Effect of treatment using nuclear polyhedrosis virus on Lymantria dispar in field experiments in central Slovakia

Two strains of the nuclear polyhedrosis virus of the gypsy moth, Lymantria dispar, are compared in field applications on experimental plots. With dosages 2 × 10¹¹–10¹² PIB ha⁻¹ received, corrected mortalities of larvae varied from 70% to 92%. At the same time, natural mortality of untreated populations ranged form 27% to 55% at the peak of the outbreak. The total reduction with ‘Gypchek’ the U.S. commercial formulation, reached 95%, compared with 93% after application of non-formulated material of a local strain under identical conditions. The American strain of NPV of the gypsy moth does not differ significantly in its effect from the local NPV on European populations of the gypsy moth.