As a part of our investigation of the cockroach virus, isolated in 1977 and tentatively placed in the Densovirus group, studies were made of some factors governing the susceptibility of the smoky-brown cockroach, Periplaneta fuliginosa, to the virus. 1) When infected perorally with the virus, the susceptibility of the late instar nymphs seemed to be higher than that of the first instar nymphs. In the group subjected to intrahemocoeliac infection of the virus, the adults were more susceptible than the late instar nymphs, Thus, it can be said that susceptibility to the virus increases with the age of the cockroaches. 2) The first instar nymphs inoculated perorally with a higher dose of the virus were apparently retarded in their development compared with those inoculated with a lower dose. 3) The late instar nymphs were more susceptible to intrahemocoeliac than peroral infection by the virus. 4) The mean lethal time following virus infection in the late instar nymphs was shortened as the ambient temperature was increased up to 30℃. However, they were resistant to the infection when reared at a higher temperature of 35℃. The minimum effective temperature for the development of the infection was estimated to be 13℃, regardless of the inoculum sizes tested. 5) About 80% of some three hundred late instar nymphs reared in a breeding cage abruptly died over about two months. The cause was later determined to be the virus infection because of symptoms peculiar to the virus infection and successful recovery of the virus from the dead cockroaches.
View full abstract