PORTLAND – The former Peoples Heritage Financial Group said Monday its second-quarter net income grew 200 percent compared with the same period last year when it acquired Vermont-based Banknorth Corp.

The big jump was caused by special charges taken by Peoples Heritage during the merger in which its name was changed to Banknorth Group Inc.

On an operating basis, which excludes special charges, earnings for the latest quarter were up 8 percent, the company said.

For the three months ended June 30, net earnings were $59.9 million, or 43 cents per diluted share. That compared with $18.9 million, or 13 cents per share, in the same period last year during the merger.

Strong commercial lending and increased insurance commissions and demand deposits were behind the growth, said William J. Ryan, chairman, president and chief executive officer of Banknorth Group.

Commercial loans have helped to generate a 15 percent increase in checking deposits, while insurance commissions have nearly doubled because of acquisitions and a strengthening of the market, he said.

The merger a year ago increased the bank holding company’s assets to $18.5 billion and expanded its banking operations from four states to six.

Banknorth’s subsidiary banks include Peoples Heritage Bank in Maine and Bank of New Hampshire, which have leading market shares in their respective states.