma brucei brucei, with T. congolense on the development of the T. b. brucei infection was investigated. For this purpose, nine experimental animals were first infected with T. b. brucei through the bites of infected tsetse flies. Once the T. b. brucei had developed into a chronic infection, that was difficult to detect using routine parasitological diagnostic tools, seven of the experimental animals were challenged by tsetse flies infected with T. congolense. Two of the animals infected with T. b. brucei were kept as control. The infection with T. congolense resulted in a sudden increase in the parasitaemia of T. b. brucei. In the T. b. brucei control animals, on the other hand, the parasitaemia remained below the level of detection. The epidemiological repercussions of this increase in the parasitaemia of T. b. brucei after infection with T. congolense are discussed.     

Effect on herd health and productivity of controlling tsetse and trypanosomosis by applying deltamethrin to cattle

Summary A large cattle ranch was established in 1954 in a heavily tsetse infested part of north-east Tanzania. Trypanosomosis was controlled for 30 years by prophylactic drugs but in 1988 drug resistance seemed to be developing as cases of trypanosomosis were being confirmed 4 or 5 weeks after treatment with isometamidium chloride (Samorin). Herd health had deteriorated and productivity was uneconomically low. In order to control the tsetse population the 8,000 cattle, grazing over 250 km², were regularly dipped in the synthetic pyrethroid deltamethrin (Decatix Cattle Dip and Spray formulation). Within a year the tsetse population, as monitored by traps, had decreased by more than 90%. Disease mortality decreased by 66% and a range of productivity measures such as calving percentages and weaning weights were raised to levels above those prevailing before the decline in herd health.

---

Efecto En La Salud Y Productividad Del Hato Al Controlar Tse Tse Y Tripanosomiasis Aplicando Deltamethrin Al Ganado Vacuno

Resumen Un hato grande de ganado fue establecido en 1954 en un area densamente infestada del noreste de Tanzania. Tripanosomiasis fue controlada por 30 anõs usando drogas profilacticas, pero en 1988 resistencia al fármaco pareció desarrollarse ya que casos de tripanosomiasis fueron confirmados 4 o 5 semanas después del tratamiento con isometamidium chloride (Samorin). La salud del hato se habia deteriorado y la productividad era economicamente baja.Para controlar la población de tse tse, las ocho mil cabezas de ganado pastoreando sobre 250 km² fueron regularmente bañados con el pyrethroid deltamethrin sintético (Decatix para inmersion de bovinos y formulacion para aspersion). Dentro de un anõ la población de tse tse, monitoreada a través de trampas, habia disminuído mas del 90%. La mortalidad decrecio cerca de 66% y un rango de medidas de productividad tales como porcentajes de paricion y pesos al destete fueron incrementatdos a niveles arriba de aquellos que prevalecieron antes de la disminucion en la salud del hato.

---

Controle De La Glossines Des Trypanosomoses Par Le Traitement Des Bovins A La Deltamethrine; Effet Sur La Sante Et La Productivite Du Troupeau

Résumé Une grande exploitation pour bovins a été fondée en 1954 dans une region du nord-est de la Tanzanie, hautement infestée par les glossines. Pendant 30 ans la trypanosomose a été controllée a l'aide de drogues prophylactiques mais en 1988 la resistance à ces drogues semble s'être developper car des cas de typanosomose ont été confirmés quatre au cinq semaines après traitement au chloride d'isometamidium (Samorin). L'état sanitaire du troupeau s'est deterioré et la productivité n'etait plus economiquement rentable.Afin de controler la population de glossines, les huit milles de bovins pâturant sur plus de 250 km², ont été régulièrement immergés dans des bains de deltamethrine, pyrethroide de synthèse (Decatix cattle dip et spray formulation). En un an, la population de glossines, evaluée par piégeage a diminuée de plus de 90%. La mortalité due à la maladie a dimunuée de plus de 66% et plusieurs paramètres de productivité, tel que le pourcentage de mise bas et le gain de poids ont atteint des niveaux superieurs a ceux enregistrés avant la degradation de l'état sanitaire du troupeau.

---

---

Reprint requests to: Martin Mitchell, Export Business Group, Pitman-Moore Ltd, Breakspear Road South, Harefield, Uxbridge, Middlesex UB9 6LS, UK.     

