Did the sterile insect technique or weather eradicate screwworms (Diptera: Calliphoridae) from Libya?

The American screwworm, Cochliomyia hominivorax Coquerel, was detected in northwestern Libya in 1988. By August 1990, a screwworm epizootic extended over 26,000 km2 but collapsed in December and disappeared in April 1991. The relative contributions of winter weather and sterile insect releases on screwworm eradication in Libya were assessed by using temperature data and population demography. A screwworm overwintering threshold mean temperature of approximately 9.7 degrees C for 3 mo is supported strongly by published experimental and epizootiological data. In Libya, temperatures were above this overwintering threshold at Zawia, Sorman, and Tripoli weather stations. At Gharyan, in the interior highlands, mean winter temperatures from 1 December 1990 to 28 February 1991 were less than the putative overwintering threshold. No kill of screwworm pupae or adults was likely as a result of low temperatures near any weather station in the winter of 1990-1991. Evidence of screwworm overwintering in 1990-1991 was provided by the detection of a natural infestation in April and trap captures of numerous wild adult females in February, March, and April. Successful screwworm overwintering was highly probable in the coastal plain of Libya but unlikely in much of the interior highlands. The high rate of animal inspections by eradication personnel achieved as much as a 30% chance of detecting a screwworm case in domestic animals. Generation times and expectation of life among feral adult flies were estimated. Case reports for January to June 1991 were consistently less than estimates based on historical experience in Libya 1989-1990 and in Texas 1962-1983. Phenological simulations of sterile mating rates in feral screwworm flies supports the contention that sterile fly releases led to a greatly reduced case incidence from January to the time that eradication was declared in October 1991.