The paper considers horizontal transmission routes of baculovirus infection in the gypsy moth (Lymantria dispar L.). The original method for modeling natural processes in controllable conditions allowed one to estimate the influence of factors on the occurrence of epizooties. The authors investigated 3 possible models of virus transmission from infected to uninfected gypsy moths: 1) infected and test caterpillars were kept and fed together (a complex route); 2) those which were in the immediate vicinity, but deprived of eating together (an aerial route); 3) test caterpillars were fed on the leaves on which infected caterpillars had eaten (an oral route). The investigations have shown that the complex and oral routes out of the considered models may be considered to be effective infection transmission routes for the horizontal spread of epizooties. Furthermore, the availability of sufficient amount of infected caterpillars in the population leads to a reduction in the resistance of healthy insects to other diseases. Thus, by taking into account the capacity of larvae for passive migration, the purpose of insecticidal treatment is to set up a few infection foci that will be a source for the spread of epizootias and contribute to an overall viability reduction of a pest population.