The Northern Marianas' Department of Land and Natural Resources has found the destructive coconut rhinoceros beetle on Rota.
The invasive pest is a major threat to several palm species.
Our correspondent said 20 adult beetles and many grubs were found when a coconut tree fell down.
The presence of the beetle in neighbouring Guam had been known for the past ten years but the CNMI was thought to be free of it.
The department said trapping is needed to find out how bad the infestation is.
It also plans to conduct an island-wide visual survey for signs of the beetle's presence and says it will start a clean up, working out from the discovery site.