The impact of mulberry silkworm diseases (Bombyx mori L.) on the efficiency of cocoons in Poland.
Comparison of cocoon efficiency in mulberry silkworm farms in Poland and in the leading countries in this field, like japan, Italy, Russia and others, points, that Polish breeders achieve, on average, only 50% possible breeding efficiency. This is the case of cocoon collection in Poland, per gram of grena sent to breeders. Nevertheless, there are many breeders in Poland, who will match their harvest, and even exceed the average cocoon harvest in the leading silkworm rearing countries (Golański 17). It is also known, that the same breeds bred abroad and in Poland are often characterized by higher values in Poland, than abroad, especially when it comes to the size and weight of the cocoons, the silk content in the cocoons and the length of the unwound thread in the cocoon.
A few years after the World War II, the Japanese began to produce high-value multiple hybrids (polytherapy). The performance of them, especially industrial, compared to the hitherto reproduced races and their hybrids, increased by 50%. These hybrids, under a Japanese license, Italians started to produce them in the 1950s and supply them to other European countries (28). Also Poland from 1958 r. uses greny polyhybrids of Italian and Japanese origin. The Japanese grena turned out to be better and that's why we've been importing recently 33 only from Japan. (36, 48, 53, 54). At the same time, work began at the Natural Silk Laboratory in Milanówek and the Silk Breeding Plant in Krakow on the selection of appropriate breeds and the production of their own polyhybrids. (5, 6, 48).
Obtaining positive results would make Poland independent of the import of foreign grena and, moreover, it could become the basis for the expansion of our grenar industry, because other socialist countries would gladly buy a good gree of polyhybrids from us. In the current state of research, these prospects are only a vision of the future.
One of the reasons for low breeding efficiency, and thus industrial, Polish silk industry is undoubtedly the frequent appearance of diseases in farms and the lack of effective measures to combat them. The amount of losses incurred by breeders, PZU and the industry as a result of diseases in farms is not yet known. An initial attempt to present this issue in a statistical framework are the master's theses of the students of the Military University of Life Sciences in Krakow, carried out at the Department of Jedwabnik Breeding of the Institute of Medicine under the supervision of the author, on the frequency of disease occurrence in Poland in the years 1956—1960, (10, 23, 34, 37, 52) and the author (20, 21, 22). This work is an introduction to the development of the second stage, i.e.. estimating material damage caused to farms by diseases.
Among the mulberry silkworm diseases occurring in Poland, jaundice causes the greatest losses, deadness and rot. Consumption causes much less damage, muscardine and pehryna.
Jaundice (nuclear polyhedrosis) is caused by the bacterium Borrelincvirus bombycis P., which enters the hemolymph via? damaged skin or through externally infected mulberry leaves through the digestive tract. In the nuclei of cells of various tissues, this virus produces protein inclusions in the form of polygonal plaques called polyhedra (11, 14, 16, 18, 21, 27, 32, 49). The greatest danger of these germs lies in this, that they can get through the eggs, and possibly sperm, pass from generation to generation in a latent state and activate their destructive effects, depending on the favorable conditions for their reproduction (4, 9, 50).