[Study of mortality agents of silk worms in Dough Abad]

ABSTRACT

For investigation of causes of silkworm mortality, the sick larva specimens in different levels of growth examined for parasite, viral, fungal and bacterial diseases. The samples included some dead larva and bed materials contained eggs, leaves and stool which were examined ordinary diagnostic methods. The complementary tests were also used for all cases. In wet smear prepared from intestine wall, a kind of protozoa spore of Microsporidia phylum was observed that was not the agent of pebrin disease, and some budding cells [yeasts] were seen as well, which identified as Saccharomyces cerevisiae. There were many polyhedra forms in smears of hemolynph that were stained with methylen blue dying and seen with ordinary microscope, diagnosed as Polyhedrosis or Grasserie disease [NPV]. for the purpose of diagnostic reconfirmation, the polyhedra was injected to healthy larva. The bacterial agent including Streptococcus [delta] Hemolytica as digestive tracts disease agent, staphylococcus aureus, and Serratia marcescen as septicemia agents and Bacillus turingensis the agent of Sotto disease, were separated. In general the incidence of these diseases showed the unsuitable conditions in sericultures that can be depends on poor disinfection, lack of proper feeding and deficiency of temperature and humidity. Improvement in rearing techniques, using of appropriate rearing room and equipments, maintenance of hygienic conditions during rearing, improvement of disinfection methods, the quarantine of the silkworm seeds and using of resistant varieties of silkworm to diseases can decrease out-breaks