Answer:
a mouthpart that can pierce fruits and seeds
Step-by-step explanation:
An adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms. That being said the most likely morphological change that would trigger this would be a mouthpart that can pierce fruits and seeds. This new change would allow the beetles to consume most of the different resources that the island has to offer such as the different types of plants and fruits which were previously inaccessible to the beetles.