Control of tsetse flies and trypanosomes using molecular genetics

TSETSE FLIES (DIPTERA: Glossinidae) are important agricultural and medical vectors transmitting the African trypanosomes, the agents of sleeping sickness disease in humans and various diseases in animals (nagana). While the prevalence of disease has increased to epidemic proportions, lack of a mammalian vaccine and affordable and effective drugs have hindered disease control. Trypanosomiasis management relies heavily on the control of its single insect vector, the tsetse fly. Despite the effectiveness of some of these tools, their impact on disease control has not been sustainable due to their local nature and extensive dependence on community participation. Recent advances in molecular technologies and their application to insects have revolutionized the field of vector biology, and there is hope that such new approaches may form the basis for future tsetse interventions. The success of the genetic approaches aiming to disrupt the transmission cycle of the parasite in their invertebrate host depends on full understanding of the interaction between tsetse and trypanosomes. This article reviews the biology of trypanosome development in the fly and the multiple bacterial symbionts that inhabit the same gut environment. The availability of a genetic transformation system for the midgut symbiont allows for gene products to be expressed in vivo in the tsetse gut where they can produce a hostile environment for pathogen transmission. The characterization of gene product(s) with anti-pathogenic properties and their expression in vivo is discussed. A strategy is outlined where the replacement of susceptible insect phenotypes with their engineered refractory counterparts can result in decreased disease transmission.     

Financial analysis of dipping strategies for indigenous cattle under ranch conditions in Uganda

A financial analysis was performed to assess the performance of three acaricide-treatment groups of indigenous breeds (Zebu and Nganda) of cattle on a ranch in Luwero District, Uganda. The treatments were based on different frequencies: twice-a-week dipping, once-a-month dipping and no tick control. The objective was to evaluate the economic justification for intensive acaricide application for tick and tick-borne disease control in Uganda. Data were collected by monitoring cattle performance over a period of 34 months. Biological data collected included the number of cows at the beginning and end of the study, net starting liveweight, number of calves born, number of animals dying due to tick-borne diseases and other causes, number of animals sold or slaughtered and milk yield. Records of variable costs (acaricides, drugs, labour, etc.) and output prices were assembled and calculated by treatment group. Gross margin and marginal analysis were used in the financial analysis. The exchange rate in 1990–1993 was one US$ to 1200 Uganda shillings. The gross benefits obtained from animal sales, herd value and milk yield were Uganda shillings 1175, 1389 and 1311 per kg of net starting liveweight for animals dipped twice-a-week, once-a-month and not dipped, respectively. The variable costs were Ug. shs. 424, 390 and 360 per kg of net starting liveweight, respectively. Consequently, the gross margins were Ug. shs. 751, 999 and 951 per kg of net starting liveweight. Furthermore, the marginal rate of return (MRR) in changing from no tick control to once-a-month dipping was 160%, while changing from no tick control to twice-a-week dipping was negative (− 313%). The above results showed that the value of increased gains in production obtained from twice-a-week dipping strategy does not offset the costs of inputs for intensive dipping. Once-a-month dipping (strategic) therefore appears to be the most-profitable tick-control strategy for the farmer. The need to conduct further studies in different livestock- production systems and to rationalise future tick control policies is discussed.     

Behaviour of amitraz in cattle dipping baths

The settling rates of 0.025% w/v amitraz (used as a 50% w/w active ingredient wettable powder) and lime stabiliser (0.7% Ca(OH)2) were studied in cattle dipping baths in the Tick Quarantine Area of northern New South Wales. Although lime settled more rapidly than amitraz, the rate for both decreased as the number of cattle dipped increased. After a total of 1,200 head had been dipped the settling rate during the hour following stirring was negligible, and re-stirring was not necessary within the hour following use. Baths could also be cleaned of heavy sediment by scooping without significant loss of chemicals. When the bath volume was allowed to decrease to 2,100 liters below working volume no significant changes in amitraz and Ca(OH)2 concentrations occurred. Data collected from 796 baths showed a significant concentration change of +0.00066% amitraz and -0.017% Ca (OH)2 per 1,000 head of cattle. Replenishment per 700 liters of water with 254 g amitraz was found to be in good agreement with 250 g recommended by the manufacturer, while 12.53 kg for lime was substantially more than the 10 kg recommended.     

