Federal inspectors in Halifax say they are searching two to three ships per week for signs of infestation of the Asian Gypsy Moth.
It's a subspecies of moth that could cause serious damage to Maritime forests.
The vessel inspections can only be done off the coast of Nova Scotia, meaning some ships headed for Saint John have had to be diverted off course.
The Canadian Food Inspection Agency in Halifax says it has conducted 80 searches this year on vessels coming into Canadian waters after spending time at high-risk ports in Japan, Korea, China and Russia.
They recently boarded an LNG supertanker headed for Saint John, according to Inspection Manager Scott Bishop.
He said the Mekaines had to take a detour to Chebucto Head.
"They were coming from Europe. So they would have been stopped before they came into the Bay of Fundy," Bishop said.
The agency says it has intercepted an alarming number of egg nests on vessels on the Pacific Coast.
So far, searches for nests on the Atlantic Coast have not turned up anything.
Forestry researcher David Gray says if the insects showed up here, it could be disastrous.
"Because the Asian strain has a much wider range of host range, which means it will feed on many more species than does the North American strain, it poses a concern to rural forests, to urban forests, it poses a concern to rural forests, to urban forests, to streetscapes, to nurseries, to orchards," Gray said.
"So it is a concern. We'd like to keep it out as long as possible."
So far this year, four oil tankers headed for New Brunswick have been inspected.