Epizootic Diseases of the Nun Moth (Lymantria monacha L.) and Possibilities of its Microbiological Control

1989

71 S.

23 Abb., 19 Tab., 98 Lit. Ang., Pl, Zfsg. En, Pl, Ru

Unselbständiges Werk

200027417

During the outbreak of the nun moth, we conducted studies on epizootic diseases of caterpillars and on the influence of some factors on the induction of the latent form of the virus of nuclear polyhedrosis of caterpillars (tree-top disease). We also studied the possibilities of the pest control with the use of microbiological insecticides. Field observations and registration of viral diseases showed that in the years 1981-83 in territories of mass appearance of the nun moth the nuclear polyhedrosis caused by Baculovirus efficiens occurred in the populations in caterpillars. The disease developed only in caterpillars feeding on spruce, larch and deciduous trees, but it did not develop in caterpillars living in pine stands, what would indicate that pine needles contain compounds inhibiting the development of B. efficiens in the nun moth. The polyhedrosis virus is known in European forest literature concerning calamitous appearance of the nun moth in 19th and the first half of 20th century as factor regulating the number of the pest in spruce stands. Now, when the nun moth changed the host plant and occurs mainly on pine, B. efficiens lost its importance. In pine stands, where the number of the pest was high and no control treatments were performed, in cases of limited quantity of food, bacterial epizooties developed in weakened caterpillars. They were caused by Gram-negative intestinal microflora. Also diseases with unexplained etiology, manifested by inhibition of feeding and drying-up of caterpillars in spite of abundance of suitable food, had epizootic character. No microorganisms were found in bodies of diseases and dead caterpillars. Observations on the induction of the latent form of B. efficiencs, made during the rearing of about 30,000 caterpillars, showed that the virus became active in about 1.24% of individuals. The frequency of B. efficiens increased with the number of eggs of the nun moth found on one tree and it was highest in caterpillars coming from territories of the 2nd year of outbreak duration. Results of three trials of then nun moth control with B. efficiencs products prepared in laboratory proved that the mortality of caterpillars was differentiated, in dependence on the host plant, and amounted to 32-68% on pine and 82% on spruce. In the case of the nun moth control with commercial B. thuringiensis products, better results of the treatments were obtained in pine stands (80-100%) than in mixed pine-spruce stands (30-80%).