New Rickettsia sp. in tsetse flies from Senegal

Tsetse flies are blood-sucking insects transmitting African trypanosomiasis. They are known to harbor also three intracellular bacteria that play important role in their lifecycle: Wigglesworthia glossinidia, Sodalis glossinidius and Wolbachia sp. We have studied 78 Glossina morsitans submorsitans collected in Senegal. In all studied flies we amplified genes of bacterium phylogenetically close to obligate intracellular pathogen Rickettsia felis, the agent of spotted fever in humans. We also visualized this rickettsia in the cells of tsetse flies by fluorescence in situ hybridization. The role of this probable fourth endosymbiotic bacterium of tsetse flies in Glossina lifecycle and possible pathogenecity for humans should be further investigated.     

Maintaining zebu maure cattle in a tsetse infested area of Mali

Summary A study was initiated to evaluate two trypanocidal drugs, the prophylactic isometamidium chloride (Trypamidium) and the curative diminazene aceturate (Berenil) as to their potential for long-term maintenance of zebu cattle in a tsetse infested area of Mali. Trypamidium was administered quarterly and Berenil was administered only as animals were found to be positive for trypanosomes. During the 21-month study trypanosomiasis was the most frequently encountered disease in the cattle in the Berenil treatment group with an average of 5·5 reinfections. The predominant trypanosome species encountered wasTrypanosoma vivax and the most important vector wasGlossina palpalis gambiensis. The results indicate that, even though the direct costs for drugs under the two maintenance regimens were almost identical, the use of Trypamidium resulted in a significantly greater annual weight gain, prevented death loss due to trypanosomiasis and resulted in a herd with a greater market value.

---

Mantenimiento De Ganado Cebu Maure En Una Zona Infestada Por Moscas Tsetse

Resumen Se evaluaron dos drogas contra la tripanosomiasis en Mali. Una profiláctica, Trypamidium, y la otra curativa, Berenil. El Trypamidium (cloruro de isometamidium) se aplicó cada tres meses y el Berenil solo cuando los animales se encontraron positivos. Durante los 21 meses del estudio, tripanosomiasis fue la enfermedad más comunmente encontrada en el grupo tratado con Berenil, con un promedio de reinfección de 5·5. Los tripanosomas predominantes fueron elTrypanosoma vivax y el vector más importante laGlossina palpalis gambiensis. Los resultados del estudio indican que aunque el costo de las drogas para los dos grupos fue casi idéntico, el uso del Trypamidium resultó en un aumento significativo de peso de los animales tratados, previniendo muertes por tripanosomiasis.

---

Maintien De Bovins Zebu Maure Dans Une Region Du Mali Infestee De Glossines

Résumé Une étude fut entreprise pour évaluer deux médicaments trypanocides, le chlorure d'isometamidium (Trypamidium) à titre préventif et l'acéturate de diminazène (Bérénil) à titre curatif, en ce qui concerne leur valeur potentielle pour le maintien à long terme de bovins zébu dans une zone infestée de glossines au Mali. Le Trypamidium était infecté tous les trois mois et le Bérénil seulement lorsque les animaux s'avéraient porteurs de trypanosomes. Pendant les 21 mois de l'étude, la trypanosomose a été la maladie la plus fréquemment rencontrée dans le groupe traité au Bérénil avec en moyenne 5,5 réinfections. L'espèce trypanosomienne prédominante étaitT. vivax et le vecteur le plus importantGlossina palpalis gambiensis. Les résultats montrent que, bien que le coût direct des médicaments dans les deux régimes de maintien ait été presque identique, l'emploi du Trypamidium a engendré un gain de poids annuel significativement plus grand, a prévenu les mortalités dues à la trypanosomose et conduit à un troupeau de valeur marchande plus élevée.

     

A study on the transmission of salivarian trypanosomes isolated from wild tsetse flies

Summary In two distinct areas of East Africa 28,238 and 16,303 non-teneral flies respectively were caught. Infected probosces containing mature trypanosome infections were macerated and inoculated into laboratory animals. Differences in the transmission of trypanosomes existed between different species of tsetse fly. The effect on transmission of trypanosome infection rate in the fly and species of host on which the flies fed is discussed. A method to estimate trypanosome challenge is proposed.

