Comparative mitogenome analyses of twelve non-biting flies and provide insights into the phylogeny of Chironomidae (Diptera: Culicomorpha).

The family Chironomidae is represented by seven subfamilies in China, among which Chironominae and Orthocladiinae are the most diverse. To gain a better understanding of the architecture and evolution of the mitogenomes of Chironomidae, we sequenced mitogenomes of twelve species (including two published species) of the two subfamilies Chironominae and Orthocladiinae, and comparative mitogenomic analyses were performed. Thus, we identified highly conserved genome organization of twelve species with regard to genome content, nucleotide and amino acid composition, codon usage, and gene characteristics. The Ka/Ks values of most protein-coding genes were far smaller than 1, indicating that these genes were evolving under purifying selection. Phylogenetic relationships between the family Chironomidae were reconstructed using 23 species representing six subfamilies, based on protein-coding genes and rRNAs using Bayesian Inference and Maximum Likelihood. Our results suggested the following relationship within the Chironomidae: (Podonominae + Tanypodinae) + (Diamesinae + (Prodiamesinae + (Orthocladiinae + Chironominae))). This study contributes to the mitogenomic database of Chironomidae, which will be significant for studing the mitogenome evolution of Chironomidae.

Cloning and characterization of Methoprene-tolerant (Met) and Krüppel homolog 1 (Kr-h1) genes in the wheat blossom midge, Sitodiplosis mosellana.

Juvenile hormone (JH), a growth regulator, inhibits ecdysteroid-induced metamorphosis and controls insect development and diapause. Methoprene-tolerant (Met) and Krüppel homolog 1 (Kr-h1) are two proteins involved in JH action. To gain some insight into their function in development of Sitodiplosis mosellana, an insect pest undergoing obligatory larval diapause at the mature 3rd instar stage, we cloned full-length complementary DNAs of Met and Kr-h1 from this species. SmMet encoded a putative protein, which contained three domains typical of the bHLH-PAS family and eight conserved amino acid residues important for JH binding. SmKr-h1 encoded a protein showing high sequence homology to its counterparts in other species, and contained all eight highly conserved Zn-finger motifs for DNA-binding. Expression patterns of SmMet and SmKr-h1 were developmentally regulated and JH III responsive as well. Their mRNA abundance increased as larvae entered early 3rd instar, pre-diapause and maintenance stages, and peaked during post-diapause quiescence, a pattern correlated with JH titers in this species. Different from reduced expression of SmMet, SmKr-h1 mRNA increased at mid-to-late period of post-diapause development. Topical application of JH III on diapausing larvae also induced the two genes in a dose-dependent manner. Expression of SmMet and SmKr-h1 clearly declined in the pre-pupal phase, and was significantly higher in female adults than male adults. These results suggest that JH-responsive SmMet and SmKr-h1 might play key roles in diapause induction and maintenance as well as in post-diapause quiescence and adult reproduction, whereas metamorphosis from larvae to pupae might be correlated with their reduced expression.

Modeling the global distribution of Culicoides imicola: an Ensemble approach.

Culicoides imicola is a midge species serving as vector for a number of viral diseases of livestock, including Bluetongue, and African Horse Sickness. C. imicola is also known to transmit Schmallenberg virus experimentally. Environmental and demographic factors may impose rapid changes on the global distribution of C. imicola and aid introduction into new areas. The aim of this study is to predict the global distribution of C. imicola using an ensemble modeling approach by combining climatic, livestock distribution and land cover covariates, together with a comprehensive global dataset of geo-positioned occurrence points for C. imicola. Thirty individual models were generated by 'biomod2', with 21 models scoring a true skill statistic (TSS) >0.8. These 21 models incorporated weighted runs from eight of ten algorithms and were used to create a final ensemble model. The ensemble model performed very well (TSS = 0.898 and ROC = 0.991) and indicated high environmental suitability for C. imicola in the tropics and subtropics. The habitat suitability for C. imicola spans from South Africa to southern Europe and from southern USA to southern China. The distribution of C. imicola is mainly constrained by climatic factors. In the ensemble model, mean annual minimum temperature had the highest overall contribution (42.9%), followed by mean annual maximum temperature (21.1%), solar radiation (13.6%), annual precipitation (11%), livestock distribution (6.2%), vapor pressure (3.4%), wind speed (0.8%), and land cover (0.1%). The present study provides the most up-to-date predictive maps of the potential distributions of C. imicola and should be of great value for decision making at global and regional scales.

Mitochondrial Genomes Provide Insights into the Phylogeny of Culicomorpha (Insecta: Diptera).

Culicomorpha is a monophyletic group containing most bloodsucking lower dipterans, including many important vectors of pathogens. However, the higher-level phylogenetic relationships within Culicomorpha are largely unresolved, with multiple competing hypotheses based on molecular sequence data. Here we sequenced four nearly complete mitochondrial (mt) genomes representing four culicomorph families, and combined these new data with published mt genomes to reconstruct the phylogenetic relationships of all eight extant culicomorph families. We estimated phylogenies using four datasets and three methods. We also used four-cluster likelihood mapping to study potential incongruent topologies supported by the different datasets and phylogenetic questions generated by the previous studies. The results showed that a clade containing Ceratopogonidae, Thaumaleidae and Simuliidae was the sister group to all other Culicomorpha; in another clade, the Dixidae was basal to the remaining four families; Chaoboridae, Corethrellidae and Culicidae formed a monophyletic group and the Chironomidae was the sister group to this clade; Culicidae and Corethrellidae were sister groups in all trees. Our study provides novel mt genome data in Culicomorpha for three new family representatives, and the resulting mt phylogenomic analysis helps to resolve the phylogeny and taxonomy of Culicomorpha.

The complete mitochondrial genome of Dixella aestivalis (Diptera: Nematocera: Dixidae).

Dixidae, meniscus midges, belong to the suborder Nematocera of the order Diptera. The family includes 197 known species classified in nine genera. The complete mitochondrial genome of the Dixella aestivalis (Meigen) from the United Kingdom is reported here, along with its annotation and comparison with the genome of an unidentified species of Dixella from China. The circular genome consists of 16 465 bp and has a gene content consisting of 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes and a non-coding, A + T-rich, control region. The mitochondrial genome of D. aestivalis can be used to identify genetic markers for species identification, and will be valuable for resolving phylogenetic relationships within the genus, family Dixidae and suborder Nematocera.