The aim of the research was to assess a possible reaction of forest phytophages with different types of seasonal development on climate change. The patterns of seasonal development for foliage browsing insects and possible changes with temperature increase were analyzed considering hibernating stage and the presence of summer diapause. Analysis shows that forest phytophagous insects can adapt to climate change by the acceleration of development, expanding the range of host plants, changing the location of individual stages, or spreading the range. Species that are monophages throughout their current range will remain monophages. The survival rate and harmfulness of phytophagous insects will depend on their synchronicity with the appearance of foliage and entomophages. The harmfulness of phytophages will increase with an increase in their voltinism and with an increase in the vulnerability of trees under conditions of aridity and anthropogenic pressure and will decrease as a result of a decrease in the size of insects and their fertility during rapid development. Hibernation of individuals at stages that are not adapted to new combinations of temperature and photoperiod can also be negative results of climate change.