ISA Certified Arborist Practice Exam

Weak or stressed trees are more likely to be susceptible to bark beetle infestations because these trees are already under duress, making them less capable of producing the natural defenses that healthy trees utilize. When a tree is stressed due to factors such as drought, injury, disease, or competition for resources, its ability to produce resin—which serves as a defense mechanism against bark beetles—is diminished. Bark beetles are attracted to trees that are weakened and may also have a higher likelihood of colonizing these trees because they are unable to effectively resist the beetles' attacks.

Healthy trees generally have stronger defenses and can often repel insect infestations more effectively. Young trees, while they may face unique growth challenges, are not inherently more susceptible to bark beetles than stressed trees. Fast-growing trees can sometimes fend off pests better due to their vigorous growth, provided they are healthy. Thus, the condition of the tree plays a critical role in its vulnerability to beetle infestations, with stressed trees standing out as the most at risk.