Entomological warfare includes both the use of insects (and other arthropods) as biological weapons. The more common use is the insects being used as the carrier for vector-borne diseases. There have been, however, suggestions and reports of direct use of the insects to produce harmful effects, particularly against agricultural targets.
During the American Civil War, the Confederacy alleged that the Unionon introduced the harlequin bug, Murgentia histrionica, into the South. "Tremendous crop damage resulted in the South because of this pest. This allegation was never proven and it now appears that the harlequin bug moved on its own into the South from Mexico. However, humans may have aided in the movement of this pest."  Modern experience with the challenges of producing, transporting and delivering large numbers of insects throw doubt on the allegation.
Second World War
The early Japanese biological warfare program at Unit 731 emphasized vector-borne diseases, including both free fleas and parachuted flea-infested rats to spread fleas containing Yersinia pestis, the pathogen of plague. While they later moved to the aerosol methods used by Britain, the Soviet Union, and United States, they did not abandon the approach.
Nazi Germany had much smaller research program than the other countries, but did explore "using insects such as the Colorado potato beetle to attack Allied potato crops. The Germans were accused of dropping cardboard boxes filled with Colorado potato beetles over England from 1941-1943. The containers were never recovered but abnormalities associated with the presence of the beetles prompted Sir Maurice Hankey, head of Britain's BW effort, to write a memo to Winston Churchill with his concerns."
Recent studies have examined terrorist use of entomological warfare, with one scenario being the simultaneous release of Aedes aegypti mosquitoes infected with yellow fever. Mosquito control, therefore, would be a needed first responder capability. 
In the 1950s and 1960s, military researchers tested uninfected A. aegypti mosquitoes over domestic U.S. areas and at sea, and found that both airdrops and point-source ground spraying were feasible:
- Operation Big Buzz: 1955, airdrop over Georgia
- Operation May Day: April-November 1956, ground release in urban Savannah, Georgia
- Operation Drop Kick:
- 1956, aircraft release over Avon Park Bombing Range, Florida.
- 1958 further tests at Avon Park, but from helicopters
- Project Bellwether-I: 52 field experiments between September 1 and October 9, 1959, using human volunteers for bite counting
- Magic Sword: May 1965, at sea near Baker Island, part of Project Shipboard Hazard and Defense (SHAD),
- R.K.D. Peterson (1990), The Role of Insects as Biological Weapons, University of Montana
- Walter J. Tabachnick (2008), Mosquito Control as a First Responder to Bioterrorism, Florida Entomological Research Laboratory, University of Florida
- Stephen M. Baptista. (2010), work in progress for the upcoming book Chicken-Powered Nuclear Bombs: Unconventional Uses for Animals in War and Espionage (1935-Present)