---

Sumario Se atraparon 28,238 y 16,303 moscas tsetse respectivamente en dos areas didtintas de Africa Oriental. Se maceraron proboscis infectadas con tripanosomas maduros y fueron inoculadas en animales de laboratorio. Existieron diferencias en la trasmisión de tripanosomas entre las distintas especies de moscas tsetse. Se discute el efecto obtenido sobre la transmisión por el grado de infección con tripanosomas en la mosca y en hospederos de los cuales la mosca se alimenta.

---

Résumé On a capturé dans deux régions différentes de l'Afrique de l'Est respectivement 28.238 et 16.303 mouches ayant pris au moins un repas. Les trompes infestées, contenant des trypanosomes métacycliques, ont été macérées et inoculées á des animaux de laboratoire. Il existait des différences dans la transmission de trypanosomes entre différentes espéces de glossines. L'effet sur la transmission du taux de l'infection á trypanosomes chez la mouche et l'espèce d'h?te sur lequel les mouches s'étaient nourries est discuté. On propose une méthode pour estimer l'intensité des inoculations trypanosomiennes.

     

AcuteTrypanosoma vivax infection of ethiopian cattle in the apparent absence of tsetse

Summary Investigations of acute trypanosomiasis in a group of 1,200 cattle provided strong evidence for mechanical transmission by haematophagous flies other than tsetse. Although recently introduced cattle may have had previous contact with tsetse flies the incident occurred in an area remote from their known range. Mortality exceeded 6% before the outbreak was controlled by chemotherapy. Mechanically transmittedTrypanosoma vivax infection may be of widespread occurrence in eastern Ethiopia.

---

Infeccion Aguda PorTrypanosoma Vivax En Ganado Etiope En La Ausencia Aparente De Tsetse

Resumen La investigación sobre tripanosomiasis aguda, en un grupo de 1.200 animales, proporcionó evidencia de transmisión por moscas hematófagas diferentes a la tsetse. El incidente ocurrió en un área remota del habitat de la tsetse, aunque un grupo de ganado recientemente introducido, pudo tener algun contacto previo con éstas últimas. La mortalidad excedió el seis por ciento, antes que el brote se controlara. La transmisión puramente mecánica de la tripanosomiasis en Etiopía, podría tener más importancia que la que actualmente se le da.

---

Infection Aigue ATrypanosoma Vivax Chez Les Bovins Ethiopiens Malgre L'Absence Apparente De Tse-Tse

Résumé Les recherches des signes de la Trypanosomiase aiguë conduites dans un groupe de 1200 bovins ont apporté la preuve certaine de la transmission mécanique de la maladie par d'autres insectes hématophages que la tsé-tsé. Bien que du bétail récemment importé ait pu déjà être en contact avec ce vecteur, la maladie est apparue dans une région éloignée de sa zone habituelle. La mortalité a dépassé 6 p. 100 avant que le foyer n'ait pu être contrôlé par la chimiothérapie. La transmission mécanique de l'infection àT. vivax est probablement largement répandue dans l'Est éthiopien.

     

Observations on a heard of beef cattle maintained in a tsetse area

Summary Three groups of Boran cattle were maintained under different trypanocidal drug regimes for 29 months in an area of “medium” tsetse challenge. The development of immunity to trypanosomiasis in the cattle was assessed on the basis of changes in trypanocidal drug requirement, development of parasitaemia, ability to maintain normal blood values, growth and response to challenge after the withdrawal of the drugs. Observations were also made on serum antibody content by immunofluorescence and on serum immunoglobulin levels. Cattle treated with Berenil on the development of clinical disease developed a partial immunity to trypanosomiasis after two years. Cattle treated as a group with Berenil on the development of patent parasitaemia in any one animal of the group did not develop immunity. Cattle treated as a group with Samorin using the same criterion for treatment developed a degree of immunity to the disease. It was concluded that group treatment with Samorin was the most suitable of the three regimes examined for the maintenance of beef cattle in a tsetse infested area.

