Resistance to Nucleopolyhedrosis Virus of Breeding stocks in Japanese Tusser, Antheraca Yamamai, GUERIN-MENEVILLE

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Improvement of the crop productivity was studied by attempting breeding of disease-resistant stocks and by epizootiological approach to nucleopolyhedrosis virus infection which deteriorates the yield of crops .1 . Female Japanese tussers (n=31) and male Chinese tussers,Antheraea pernyi, GUERIN-MENEVILLE (n=49) were mated to compare the economical character of resultant! hybrids with those of Japanese tussers. (1) Despite poor fertilization ratios in mothers, larvae developed well and had high resistance to NPV-infction. Both the weight and percentage of cocoon shells were also higher. Using the <F_1> hybrids, 3 offspring combinations were obtained ; <F_1> X Japanese tusser, Japanese tusser X <F_1> and <F_1> X <F_1> . (2) Hybrids in the 2nd and later generations demonstrated no such remarkable differences in traits as the <F_1> hybrids. However, abnormality was found in the larvae of the 3rd instar which developed blackish dots on the lateral aspect of the 2nd to 4th segments. This breeding stage corresponds to the time of testicular mytotic activity which contained chromosomal heteroploidy.2 . The biological quality of larvae and quality of cocoon filament in the disease-resistant stock (SR) and body-color mutant stock (MT) were compared with controls. (1) The hatchability and cocoon productivity were higher in both SR and MT than controls. (2) SR females produced a larger weight of cocoon filament. Male and female MT produced filament that excelled in strength and stretchability.3 . The cause of poor crop was investigated in relation to pathogens of nucleopolyhedrosis occurring in field rearing. (1) A large amount of pathogens were isolated and recovered from the leaves and stems of oak, Quercus acutissima which caused a prevalance of nucleopolyhedrosis. (2) On the basis of (1), a pattern of pathogen propagation by inhabiting insets was postulated.