Studies On The Development Of Camel Parabronema Skrjabini In Its Vector-Horn Flies

Camel parabronemosis is a kind of nematodiasis which is caused by parabronema skrjabini parasitized in the camel abomasums and may bring serious damage to the camel industry, and its vectors are Haematobia irritans and Haematobia titillans. In order to ensure the development process of parabronema skrjabini in horn flies, a large number of suspected larvae of horn flies were collected from camel dung and cow dung in the camel living environment and identified by the classification criteria for the horn fly larvae and molecular biology method. Later, a large number of different instars larvae of horn flies were dissected to look for the larvae of parabronema skrjabin, then the larvae were identified by the molecular biology method, and the infection rate of parabronema skrjabin in the larvae of horn flies were counted and the morphological characteristics were observed. Meanwhile, the 18S rDNA gene sequences of H. irritans and H. titillans in Inner Mongolian area were cloned and the homologies were compared with nine insects of diptera which had been logged in the GenBank. Besides, the phylogenetic tree was constructed by using their whole sequence and their most conservative homologous region of 18S rDNA gene sequences to determine the position of two kinds of horn flies in diptera, and it also provided the basis for the correlational research of the differences of insects of different genera in diptera and the molecular phylogenetic features. The results were as follows:1) The larvae of flies collected from camel dung and cow dung in camel living environment had been indientified to be larvae of horn flies. Modified phenol/chloroform extraction was the most effective DNA extraction method for the identification of horn fly larvae by the molecular biology method.2) Horn flies were infected by the parabronema skrjabini egg when it was in the larvae stage, and the 1st,2nd,3rd larvae of horn flies all could be infected, while the infection rates were 4.48%,5.66% and 4.78%, respectively. The morphological structures of parabronema skrjabini larvae were similar under the light microscope in different larvae of horn flies. Their headend was finely rounded, and stylet was apparent and located in the top; Tapering tail bent to the ventral, and the anal opening was at the end of the worm; its internal structure was simple, and the esophagus can be seen, which was linked with the intestine, and it can be separated into muscle ministry and glandular ministry.3) The 18S rDNA sequences length of H.irritans and H. titillans were 1984bps, and the homology between them was 96.4%. There were 73 recognition sites. The 18S rDNA gene sequences of H. titillans were reported for the first time in the world in this article. There were three highly conserved homologous regions in the 18S rDNA gene sequences of 11 kinds of diptera insects that included two kinds of horn flies, which covered the sequence from 320bp to 693bp,848bp to 1181bp and 1606bp to 1849bp in 18S rDNA gene sequences of H.irritans, respectively, while the first section of the homologous regions was the most conservative. Classification by the most conservative homologous region of 18S rDNA gene sequences to construct phylogenetic tree of 11 kinds of diptera insect was more in line with traditional morphological classification than classification by the whole sequence.The parabronema skrjabini larvae were isolated and identified for the first time from the horn fly larvae, and their morphological characteristics were described. The results not only filled the blank of the above research at home and abroad, but also laid the foundation for finging out the decelopment process of parabronema skrjabini in its vector, horn flies.