Final answer:
The emerald ash borer is the leading insect threat to trees in Oklahoma cities, causing significant damage to ash trees. Climate change has allowed invasive species such as this beetle to thrive, leading to the deterioration of forests and creating complex ecological challenges.
Step-by-step explanation:
The insect that currently poses the biggest threat to trees within Oklahoma cities is the emerald ash borer (Agrilus planipennis). This invasive beetle has caused significant damage to American ash trees across the Midwest to the Mid-Atlantic States. As a result of climate change, with milder winters and longer summers, the emerald ash borer is able to overwinter in greater numbers and has a prolonged season to inflict damage on ash trees. This has led to major mortality among these trees, and therefore, a serious environmental concern.
Additionally, climate change has been tipping the balance in favor of native pine bark beetles in North America and Europe. These beetles are now able to survive through milder winters and reproduce additional generations in the extended summer seasons, resulting in the death of up to 70% of trees in some forest areas. With such high mortality rates, forests face a compounded forest management and fire management problem. Moreover, other invasive species, such as the Asian balsam woolly adelgid and hemlock woolly adelgid, are exacerbating the threats to forests in the United States.
It is important to note the role of certain biological control methods, such as the use of a pathogenic fungus, Beauveria bassiana, which can potentially act as a biological insecticide against the emerald ash borer. Nonetheless, the overall impact of invasive insects on urban and natural forests remains a deeply concerning issue, with the need for effective management strategies to mitigate the damage and protect tree populations from these pests.