Proceedings 2021, https://doi.org/10.3390/IECE-10373 Proceedings Pros and Cons of Climate Change for Forest Phytophagous In- sects † Valentyna Meshkova 1 Ukrainian Research Institute of Forestry & Forest Melioration, Pushkinska str. 86, 61024, Kharkiv, Ukraine; Valentynameshkova@gmail.com * Correspondence: Valentynameshkova@gmail.com † Presented at the 1st International Electronic Conference on Entomology (IECE 2021), 1–15 July 2021; Available online: https://iece.sciforum.net/. Abstract: 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. Keywords: foliage browsing insect; entomophage; seasonal development; photoperiod; harmfulness 1. Introduction Climate change is to increase the temperature, CO2 concentration, the frequency of drought, fires, and hurricanes [1]. Of these factors, the greatest value for insects has a temperature that affects their survival and development directly and indirectly through the availability and quality of food [2–4]. Within the limits between the lower and the upper thresholds of temperature, the survival, the rate of development of insects as poikilothermic organisms depend on temperature [3]. This suggests that the acceleration of insect development will bring to increase the number of generations. This will negatively affect the health condition of trees, which will be weakened by the action of the above-mentioned and other factors [5]. At the same time, in the zone of a temperate climate with winter, spring, summer, and autumn, insects are adapted to hibernate in the most protected places and in the least vulnerable stage [6]. This is one of the reasons for the predominance of monovoltine forest phytophages. The signal to change the rate of development Citation: Meshkova, V. Proc and cons of Climate Change for Forest Phytophagous insects, in Proceed- ings of the 1st International Elec- tronic Conference on Entomology, 1–15 July 2021, MDPI: Basel, Swit- zerland, doi:10.3390/IECE-10373 Published: 30 June 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and insti- tutional affiliations. Copyright: © 2021 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses /by/4.0/).