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Have you ever noticed tiny bumps on the branches of a tree? These may have been scale insects. These small insects feed on tree sap. Scale insects on urban trees are notably more abundant than those on rural trees. As a result, urban trees suffer from heavy infestations, and are often unhealthy or die. To protect and restore urban tree health, we needed to determine the factors that make these tree pests more successful in urban habitats.

Living organisms interact closely with each other and their environment. For this reason, we investigated the combined effects of urban warming and drought on trees and their insect pests. We measured drought stress in trees, counted the number of insects on each tree, the embryos developing inside female insects, and measured their body sizes.

The warmer, more drought-stressed trees harbored more successful pests than cooler, less drought-stressed trees. Our data suggest that as cities and natural habitats become hotter and drier, damaging scale insects will become more abundant.

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