It took the death of a tree at Moanalua Gardens last year for the alarm to be sounded.
A tiny red bug called the Lobate Lac Scale took down the great banyan.
That was the threat at the time-- a single bug.
"They are kind of like vampires. They will suck the life out of the trees,” said city urban forestry administrator Stanly Oka.
But now two other pests have surfaced: a gall wasp that attacks leaves and another that attacks twigs.
The city now says close to 400 Chinese and Ficus Benjamina Banyan trees are under assault. That number does not include trees on state land or private property.
Oka said it is the worst he has seen in his 35 years on the job.
And he worries the situation could get worse this summer.
”If we don’t have some kind of relief soon, I am really concerned about the rest of the banyans we have," Oka said.
The city discovered at least 40 diseased trees at Ala Moana Beach Park--some of them on the exceptional tree list.
“We have to watch those trees and see what we can treat, and see what we can save," Oka said.
The city plans to remove two diseased trees at Thomas Square this week. There are another five in Waikiki on Monsarrat Avenue, and there are more along the Ala Wai Boulevard.
Fortunately so far, the insects have not attacked the historic Indian banyans with the massive aerial roots that surround around the Thomas Square fountain.
Nor have they targeted the city’s monkey pod trees.
The Outdoor Circle has applauded the city's efforts to try and save the banyans by injecting insecticide in holes drilled in their trunk.
It is the only weapon that arborists have to combat the insects which have attacked young and old trees.
The city has been able to save some trees, but not others.
"So it’s really hard for us to keep on top of, and it seems as every time we turn in a different direction we see more," said Oka.
"The possibility of it spreading is quite high and it's just a matter of time before it spreads through the urban forest in Honolulu and all the islands,” said the Outdoor Circle’s Marti Townsend.
One of three very old banyan trees at the Catholic Cemetary on King Street may have to be removed. The church says an arborist is recommending it be taken down since it is also threatening a historic incinerator.
Just last week Trees of Hawaii removed a similar diseased Banyan at Washington Place.
"It breaks your heart because there nothing that you can do to save them," said Abner Undan of Trees of Hawaii who would prefer to save trees, not cut them down.
“People need to be prepared with all of these infestations, banyans may be a rare sight in Hawaii in the near future," warned Townsend.
The city hopes to send someone to a conference in California to learn more about possible new strategies to save the large canopy trees.
The Lobate Lac Scale insect has been known to attack many species of trees.
If you have a tree in your yard you are worried about, you should contact a certified arborist.