Abstract
In this paper, some effects of a high temperature on the incidence of the cytoplasmic polyhedrosis of the silkworm were investigated, with special consideration on effects of the period in a high temperature.
The results obtained are summarized as follows:
1) When rearing temperature was changed. i.e., from a high temperature (35°C) to a low temperature (25°C) after the virus inoculation, the longer the period in a high temperature, the lower the incidence of cytoplasmic polyhedrosis. The similar results were obtained when rearing temperature was changed from 25°C to 35°C.
2) In order to know the early initiation of virus multiplication, the adsorption ability of virus to the midgut cell at a different temperature was examined. Same quantities of the midgut samples from healthy silkworms were obtained and they were added to continuous diluted virus suspension for 3 hours at 25°C or 35°C. After centrifugation, the supernatant was injected into another silkworm larvae to estimate the virus titration. Hemagglutination test was also used. One hour after virus injection to the silkworm larvae, the hemolymph or midgut homogenate from them was injected into another silkworm larvae and the amount of virus was estimated with bioassay and with precipitin ring test. From these results, it was ascertained that there were no different adsorption abilities of midgut to the virus between 25°C and 35°C.
3) The extraction of the interferon like substance (s) was tried by the modified method of NAGANO et al. (1966) from the silkworm larvae reared at a high temperature, but no activity was recognized.
4) From these results, it is assumed that the cause of suppression of the virus multiplication at a high temperature is neither virus adsorption process to the midgut cell, nor the product of interferon like substance(s) in the silkworm.
The problem in which stage the virus multiplication is suppressed at a high temperature remains yet to be determined in the near future.
