2.1 Trombiculid mites

In 1950, he started to study trombiculid mites under the guidance of Prof. Yin-Chi Hsu. Trombiculid mites are vectors of the “sand mite fever” (scrub typhus) or chigger-borne rickettsiosis in China and Southeast Asia. This mite-borne disease results in a fatal febrile illness second to malaria. In the fields near the Shanghai Medical College, he discovered that the sand mite Odontacarus yosanoi heavily infested the rats and cats. He studied morphology, ecology, and life history of O. yosanoi both in the field and laboratory^{15, 22, 54}. In 1957, Prof. Wen^{8, 9} from China and Lipovsky et al. (1957) from USA independently discovered that sand mites produce spermatophores in vitro. Their findings overturn Wharton & Fuller's hypothesis of direct mating between males and females (Wharton & Fuller 1952). Prof. Wen designed a perpendicular hole in the centre of chigger-rearing tube to observe better the lateral spermatophore transmission and the indirect mating process of O. yosanoi^{15, 22}. Their studies filled the gaps in the understanding of sand mites' life history³⁷. Apart from reproduction, Prof. Wen also discovered the galeal organ, a dome-like sensilium, at the tip of all larval mouthparts.

In 1984, Prof. Wen published a monograph, “Sand mites of China”. This book is one of the most distinct publications regarding mites, comprehensively interpreting the sand mite descriptions in Ge Hong's “Baopuzi,” written in the Eastern Jin Dynasty. “Sand mites of China” is also the first symposium comprising original descriptions of sand mite species and the distribution records of reported sand mite species in China, cited in international literature, Zoological Papers, and Biological Abstracts. Many aspects of his classification scheme are currently used and quoted by recent studies (e.g. Nelsen et al. 2021).

The monograph “Sand mites of China” comprised 4 chapters. Chapter I consisted of the articles concerning the taxonomy of the family-group and genus-group of sand mites of China. This chapter began with a retrospective survey of ancient Chinese literature in the memory of Ge Hong, the earliest scientist in Acarology. Then, using numerous specimens obtained from China, the taxonomic status of the family-group taxa of sand mites was revised. Under the subfamily Walchiinae, 4 tribes were proposed: Walchiini, Schoengastiellini, Gahrliepiini, and Intermedialiini. The validity of the taxa of the genus-group established previously by Chinese trombidologists was revised and commented: (1) Globularoschoengastia (Chen & Hsu 1955) was a junior synonym of Helenicula (Audy 1954); (2) Paradoloisia (Chen & Hsu 1965) remained as a valid generic name; (3) Multisetosa (Hsu & Wen 1963)³⁸ was a well-defined and valid genus; (4) subgenus Intermedialia (Yu, Yang & Wu 1979) was elevated into a new genus; (5) Huabangsha (Wen, Yu & Yang 1980)⁶⁹ was accepted as a valid genus. This chapter established 3 new genera and 2 new subgenera of sand mites and 1 subgenus was elevated to a new genus, as mentioned previously. The phylogenetic relationships between 3 hirsute genera, Odontacarus, Multisetosa, and Zhongguosha were discussed. To facilitate study by junior readers, key to the known Chinese families and genera of sand mites, including 2 families, 3 subfamilies, 6 tribes involving 41 genera, and 12 subgenera, were given at the end of Chapter I.

Chapters II and III comprised descriptions of new species of sand mites. A total of 150 new species, including 10 new subspecies collected from 14 provinces, 1 municipality, and 4 autonomous regions in China, were described. Chapter IV included a checklist of the known species of sand mites in China described before the end of 1980. A total of 353 species of sand mites, including 13 subspecies, were listed, along with their hosts and geographical distributions nationwide. The host index consisted of 166 species of animals belonging to 21 orders, including crustaceans, reptiles, birds, humans, and other mammals.

2.2 Gamasid mites

In 1958, the hemorrhagic fever epidemic broke out in various parts of China. Prof. Wen was assigned to control the outbreak in Anhui, and he was primarily responsible for the investigation and control of rodents and mites in the epidemic area. He confirmed that the disease was transmitted through multiple channels, and the spread risk of gamasid mites was not high. The Anhui Provincial Party Committee commended him for his taxonomic updates and descriptions of three new species belonging to the genus Eulaelaps, denying the existence of E. stabularis in eastern China. Prof. Wen studied the sensilla of gamasid mites that provided insights into their taxonomy⁵⁶. When controlling the outbreak, he discovered a new species, Leptotrombidium linhuaikongense,²⁵ in the epidemic area, which is currently known as the vector of sand mite fever transmitted from Huaibei (areas north of Huai River) to Luxi (western parts of Shandong).

2.3 Dust mite allergies

In 1972, Prof. Wen led the research on the relationships between dust mite allergies and asthma, rhinitis, and dermatitis in China. He successfully developed the vaccine for dust-mite Dermatophagoides farinae and applied it for diagnosis and desensitizing in more than 800,000 patients on the Chinese mainland from 1975. The vaccine is simple and effective and has been commercialized. Prof. Wen's vaccine of D. farinae is renowned for its potency against dust mite allergies. His vaccine's potency is more robust than that of Food and Drug Administration (FDA) (USA) and ALK (Denmark)⁴¹⁰. The results of abdominal pills treatment for allergic rhinitis with best efficacies were published in 2018⁴³⁷. In 1986, Prof. Wen became a consultant for a particular project on infection and allergy by National Institute of Allergy and Infectious Diseases, NIH in the United States. Prof. Wen^{408, 409} was the Chinese delegate of three international workshops on mite allergy sponsored by the World Health Organization in 1987 (Frankfurt, Germany), 1990 (Oxford, England), and 1995 (Cuanca, Spain) (International Workshop 1988; Platts-Mills et al. 1992). In addition to being invited as the special guest to more than 40 national and international academic conferences, he also attended more than 20 lectures in 15 different continuing education classes to improve his clinical skills in preventing and treating mite-induced diseases. He was invited to write several influential review books with broad coverage on dust mite allergies and other topics, with a special chapter on disease-transmitting mites and ticks in clinical fields, including pediatric diseases, infectious diseases, tropical diseases, and epidemiology. He popularized the knowledge of dust mites, especially for specialists, doctors, and their patients, and developed and promoted strategies for preventing and controlling dust mites.