Effects of temperature and habitat complexity on an urban tree pest (Tinocallis kahawaluokalani), natural enemies, and predation services in the city

Trees provide many ecosystem services in our urban environments. However, city trees are often stressed by pests and hot urban temperatures. Our research highlights how temperature affects a common tree pest, crape myrtle aphid (Tinocallis kahawaluokalani), natural enemies, and egg predation services on crape myrtles in the city. This research addresses an area of study that has largely been unexplored, effects of temperature on urban natural enemies, and it sheds light on how hot urban temperatures affect one species of piercing-sucking herbivore, a guild that is generally thought to be benefitted in hot city environments. To test our hypothesis that temperature increases T. kahawaluokalani density, fecundity and population growth, yet decreases natural enemy density and egg predation services on street trees, we collected data on crape myrtle trees in Raleigh, NC and conducted lab experiments in 2018. We collected canopy temperature and arthropod data on study trees from May–August and measured local structural complexity around trees and plant water potential. Aphid density decreased with hotter urban temperatures. However, natural enemies and egg predation were not affected by temperature. Natural enemy density was most correlated with local structural complexity. Together these findings suggest that increasing local structural complexity around trees may be a way to support natural enemies on both cool and hot urban trees. Our findings also emphasize the need for similar studies that evaluate temperature effects on common tree pests to help landscape managers prioritize pest targets for pest control in a warmer and more urban world.