The discovery of insects on board the containership, Coral Islander, resulted in the freighter being asked to leave American Samoa, a few hours after it arrived over the weekend.
The vessel has been sent back to Fiji to be fumigated.
The Director of Agriculture Apefai Taifane says the decision to send the vessel back was made to safeguard the territory from unwanted pests.
Polynesian Shipping, agents for the Coral Islander, say the mystery insects were discovered during unloading operations.
It says samples of the bugs have been sent to New Zealand for testing.
The vessel came from Fiji and Samoa.