Abstract:

Objective To observe the morphological characteristics of adult Histiostoma feroniarum under the electron microscope, and to study the genetic relationship between this species and other mite species of Acaridae. Methods The adult stage of H. feroniarum was isolated from the culture, and its external morphological features were observed using scanning electron microscopy (SEM), followed by extracting the mite DNA, for amplifying the cytochrome oxidase subunit 1 (cox1) and internal transcribed spacer (ITS) by PCR. The ITS and cox1 gene was sequenced and compared with the other 8 Acaridae species in GenBank. The phylogenetic tree was constructed by the maximum likelihood method. Results Under the electron microscope, the ventral epidermal protrusions of the mites were more developed. The epidermal protrusions of foot I healed into the chest plate, and the epidermal protrusions of foot Ⅱ extended to the centre and were not connected. There were 2 pairs of chitinous rings on the ventral surface, and the male adults were located between the Ⅱ-Ⅳ basal ganglia. The first pair of chitin rings of the female mite was located between the foot Ⅱ and Ⅲ, and the last pair of chitin rings were located at the level of the foot Ⅳ basal ganglia. Compared with the light microscope, the structures of male reproductive folds, leaflets and penis were clearer under the electron microscope. The cox1 and ITS sequences were obtained by PCR amplification, which was 539 bp and 1 633 bp. The ITS sequence similarity comparison results showed that the sequence similarity between H. feroniarum and Blomia tropicalis (GenBank accession no. KC215362) was the highest, which was at 90.41%, and the sequence similarity with other Acaridae species was 83.33%-89.73%. The cox1 sequence alignment showed that the highest sequence similarity was 83.55% between H. feroniarum and Lepidoglyphus destructor (GenBank accession no. MT075728), and the sequence similarity with other Acaridae species ranged from 79.78%-82.12%. The phylogenetic tree constructed based on ITS and cox1 sequences has differences in topological structure. showing that H. feroniarum is a single branch, but not at the same branch of other Acaridae species, which is likely consistent with morphological classification. The phylogenetic analysis based on ITS showed that H. feroniarum and Rhizoglyphus robini were clustered as a branch, which differs from morphological classification. Conclusion The morphological structure of male and female H. feroniarum could be clearly observed by scanning electron microscopy. Phylogenetic analysis of cox1 sequence reveals relatively distant genetic relationship seen between the H. feroniarum and other acaroid mites.

Key words: Histiostoma feroniarum, Scanning electron microscopy, External morphology, Phylogeny