---

Resumen Se mantuvieron tres grupos de ganado Boran durante 29 meses bajo differentes regímenes terapéuticos en un área donde la concentración de moscas tsetse era mediana. Se llevó a cabo la evaluación del desarrollo de la inmunidad contra la tripanosomiasis teniendo como base los diferentes cambios en el requerimiento de drogas, desarrollo de parasitemia, abilidad para mantener los valores sanguíneos normales, crecimiento y respuestas a la descarga de parásitos después del retiro de la terápia. Se hicieron también observaciones del nivel de anticuerpos séricos por inmunofluorescencia y se determinó el nivel de inmunoglobulinas. Los animales tratados con Berenil cuando mostraban signos clínicos de la enfermedad, desarrollaron una inmunidad parcial a la tripanosomiasis después de dos a?os. Los animales tratados en grupo con Berenil cuando se detectó parasitemia en cualquier animal del grupo no desarrollaron inmunidad. El ganado tratado con Samorin en base de grupo siguiendo el mismo criterio para el tratamiento, desarrolló cierto grado de resistencia a la enfermedad. Se concluye que el tratamiento de grupo utilizando Samorin fue el mejor de los tres regímenes estudiados para el mantenimiento de ganado de carne en un área infestada de moscas tstse.

---

Résumé Trois groupes de bovins Boran ont été maintenus vingt neuf mois, sous différents traitements trypanocides, dans une zone “moyennement” infestée de tsé-tsé. Le développement de l'immunité à la trypanosomiase a été évalué à partir des changements dans les besoins en trypanocides, du développement de la parasitémie, de l'aptitude à maintenir les valuers normales du sang, de la croissance et de la réaction à l'infection après la suppression des médicaments. Des observations ont aussi été faites sur la présence d'anticorps sériques par immunofluorescence et sur les teneurs en immunoglobines sériques. Le bétail traité au Berenil à l'apparition de signes cliniques a été partiellement immunisé au bout de deux ans. Dans le groupe du bétail traité au Berenil à l'apparition d'une parasitémie évidente, aucun animal n'a présenté d'immunité. Le groupe de bovins traité au Samorin, selon les nêmes critères a été bien immunisé.

     

The place of Sanga cattle in dairy production in Uganda

A survey was carried out on milk production and reproductive performance of dairy cattle: 24 farms, with a total of 900 animals and distributed in four agro-ecological zones, were visited every 15 days over 18 months. Cows were fed on natural pastures as the only source of feed, and animal performance was dependent on the season and exhibited a dramatic drop in dry spells. Numeric productivity indices integrating productive performance for settler’s, multipurpose, crop–livestock integrated and modern farms were 0.56, 0.74, 0.69 and 0.63, respectively. Milk productivity was higher on modern farms (6.7 L/cow per day) than in the other systems, and higher with Holstein-Friesian cows (7.7 L/cow per day) than with indigenous cattle (1.8 L/cow per day) or crossbred animals (3.7 L/cow per day). This paper speculates on the opportunity to improve the genetic potential of indigenous cattle, concomitantly with the efforts to adapt exotic cattle to a mountainous equatorial environment.     

Seasonal prevalence of flies feeding on cattle in northern Nigeria

Summary A survey over a year of flies feeding on a tethered bull was carried out on a ranch in the north of Nigeria. Flies were netted on one day in each month for two hours in both morning and afternoon. Flies caught included surface feeders, blood suckers and those causing myiasis. The commonest genus caught wasMusca which was present in relatively large numbers throughout the year.Stomoxys calcitrans was by far the most abundant of the blood-sucking fly species caught.

---

Résumé L'auteur a observé durant toute une année les mouches se nourrissant sur un taureau au piquet, dans un ranch de la Nigéria du Nord. Les captures au filet, ont eu lieu à raison d'un jour par mois et à raison de deux heures le matin, et le soir. Les mouches capturées comprenaient des mouches lécheuses, piqueuses et celles causant des myiases. Le genre le plus communément capturé a été le genreMusca, qui a été de loin le plus abondant parmi les espèces hématophages capturées.

