Zoonotic onchocerciasis, an emerging human infection caused by animal parasitic Onchocerca species, has recently increased worldwide. We have investigated the transmission of Onchocerca japonica, a parasite of wild boar and a causative agent of zoonotic onchocerciasis in Japan. In this article, the search for the natural vectors (blood-sucking insects) of O. japonica is reviewed. Inoculation experiments demonstrated that six anthropophilic black fly species are suitable for the development of O. japonica microfilariae to the infective larvae. To determine the vector of O. japonica, natural infections of wild-caught black flies with filarial larvae were investigated. Morphometric and molecular identification of the infective larvae detected showed that anthropophilic Simulium bidentatum is a natural vector of O. japonica. In addition, metabolites of the four larval stages of O. japonica, i.e., microfilariae in naturally infected wild boar, and first-stage larvae, second-stage larvae, and third-stage larvae (infective larvae) in experimentally infected black flies were analyzed. Multivariate analysis of the data showed a clear distinction between the four larval stages and hydroxylamine was proposed as a potential biomarker candidate to detect infective larvae in black flies. Finally, a study on speciation of black flies is reviewed by focusing on the Simulium rufibasis subgroup in Asia.

The blood-sucking habits of female black flies are responsible for considerable deleterious effects on humans and their economic welfare. With the aim of controlling black flies in the upper reaches of the Ukawa River in Kashiwazaki City, Niigata Prefecture, Japan, the present study was conducted to determine the flight densities of adult black flies by using sticky-board traps with dry ice set over 24 hours at 30 sites in the Betsumata area from June to October 2021 with citizen cooperation. The results were that a total of 4,232 individual adult black flies were captured from all sampling sites during the investigation period. The month in which the most black flies were captured was August 28–29, with 1,496 individuals, followed by October 23–24 with 1,434 individuals. The average number of black flies per site was 28.2 individuals/trap during the investigation periods. Many black flies tended to be captured around the Jojoimogawa River and around the mountains which surround the Betsumata area, while the density of black flies in rice paddies was low. It was presumed that the place of emergence and the resting/hiding place did not match. It is important to take measures against black flies in their resting/hiding places.

Aedes albopictus is known to expand its range into northern Japan; however, its likely invasion to Hokkaido is concerning. Aedes albopictus larvae were first collected from Aomori Prefecture in 2015. Therefore, we have conducted continuous mosquito surveys in Aomori and Hokkaido areas since 2016 to confirm the expansion and invasion of Ae. albopictus into new areas. Both the adults and larvae of Ae. albopictus were collected from Aomori City and this species was confirmed to continuously expand its range. In contrast in Hokkaido, Ae. albopictus was not found in Hakodate, Otaru, and Sapporo cities, but Armigeres subalbatus, which has never been reported in Hokkaido, was collected for the first time. These results revealed that another exotic mosquito species, Ar. subalbatus, was invading a new area, and there was concern that Ae. albopictus could also invade the Hokkaido region in the future.

The numbers of Tabanus nipponicus and T. humilis collected between 2022 and 2024 increased significantly compared to those collected between 2005 and 2009 in the Arimine area of Toyama Prefecture, Japan. This increase is thought to be associated with the invasion of Sika deer, which serve as a blood source for these flies.

New distributional records of Lispe aquamarina and Lispe pseudohirsutipes (Diptera: Muscidae) from the Kanto region, Japan, are reported.