MEXICO CITY (AP) – Two Guatemalan pilots and a Mexican agronomist engineer died June 6 when their plane crashed in southern Mexico near the border with Guatemala as they freed sterile flies meant to stop the spread of screwworm in cattle.

Mexico’s Agriculture Ministry said in a statement that the Guatemalan plane crashed near Tapachula in southern Mexico, but did not give a cause.

Mexico had stepped up efforts to control the spread of the pest last month under pressure from the United States government, which suspended cattle imports from Mexico because of fear of the screwworm.

President Claudia Sheinbaum had said that she didn’t know when the suspension would be lifted, but that specialists from the U.S. were in Mexico studying the country’s efforts.

The screwworm is a larva of the Cochliomyia hominivorax fly that can invade the tissues of any warm-blooded animal, including humans. The parasite enters animals’ skin, causing severe damage and lesions that can be fatal.