Despite efforts to minimize the damage it causes, an invasive insect is continuing to spread throughout the state, killing ash trees.

This week, the Minnesota Department of Agriculture found more emerald ash borer beetles in trees around the University of Minnesota area.

The green-shelled beetle originated in Asia and was first found in North America in 2002. Its larvae destroy the tree’s ability to transport water and nutrients, which can kill the tree within two years of symptoms surfacing.

Minnesota has the largest population of ash trees in the nation –– just shy of a billion, according to the MDA. The insect has killed tens of millions of trees in 15 states since its introduction into the environment.

Since November, the MDA has been collecting ash tree branches in Minneapolis, St. Paul, Lauderdale, Roseville and Falcon Heights. So far, 275 out of 600 branches, taken from 300 trees, have been sampled for EAB presence, according to Jonathan Osthus of the MDA’s Plant Protection Division.

The sampling process includes peeling back part of a branch, inspecting for S-shaped galleries.

Fifteen trees were found to be infested, at least seven of which are in University-area neighborhoods.

Two years ago, the MDA gave the University $200,000 to remove infested trees on its campus. The school removed 650 trees, said Les Potts, grounds superintendent.

Potts said he plans on removing more trees but that right now the effort has been “scaled back.”

Meanwhile, the city of Minneapolis is preparing to fight what Ralph Sievert, director of park forestry at the Minneapolis Park and Recreation Board, calls “the anticipated population explosion of emerald ash borer.”

 “We’ve been trying to remove what we call defective and declining trees,” he said.

Sievert said the city is removing ash trees from the area even if they are not infested with EAB but merely damaged. Since infestation is seen as inevitable, the city is removing trees likely to get infested now to minimize impact later, he said.

“Any excuse that we’ve got to remove an ash tree now — we’ll use it,” Sievert said.

In 2010 the city received a grant from the MDA, which helped fund the removal of 1,410 trees. In 2011 it removed 818.

Sievert said the city will replace any boulevard trees residing on residents’ properties for free.

“It’s your tax dollars hard at work,” he said.

To prevent the spread of the EAB, the MDA outlawed the transportation of any wood out of quarantined areas in the state.

The trees the city removes are chipped into tiny wood pieces and given to nurseries to use as a potting soil medium.

The chipping will eradicate any EAB within the wood, making it safe for transportation.

Any person found transporting contaminated wood could face civil penalties up to $7,500.