It now covered close to 50,000 hectares of the central northern plateau, including one-third of Tongariro National Park.
Dr Fowler said the Department of Conservation and the Army had been unhappy about the spread of the heather. It posed a fire risk, grew big and dense, getting in the way of military exercises and was harming native plant habitats.
The Army had planned to spend a large amount on herbicide to clear the heather but it would have also harmed native vegetation.
The beetles by comparison were selective, with trials showing they ignored other plants, just focusing on the heather.
Dr Fowler said it took a number of releases of the beetle, going back to 1996, before it gained a stronghold and finally started showing its impact this summer.
Some of the beetles initially brought in from Britain had a gut parasite so had to be destroyed in quarantine, but after many attempts at colonisation about 250 from Yorkshire became established near the Desert Rd. In the 2006-2007 year only 0.2ha of the heather was eaten but there had since been a 10-fold increase in its destruction, with 2ha wiped out this year.
"The beetle is just beginning to show what it is capable of."
About half of the destroyed heather was in a patch on the eastern side of the Desert Rd and the rest on a frost flat, an uncommon type of habitat home to distinctive indigenous flora, northwest of the national park.
Dr Fowler said probably more than a million beetles were established on the plateau. They had proved they were capable of impressive damage and although they would not entirely eliminate the heather they would keep it well under control.
The beetles had caused major problems in Scotland and European heathlands, where heather was valued.
Massive outbreaks of the voracious insect occurred about every 10 years.
