Evaluation of different blood-feeding frequencies on Glossina palpalis gambiensis performance in a mass-rearing insectary

Background The main challenge to the successful mass-rearing of the tsetse fly in insectaries, especially in Africa, is a sustainable supply of high-quality blood meals. As such, the collection of high-quality blood in large quantities can be an important constraint to production. One possible strategy to lessen the impact of this constraint is to modify the blood-feeding frequency. In the study reported here, we evaluated the effect of three blood-feeding frequencies on the colony performance of Glossina palpalis gambiensis, a riverine tsetse fly species. Methods The effect of three, four and six blood-feedings per week on female survival and productivity were evaluated over a 30-day period. Progeny emergence rate and flight ability were also evaluated. Results Female survival was significantly higher in flies fed four times per week (87%) than in those fed three (72%) and six times per week (78%; P < 0.05). Productivity was similar between flies fed four and six times per week (457 and 454 larvae) but significantly reduced in flies fed three times per week (280 larvae produced; P < 0.05). Both emergence rate and flight ability rate were also similar between flies fed four times per week (97 and 94%, respectively) and six times per week (96 and 97%, respectively), but they were significantly reduced when flies were fed three times per week (89 and 84%, respectively; P < 0.05). Conclusions Blood-feeding frequency could be reduced from six times per week to four times per week without affecting mass-rearing production and progeny quality. The implications of these results on tsetse mass-rearing production are discussed.

Evaluation of different blood feeding frequencies on Glossina palpalis gambiensis performance in a mass-rearing insectary

Background: In tsetse fly mass-rearing insectaries, the sustainable supply of high quality blood meals is the main challenge, especially in Africa. Because the collection of high quality blood in large quantities may be an important constraint to production, blood feeding frequency can be a lever to lessen its impact. Therefore, this study evaluates three blood feeding frequencies on Glossina palpalis gambiensis colony performance.Methods: Three effects of blood feeding treatments - three, four and six times per week - were evaluated on female survival and productivity over a 30-day period. Progeny emergence rate and flight ability were also evaluated.Results: Female survival was significantly higher for flies fed four times per week (87%) than three (72%) and six times (78%; p<0.05). Productivity was similar between flies fed four and six times per week (457 and 454 larvae) but significantly reduced when fed three times (280 larvae produced; p<0.05). Similarly, emergence rate and flight ability rate were both similar between flies fed four times (97% and 94%) and six times (96% and 97%) per week but significantly reduced when fed three times per week (89% and 84%, respectively; p<0.05).Conclusions: Blood feeding frequency could be reduced to four times per week without affecting mass-rearing production and progeny quality. We discuss the implications of these results on tsetse mass-rearing production.

Larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina palpalis gambiensis

Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of trypanosomes, the causative agents of African animal trypanosomosis or nagana in animals and human African trypanosomosis or sleeping sickness in humans. Tsetse flies are K-strategist species with the deposition of a single larva at 10 days intervals in specific sites. As larviposition site selection will strongly impact reproductive success, it is obvious that the selection of larviposition sites is not random and is under strong selective processes, probably mediated by specific cues as suggested by the existence of an aggregation factor in the Morsitans and Fusca groups. This study aimed to highlight the existence of an aggregation effect in the Palpalis group and to test for its chemical nature. We studied the larviposition site selection of Glossina palpalis gambiensis according to the presence of conspecific and heterospecific larvae buried in substrates in different settings. Three sets of experiments were performed with either individual or grouped (n = 50) gravid females, and with physical access to substrate or not. In both individual and grouped larviposition experiments, females selected significantly more often trays conditioned by larvae (P<0.005), either conspecific or heterospecific even in the absence of physical contact with the substrate. These results highlight the first evidence for larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina palpalis gambiensis. However, these compounds seem not to be species-specific and therefore offer new avenues for the behavioural manipulation of these vectors and for the development of new vector control tools targeting gravid females.Author summaryLarviposition site selection in tsetse flies is govern by several biotic and abiotic factors that lead to an aggregation effect of larvae. Among those, larvae are suspected to produce chemicals that drive females to breeding site but little information is available. This study aimed to highlight the existence of an aggregation effect of larval origin in the Palpalis group and to test for its chemical nature. Through behavioural larviposition choice experiments, we showed that females of Glossina palpalis gambiensis deposit their larvae significantly more often in trays conditioned either by conspecific or heterospecific larvae, even in the absence of physical contact with the substrate. These results highlight the first evidence for aggregation effect in Glossina palpalis gambiensis mediated by volatile semiochemicals of larval origin. Isolation and identification of these chemicals should offer new avenues for the behavioural manipulation of these vectors and for the development of new vector control tools targeting gravid females.

Tolerance to a Combination of Low Temperature and Sterilizing Irradiation in Male Glossina palpalis gambiensis (Diptera: Glossinidae): Simulated Transport and Release Conditions

Recently, aerial delivery of sterilized adult tsetse flies has been developed based on the release of chilled adult sterile males. The long-distance transport of irradiated male tsetse pupae for chilled adult release systems requires exposure of the mature pupae to irradiation and to low temperatures for both the pupae and adults. The effect of these treatments on mating of adult Glossina palpalis gambiensis (Vanderplank, Diptera: Glossinidae) males was investigated. Male G. p. gambiensis pupae were stored at 10°C for 5 d and irradiated with 110 Gy within the first 24 h of cold storage. In addition, to simulate a chilled adult release environment, 6-d-old adult males were stored at 5.1 ± 0.4°C for 6 or 30 h. Mating performance was compared to untreated controls in walk-in field cages. A significantly lower proportion of males that had been irradiated and stored at low temperature succeeded in securing a mating compared to untreated males. Premating time, copulation duration and spermathecal fill were similar. Insemination levels were slightly lower for adult males stored at low temperature for 30 h compared to 6 h or control. Although the mating behavior of the males was affected by the treatments given, the data presented confirm the suitability of using long-distance transport of chilled and irradiated male G. p. gambiensis pupae followed by releasing the emerged adult male flies using a chilled adult release system. However, the data indicate that the chilling duration of the adults should be minimized.

Epidémiologie de la trypanosomose animale africaine chez les bovins dans le département du Korhogo (Côte d’Ivoire)

Une étude transversale a été menée dans le département du Korhogo, au nord de la Côte d’Ivoire, dans la zone agropastorale de Katégué, afin de mieux connaître l’épidémiologie de la trypanosomose animale africaine (TAA) chez les bovins. L’étude a associé une enquête entomologique et une enquête parasitologique et s’est déroulée en saison des pluies, de juillet à octobre 2015. Les prospections entomologiques ont été réalisées à l’aide de pièges Vavoua posés dans 30 sites aux biotopes divers. Pour l’enquête parasitologique, 407 bovins ont été prélevés sur la base d’un échantillonnage aléatoire stratifié sans distinction de race, de sexe et d’âge. Les résultats ont montré la présence d’un vecteur majeur de la TAA, la mouche tsé-tsé Glossina palpalis gambiensis, avec une densité apparente globale de 0,9 ± 3,0 glossines par piège par jour. Une seule espèce de trypanosome a été identifiée, Trypanosoma vivax, avec des prévalences relativement faibles aussi bien chez les glossines (11 ± 5 %) que chez les bovins (6 ± 2 %). Compte tenu de la gravité de la TAA chez les bovins, il s’avère nécessaire de sensibiliser les éleveurs du Korhogo, qui représente la principale zone d’élevage de bovins en Côte d’Ivoire, à la lutte contre les vecteurs de la TAA et à l’utilisation rationnelle des trypanocides.