Blood-feeding patterns of horse flies in the French Pyrenees.

Horse flies can mechanically transmit Besnoitia besnoiti, the agent of bovine besnoitiosis. Although previously limited to enzootic areas, especially the French Pyrenees Mountains, bovine besnoitiosis is now considered a re-emerging disease in western Europe. To improve understanding of the role of horse flies as mechanical vectors, this study investigated their blood-feeding ecology in the eastern French Pyrenees, in two high-altitude summer pastures whose main domestic ungulates were cattle, and in a wildlife park with native fauna. Species-specific PCR assays were conducted to identify the sources of blood meals: wild boar, horse, cattle (or bison), sheep (or mouflon), goat, red deer, roe deer and izard (or Pyrenean chamois). In La Mouline pasture, tabanids (N=20) fed on red deer (70%) and cattle (30%). In Mantet pasture, tabanids (N=24) fed on cattle (52%), red deer (20%), wild boar (16%), horse (8%) and sheep (4%). In the wildlife park, Tabanus bromius (N=32), the most abundant species collected, fed on red deer (85%), bison (9%) and wild boar (6%). Despite relatively high densities in both the pastures and in the wildlife park, small wild ungulates (izard, mouflon and roe deer) were not detected as a source of blood meals. Only two mixed blood meals were identified in two specimens of T. bromius: cattle/horse for the specimen collected in the pastures, and bison/wild boar for the specimen collected in the wildlife park. Our findings showed that tabanids display a level of opportunistic feeding behaviour, in addition to a preference for red deer, the latter being particularly true for Philipomyia aprica, the most abundant species collected in the pastures.

Global population structure of the stable fly (Stomoxys calcitrans) inferred by mitochondrial and nuclear sequence data.

Stomoxys calcitrans (Diptera: Muscidae: Stomoxyini), a synanthropic fly with a worldwide distribution, is recognized to have an important medical and veterinary impact. We conducted a phylogeographic analysis based on several populations from five major zoogeographic regions of the world in order to analyse population genetic structure of S. calcitrans and to trace its global dispersion. Results from mitochondrial (COI, Cyt-b and ND1-16S) and nuclear (ITS2) DNA show a substantial differentiation of Oriental populations (first lineage) from the Afrotropical, Palearctic, Nearctic, Neotropical and Oceanian populations (second lineage). The divergence time analyses suggest the separation between the two lineages approximately in mid-Pleistocene. Oriental populations are isolated and would not have participated in the colonization of other regions, unlike the Afrotropical one which seems to be the source of S. calcitrans dispersion towards other regions. Demographic analyses indicate that Oriental, Afrotropical and Palearctic regions have undergone a population expansion during late Pleistocene-early Holocene. The expansion time of this cosmopolitan species could have been influenced by continental human expansions and by animal domestication.

Landscape, population structure and genetic diversity of Stomoxys calcitrans.

To investigate whether different landscapes could affect genetic diversity and structure of the cosmopolitan diptera Stomoxys calcitrans, populations from Gabon and southern France were studied using dominant amplified fragment length polymorphism (AFLP) markers. Gabon is characterized by a forested closed landscape, and southern France by an open Mediterranean landscape. The genetic diversity between Gabon and France populations did not differ significantly (P > 0.05). Contrary to our expectation, this study shows a moderate level of genetic differentiation between these two distant countries (Fst = 0.0979) and a low genetic structure among Gabonese and French populations (Fst = 0.0291 and 0.0275 respectively). This result could indicate the capacities of S. calcitrans populations to sustain a high level of gene flow, despite geographic distance and isolation.

[Ecology of stomoxyine fulies (Diptera: Muscidae) in Gabon. II. Blood meals analysis a nd epidemiologic consequences]. / Ecologie des stomoxes (Diptera: Muscidae) au Gabon. II. Origine des repas de sang et conséquences epidémiologiques.

