Issaka Youssao Abdou Karim

Evidence of multiple mechanisms of alphacypermethrin and deltamethrin resistance in ticks Rhipicephalus microplus in Benin, West Africa

Ticks are obligate haematophagous arthropods, causing heavy losses in affected livestock. The objective of this study is to investigate phenotypic and genotypic resistance in Rhipicephalus microplus populations from Benin. Engorged female adult ticks were collected from cattle in two districts of Benin. Bioassays, biochemical and molecular tests were carried out on these ticks to determine the phenotypic, enzymatic and genetic status of resistance. Results of bioassays showed high resistance factors (RF > 41). The molecular tests showing the presence of the domain II mutation and absence of the domain III mutation in the voltage-gated sodium channel gene. Biochemical tests showed increased activity of esterases, multifunction oxidases and glutathione transferases in resistant samples. Genotyping the samples showed high levels of heterozygous genotypes (73.36% and 63.30%) as compared to homozygous susceptible and resistant genotypes (23.3% and 10%) respective at Samiondji and Betecoucou. A correlation between phenotype resistance and presence of the domain II mutation at the voltage gated sodium channel gene was observed suggesting that this could be associated with resistance. Target site mutation and metabolic detoxification are mechanisms of resistance to pyrethroids in R. microplus tick populations from Benin.

Genetic characterization of Benin’s wild populations of Sarotherodon melanotheron melanotheron Rüppell, 1852

The Cichlid fish Sarotherodon melanotheron is typically found in West and Central African estuaries and lagoons. It represents a good candidate for promoting tilapia farming in brackish waters. Understanding the genetic diversity in its populations from the hydrographical basins of Southern Benin is primordial before designing selective breeding programs. For this purpose, 202 samples collected from four rivers of Southern Benin and were genotyped using 15 polymorphic microsatellite DNA markers. Each river was split up into three sampling sites. We found significant global linkage disequilibrium across the genome of natural populations of this tilapia species overall the loci. However, when the loci that display aberrant Wrights (FIS and FST) were removed from the data, a linkage disequilibrium was detected for the remaining 11 loci and became compatible with the null hypothesis. Null alleles explained at least 20.58% of FIS variation. We found a significant isolation by distance across subsamples. Effective population size averaged 210 individuals, with a range from 36 to 517 individuals. Assuming that 79% of heterozygote deficits are explained by sib mating lead to a rough estimate of rsm = 0.4 of mating rate between full sibs within S. melanotheron subpopulations. The fish size correlated positively and significantly with the observed FIS (r = 0.58; p value = 0.04806). Reproduction system (endogamy) in S. melanotheron could explain the strong heterozygote deficit observed. Our results provide technical guidance for efficient management of this tilapia species’ genetic resources for breeding programs in fresh and brackish waters.

Sensitivity of Different Cattle Breeds to the Infestation of Cattle Ticks Amblyomma variegatum, Rhipicephalus microplus, and Hyalomma spp. on the Natural Pastures of Opkara Farm, Benin

A study was carried out on the Opkara (Benin) cattle farm on 64 cattle of four different breeds (16 individuals per breed) from June to December 2016. During this study, three tick species were found in different numbers, Amblyomma variegatum (732), Rhipicephalus microplus (8079), and Hyalomma spp. (208), with parasitic intensity of 11.90, 126.23, and 3.25, respectively. The interracial comparison of the tick infestation between the cattle showed a significant difference (P < 0.001). However, Girolando was more infested than all the cattle breeds. Infestation of A. variegatum, R. microplus, and Hyalomma spp. on the Girolando was, respectively, 19.43 ± 2.71, 171.25 ± 23.50, and 7.12 ± 0.63, but the Borgou were less infested. Borgou breed females were more infested by A. variegatum (4.41 ± 1.14) than females Girolando (4.20 ± 0.90). The Crossbred and Azawak females were less infested (P < 0.01). The mean of A. variegatum on Borgou, Azawak, Crossbred, and Girolando calves was 1.29 ± 0.35, 0.66 ± 0.26, 1.37 ± 0.37, and 2.25 ± 0.48 (P < 0.01), respectively. The results of this study can be exploited to include genetic and nongenetic approaches to tick control.

In vitro evaluation of the acaricidal effect of vegetal oils extracted from the kernel of Thevetia peruviana and Annona muricata on the Rhipicephalus (Boophilus) microplus larvae

The objective of this work was to study the acaricide activity of oils extracted from kernels of T. peruviana and A. muricata with the hexane at different concentrations on Rhipicephalus (Boophilus) microplus larvae aged from 14 to 21 days. For this purpose, the Larva Immersion Test was performed. Twice dilutions of both oils were tested from a starting dilution of 40% to 2.5%. There were three repetitions for each concentration and for each oil. The control solution in which these larvae were treated consisted of Tween-20, diluted at 2% in distilled water. The experimental groups were stored in an incubator at 27 ± 1 °C and at 85-90% of relative humidity for 24 hours. The larvae mortality was greater than 55% in all tested groups and reached 100% at the 40% concentration for A. muricata , while the control group had a 0% mortality. The LC 50 and CL 90 obtained were respectively 4.0331% and 10.7594% for A. muricata and 7.0942% and 41.4247% respectively for T. peruviana . These results clearly indicate that these oils all have acaricidal effects on Rhipicephalus (Boophilus) microplus larvae. However, A. muricata oil is the most toxic. It can therefore be used as an effective alternative to control the Rhipicephalus (Boophilus) microplus tick and there is a high probability that it can be used for other ticks affecting cattle and even other ectoparasites in Benin and worldwide, thereby reducing the use of synthetic acaricides which are toxic to the environment and ineffective against this tick.

Effects of Hydrogeographical Origin on Zootechnical Parameters of Wild Populations of Oreochromis niloticus (Linnaeus, 1758)

The effect of geographical origin on the zootechnical parameters of tilapias is very poorly documented, unlike production systems and farming methods. In this study, the growth and survival characteristics of Oreochromis niloticus individuals were analyzed in relation with their waterway of origin, sex and age at experimental fishing. Durung the rearing, the duplicate groups were constituted keeping the 2 sexes (male vs female) separately. Fingerlings were fed using a granulated commercial fish feed (35% of proteins; 3 mm in diameter). Apart from chlorophyll «a», 3 phytoplankton and 5 zooplankton species were also available in the rearing tank. The body weight, total length, standard length, average weight gain, nutritive quotient and survival rate were similar (p>0.05) between lake Toho and Couffo river but weaker at these two waterways than Oueme river (p<0.05). The ponderal and linear specific growth rates were significantly identical between lake Toho and Couffo river but more important (p<0.001) in these two waterways than Oueme river. The majority of the individuals indicated an allometric growth (b<3), which is less desirable in fish farming. In short, 2 populations were identified: the group constituted by Oueme river and the one including lake Toho and Couffo river. It appears important to lead actions (selective breeding, crossbreeding) to improve the zootechnical performances of these local populations in order to promote their aquaculture.