What causes twig dieback from periodical cicadas?

Twig dieback caused by periodical cicadas is primarily a result of ovipositing, or egg-laying. Female cicadas create slits in plant twigs to deposit their eggs. This process leaves the plant tissue damaged, leading to an interruption in the flow of nutrients and water. After the eggs hatch, the twigs can no longer support the plant adequately, resulting in dieback.

Although the adults may feed on foliage, this is generally not the primary cause of dieback; their feeding tends to be less damaging compared to the impact of the egg-laying process. Likewise, while larvae do feed on roots, this is typically not associated with twig dieback as directly as the damage from ovipositing. Feeding-induced galls can impact overall plant health but are not directly responsible for twig dieback in the same way that ovipositing is. Thus, the mechanical injury to the twigs from the female cicada's egg-laying is recognized as the main contributor to this phenomenon.