Abstract: Objective To identify the morphological and molecular characterization of mite Tyrophagus putrescentiae. Methods T. putrescentiae mites were collected from the flour stored over 1 year and the life cycle was maintained in the lab. The larval, nymph and adult mites and the eggs were observed under optical microscope and scanning electron microscope (SEM). The DNA was extracted from the mites, the cytochrome oxidase subunit Ⅰ(cox1) and internal transcribed spacer(ITS) genes were amplified by PCR. The PCR products were ligated into the vector pMD19-T, then transformed into Escherichia coli. The inserts in the positive clones were DNA sequenced. The obtained DNA sequences were analyzed by DNAStar software and performed BLAST alignment analysis against mite sequences in GenBank. The phylogenetic tree was constructed accordingly. Results The body of T. putrescentiae was oval shaped with a smooth, colorless and translucent surface. The pincers and feet were brownish, and the setae on the body were slender but not stiff. Morphological structures of T. putrescentiae, including legs, setae, external genitalia and accessories, could be clearly identified under SEM. The larva had three pairs of legs, the nymph and adult had four pairs of legs and one pair of chela. The body was composed of three segments. Within Ⅳ coxa, the reproductive organ can be discovered, the lateral plates bended outward to form a "herringbone" shape, and the anus was slender and located in the posterior half with longer anal hair beyond the body. The hair d1 is short, the d2 is longer, and hair hi is longer than the hair he. The clearly discovered hair pa in the posterior is beyond the body. The hair vi and outer hair ve were found in the forefoot, the hair sci was longer than that of the sce, and the outer hair o1 of the knee was slightly longer than that of o2. The PCR products of ITS amplified from T. putrescentiae was 1 852 bp and cox1 was 469 bp in length. BLAST search confirmed that cox1 sequence matched the sequence of T. putrescentiae. The A+T content of cox1 sequence was 65.7%. The phylogenetic tree based on cox1 gene sequence showed that the T. putrescentiae is genetically close to T. longier with sequence similarity of 91.5%. The A+T content of ITS sequences was 53.6%. The phylogenetic tree based on ITS showed that the sequence of ITS of T. putrescentiae was quite different from that of other Acarida, with the sequence similarity of 37.7%-41.8%. Conclusion The mites collected from the stale flour were identified as T. putrescentiae based on their morphological characterization and amplified cox1 and ITS gene sequences.

Key words: Tyrophagus putrescentiae, Morphology observation, Molecular characterization