To determine the origin of stomoxyine fly bloodmeals (Diptera: Muscidae) in Gabon, 1,021 flies belonging to seven different species of Stomoxys were captured and dissected in the area of Makokou. In total, 798 were not blood-fed and 223 bloodmeals could be gathered on filter paper. The identification of the origin of these meals was made by amplification of mitochondrial Cytb gene, then heteroduplex technique by using the Gambian rat (Cricetomys gambianus) as driver. Samples of fauna, collected on the local market, consisted of 24 mammal and two reptile blood and muscle samples, to which it is necessary to add human samples (27 potential hosts). 19 meals could not be amplified for technical reasons, 65 were amplified, but the acquired patterns corresponded to none of the tested potential hosts. On the 139 identified meals, 55% were taken on the black-fronted duiker (Cephalophus nigrifrons) and 19% on pig. Stomoxys transvittatus, the most abundant species in Makokou, is very opportunistic: 68 % of meals were taken on six different hosts, among whom 48% on the black-fronted duiker and 32% were not identified using the panel of tested hosts. S. xanthomelas took 50% of its meals on the moustached monkey (Cercopithecus cephus) and 7% on human beings. S. calcitrans, species of anthropised areas, took 33% of its meals on human beings. These three species can therefore take bloodmeals on wild fauna and human beings. They could potentially play an important role in the emergence of zoonotic diseases. The four other species took their bloodmeals only on wild fauna and pig, the only example of domestic fauna in this study. This preliminary study must be followed up using a larger number of specimens and by increasing the diversity of the tested potential hosts.

Nonrandom partition of mitochondria in heteroplasmic Drosophila.

In order to understand the status of heteroplasmy and its evolution within the Drosophila melanogaster subgroup, cytoplasm microinjections between eggs were performed involving three lineages of Drosophila simulans, carrying the siI, siII or siIII mtDNA type, respectively, and two strains of Drosophila mauritiana carrying the maI or maII mtDNA type. Progeny of eggs from all combinations of injection were analysed. The maII or siI molecules, when provided by the donor, were never detected in the offspring of the hosts, whatever the host's mitochondrial type. Heteroplasmic flies were detected when siII, siIII or maI mitochondria were injected into any of the other cytoplasms. In the majority of cases the percentage of foreign mtDNA increased over generations, leading to a complete replacement of the endogenous mtDNA. In most cases, siII was prevalent. The stochastic processes involved in the evolution of heteroplasmic states are strongly affected by selective values of the different mtDNA types, with a clear hierarchy among them: siII has the most advantage, then siIII and maI, and finally siI and maII. In the siII/maII heteroplasmy case, the loss of maII was more rapid at a high temperature.

Properties of Drosophila simulans strains experimentally infected by different clones of the bacterium Wolbachia.

Maternally inherited bacteria of the genus Wolbachia are responsible for reproductive incompatibilities between strains of Drosophila simulans. Such incompatibilities are known in several types of crosses, including both directions of crossing between two types of infected strains, 'R' and 'S'. To determine whether the bidirectional incompatibility between R and S flies is due only to differences between their bacteria, flies from an uninfected strain have been experimentally infected with bacteria associated with each type. The incompatibility properties of experimental strains are close to those of original strains harbouring the same bacteria and therefore independent of nuclear background. Backcross experiments, however, show that the infection level of a strain depends on the nature of paternal ancestors. This is not explained by nuclear effects but is possibly the result of an interaction between the infection levels of both parents, in which the infection level of S strains is an equilibrium between a tendency for females to produce weakly infected offspring and selection of more infected eggs by sperm from infected males.

The generation of transplasmic Drosophila simulans by cytoplasmic injection: effects of segregation and selection on the perpetuation of mitochondrial DNA heteroplasmy.

Experimental transplasmic Drosophila simulans were obtained through cytoplasm microinjection between eggs carrying different mitochondrial genomes. These genomes (siII and siIII) show a 1.5% difference in their sequences. They produced a large number of heteroplasmic flies in their F1 progeny and several flies were still heteroplasmic at the eighth generation. The distribution of frequencies of mitochondrial genotypes in the offspring of heteroplasmic females suggests that the stochastic processes involved in the evolution of experimental heteroplasmy of multiple nucleotide sites are very similar to those previously described for spontaneous length heteroplasmy. In addition, the siII genome has a noticeable advantage over the siIII genome in both directions of injection. This advantage is estimated at 58% per fly generation and 5% per cell generation.

Esterases in the mosquito Culex pipiens pipiens L: formal genetics and polymorphism of adult esterases.

The genetics of two esterase loci active in autogenous adults of the mosquito Culex pipiens pipiens L. has been studied by means of starch gel electrophoresis. Three alleles at the Est-1 locus and eight at the Est-2 locus are described. Both loci have a null allele. Active alleles are codominant and there is no hybrid enzyme in heterozygotes. The Est-1 locus codes esterases preferentially hydrolyzing alpha-naphthylacetate and the Est-2 locus esterases preferentially hydrolyzing beta-naphthylacetate. Strains homozygous for both loci were selected. Linkage studies of the two loci have shown that they are not sex linked but are linked to each other, the crossover frequency being 8.6%. The polymorphism of two laboratory and two natural populations is described for both loci. Phenotypic distributions are in good agreement with Hardy-Weinberg expectations.