Troubled Flies (IMAGE) University of Iowa Caption Green spaces in cities are great, but they don't ensure biodiversity, according to University of Iowa biologists. The team found insect abundance was lacking in two common urban trees, suggesting insect movement, such as the walnut fly, pictured above, may be limited by barriers, such as roads and buildings. Credit Andrew Forbes lab, University of Iowa Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.