BASF said it sued two smaller rivals on Thursday for infringing on patents for an insecticide that forms a core part of the company's North American crop protection business.

BASF said the lawsuits accuse Israel-based Makhteshim Agan's North American subsidiary and privately held Cheminova of preparing to sell generic versions of fipronil, an insecticide marketed as Termidor. Nevin McDougall, vice president of BASF's crop protection business, said in an interview that BASF discovered the companies were preparing to market the product through regulatory filings and when the companies informed BASF.

The lawsuit, filed in U.S. District Court in North Carolina, demands the companies give up plans to market generic versions of the product. The product patent for the fipronil chemical expires in August. However, BASF said it has another set of patents related to the manufacturing process that would prevent a rival from marketing any generic versions.

"Clearly, there's a violation of our intellectual property," McDougall told Reuters. He declined to comment on whether the lawsuit seeks monetary damages, and would not provide exact sales figures for fipronil. But McDougall said BASF has about 25-30% of the North American insecticide market. Representatives from Makhteshim were not available for comment.

Martin Petersen, chief executive of Denmark-based Cheminova's North American operations, said his company had done no wrong.

"Cheminova does take patent rights very seriously," he told Reuters. "We are confident that we are not in any imminent infringement of any patent rights affiliated with this insecticide."

Fipronil is primarily used to combat termite infestation in wood-framed homes, and works much like home ant bait kits.

"The primary method of application ... essentially forms a barrier around the homeowner's structure," McDougall said. "As the termites approach the structure to chew on the dwelling, it essentially ingests the active ingredient, takes it back to the colony and destroys the colony."

Fipronil is also used to control insects that attack potato crops. It is part of BASF's broader global crop protection business, which brought in 2009 revenue of about €3.3 billion. BASF said that Bayer CropScience had joined BASF in the lawsuits. Bayer kept some patent rights to fipronil after BASF bought the business in 2003.