Retired Navy Capt. John D. DeCoursey, 73, an entomologist in the naval medical service for almost 30 years, died of heart and lung failure Tuesday at Bethesda Naval Medical Center.

Capt. DeCoursey studied the medical aspects of diseases borne by insects and discriminated information about them.In 1962, he founded the Military Entomology Information Service at the Walter Reed Army Medical Center annex in Forest Glen. He received a Defense Department commendation for this work.

He had a special interest in mosquitoes, which carry malaria. He began his naval career in 1942 during World War II and was assigned as a malaria control officer in the Paname Canal Zone. He later had similar responsibilities on Okinawa in the Pacific.

Capt. DeCoursey was stationed at the Navy's bureau of medicine and surgery in Washington from 1945 to 1950, and then spent four years at Camp LeJeune, N.C. From 1954 to 1956, he was stationed in Cairo, Egypt, and then returned to the Washington area for the remainder of his career. He retired in 1970.

Capt. DeCoursey was born in Indianapolis, Ind. He earned a bachelor's degree at Louisiana State University and master's and doctoral degrees in medical entomology at the University of Illinois. He worked for the U.S. Department of Agriculture in Idaho and at the Agricultural Research Station in Beltsville, before beginning his naval service.

He was a member of the American Mosquito Control Association.

Survivors include his wife, Anna M., of the home in Bethesda; a son, Donald W., of Unionville, Va.; a daughter, Patricia Ann Woosley, of Decorah, Iowa; a brother, R. M. DeCoursey, of Storrs, Conn., and two grandchildren.