Abstract
A series of studies have been carried out by us on the horse fly, Tabanus iyoensis Shiraki, which is a serious pest in certain areas in Toyama Prefecture. The present study mainly deals with the results of field and laboratory observations in its life history, with emphasis on the possibility of its autogenous reproduction. The results of dissection of females caught with both dry-ice traps and with insect nets have revealed that their parous rates are surprisingly high (93%, 543/584) even in the early season of their appearance (late July to early August). It is presumed from these observations that the horse fly mostly deposites autogenous eggs before taking the first blood meal. It has been also confirmed that the female horse flies reared from pupae in the laboratory mostly deposit eggs before taking a blood meal, even when the blood source is available. However, the blood meal seemed to be necessary for producing the second and the subsequent batches of eggs. The appearance of surprisingly large numbers of this horse fly seems to be due mainly to the involvement of such autogenous reproduction, especially in areas where almost no blood sources are available. Such an unusual mode of reproduction as the horse fly seems to be sufficient for maintaining their population density in large areas, and makes its control to be difficult.