---

Sumario Se efectuó un reconocimiento de un a?o, sobre la prevalencia estacional de moscas, en un rancho localizado en el norte de Nigeria. Las moscas se alimentaron en un toro centinela. La recolección se hizo un día cada mes, dos horas en la ma?ana y dos en la tarde. Se colectaron moscas que sen alimentan en la superficie, moscas hematófogas y las que causan miasis. De todas las capturas, el géneromusca fue el más común y estuvo presente en abundancia todo el a?o. La especie hematófaga más abudante, de todas las atrapadas fue laStomoxys calcitrans.

     

Relationship between ticks and zebu cattle in southern Uganda

Summary Tick populations were observed on zebu(Bos indicus) cattle over a period of 2 years at Entebbe, Uganda where the climate was thought to be highly favourable for the free-living stages of ticks. Collections of all instars of ticks were made from the body surfaces of the cattle at intervals of between 1 and 5 weeks. The species recorded in order of decreasing abundance wereRhipicephalus appendiculatus, Amblyomma variegatum, Boophilus decoloratus, Rhipicephalus evertsi evertsi, Rhipicephalus simus, Rhipicephalus compositus andHyalomma marginatum rufipes. The rankings of the cattle based on burdens of any particular species of tick were always correlated with their rankings for other species; animals that carried more adult stages of a species also carried more of its immature stages. There were more adult males than females ofR. appendiculatus, A. variegatum andR. e. evertsi even when the cattle had had all ticks removed 1 week previously; several possible mechanisms are suggested to explain the biased sex ratio. It is concluded that there is promise for improvement in control of 3-host ticks by increasing the resistance of herds of zebu cattle by culling or selective breeding.

---

Relacion Entre Garrapatas Y Ganado Cebu En El Sur De Uganda

Resumen Se observaron las poblaciones de garrapatas en ganado cebú (Bos indicus) en Entebe, Uganda, donde el clima parecía favorecer a los estados libres de las garrapatas. Las observaciones duraron dos años. Las colecciones de los estadios larvales se realizaron con intervalos de 1 a 5 semanas. Las especies identificadas en orden numérico decreciente fueronRhipicephalus appendiculatus, Amblyommavariegatum, Boophilus decoloratus, Rhipicephalus evertsi evertsi, Rhipicephalus simus, Rhipicephalus compositu andHyalomma marginatum rufipes. Los rangos del ganado basados en la carga de garrapatas de una especie en particular, tuvieron correlación en rangos para otras especies en los animales que tuvieron una carga mayor de etapas maduras de una especie se observaron tambie más ejemplos de las etapas no maduras. Hubo más machos adultos que (hembras deR. appendiculatus, A. variegatum yR. e. evertsi aun cuando todas las garrapatas del ganado habían sido removidas 1 semana previamente; se sugieren varios mecanismos para explicar este fenómeno. Se concluye que existe una posibilidad para controlar garrapatas de 3 huéspedes, incrementando la resistencia de ganado cebú mediante selección y cruzamiento de animales resistentes.

---

Relation Entre Les Tiques Et Les Zebus Dans Le Sud-Est De L'Ouganda

Résumé Des populations de tiques ont été observées sur des zébus (Bos indicus) pendant 2 ans à Entebbe, en Ouganda où le climat est connu pour être très favorable aux stades libres des tiques. Des collections de tous les stades de tiques présentes sur le corps des animaux ont été faites à des intervalles allant de 1 à 5 semaines. Les espèces suivantes ont été recueillies dans l'ordre d'abondance décroissante:Rhipicephalus appendiculatus, Amblyomma variegatum, Boophilus decoloratus, Rhipicephalus evertsi evertsi, Rhipicephalus simus, Rhipicephalus compositus etHyalomma marginatum rufipes. Le classement du bétail basé sur la charge en une espèce de tique a toujours été en corrélation avec la charge dans les autres espèces de tiques. Les animaux porteurs du plus grand nombre d'adultes d'une espèce étaient également porteurs du plus grand nombre de stades préimaginaux. Il y avait beaucoup plus de mâles que de femelles deR. appendiculatus, A. variegatum etR. e. evertsi même lorsqu'on avait prélevé toutes les tiques sur le bétail une semaine auparavant. Plusieurs mécanismes possibles sont suggérés pour expliquer le déséquilibre dans le pourcentage des sexes. La conclusion porte sur les promesses d'amélioration de la lutte contre les tiques trixènes par l'accroissement de la résistance des troupeaux de zébus par élevage sélectif.