Agricultura tropica et subtropica, Universitas Agriculturae Praga, Vol. 34, 2001: 101-109











The discovery of the screwworm Cochliomyia hominivorax in Libya in 1988 represented an emergency for the surrounding regions. Classical treating diseased animals and preventive spraying by insecticides proved to be not in the position to block screwworm spreading and eradicate it. Decision was made to use sterile insect technique. Irradiated sterile flies were airlifted from Mexico factory. There were dispersed aerially about 1260 million flies covering 25000 km2 of invaded territories and 15000 km2 of protective barrier zones. This method requiring long demanding preparation and solving immense problems of biological, managerial, financial and social character conduced to eradication in less than one year. Afterward North Africa as well as Eastern Hemisphere could be declared to be again free of this myiasis. Pre-eradication programme cost about 10 million US$ and the eradication 80 million US$. Benefit-cost ratio was very high.


Key words: Cochliomyia hominivorax - screwworm  - disease control - disease eradication - sterile insect technique.


List of abbreviations: NWS - New World Screwworm (Cochliomyia hominivorax); SECNA - FAO Screwworm Emergency Centre for North Africa; STI - Sterile Insect Technique






The discovery of the screwworm Cochliomyia hominivorax Coquerel) in Libya in 1988 represented an emergency for the entire North African region. There was a disastrous potential for the NWS to spread into other countries of the North Africa region and then into the Near East and Europe. Confirmation of the NWS by the FAO mission started international emergency and eradication activities. Initial control methods based upon classical procedures through treating diseased animals and preventive spraying by insecticides proved to be not in the position to block screwworm spreading and to eradicate it.


The first mission sent by FAO in April 1989  recommended using sterile insect technique of Bushland and Knipling (1938). The screwworm flies are reared artificially and exposed to irradiation by caesium 137 shortly before they emerge from the pupae. Male flies are sterile but able to mate. The female mates only once, and when mated with a sterile male, lays eggs that do not hatch. Therefore, release of sufficient numbers of sterile males in an area over a period of time leads to eradication. This programme along with the use of insecticides that killed adults, led to eradication of screwworm in USA and Mexico. The success of SIT depended on the ability of the factory-reared sterile males to compete with wild males and mate with a sufficient percentage of the wild female population to break the wild pest's life cycle.






Material and Methods


The paper is based upon personal experience (1), publications of Abusowa (3), Reichard (2), Lindquist(3) and Vargas-Teran (4). Other sources represented publications of the FAO (5,6) and documents of FAO Screwworm Campaign Action Group, FAO/IFAD Screwworm Campaign Action Group and FAO Animal Health Service Screwworm Task Force, all chaired by the author of this article as the Chief, Animal Health Service, FAO.


 To apply the STI for NWS eradication in North Africa there were elaborated and used particular methods for:


- identifying programme phases and key moments for STI application in time and space based upon epizootiological analyses;


- comparing North African strain how far was compatible with the strain used for mass production of sterile insect in only factory in the world located in Tuxtla Gutierrez in Mexico;


- sterile screwworm surviving in the best possible conditions from the factory up to final dispersion and mating in target zones in a very distant territory;


- transcontinental transport of sterile flies and their storing under North African conditions up to reach the optimal stage for release and mating;


- effective system of aerial dispersion of sterile flies in terms of frequency, intervals, size and location paths;


- continuous control from production factory up to effectiveness of STI practical application;


- continuous surveillance in invaded and threatened zones and countries.






 Preventive (containment) phase


This phase consisted in: establishment of specific diagnostic system to detect and monitor NWS in the North Africa region; controlling live animal movement (individually examined for wounds and screwworm larvae) to prevent introduction of NWS to territories free of the pest; reporting on the worldwide situation of infested and NWS-free countries and on risks involved in international trade; improvement of methods for rapid and economical deployment of the STI.


One of the first action was to arrange for production of coumaphos (5%) powder for treatment of wounds and prophylactic spraying (0.25%) as well as to reorganize inspection activities within 21 days (the average life cycle of the NWS).  Millions of sampling/treatment kits which consisted of a small amount of insecticide powder and larval collection tubes were routinely provided to livestock owners.


In December 1989, tests confirmed that Mexican and Libyan NWS strain were compatible. Then, it was necessary to determine how the pupae would be transported to Libya and then dispersed over the infested zone.


After not easy legislation process, on March 15, 1990, United States President Bush signed law permitting the sale of sterile NWS produced under US and Mexican governments to be used in Libya. Very complicated negotiations for contract agreements suitable to all parties including international organizations and many other countries, took five months.


Sentinel pens with surgically wounded sheep were established and wind-oriented traps baited with the NWS fly attractant (swormlure-4) were set up to gather live NWS to test suitability for STI under North Africa conditions. There were established fixed and mobile quarantine stations.


Sterile flies production capacity of the Mexican facility was significantly increased to be able to meet additional requirements for eradication programme in North Africa. Necessary support in terms of staff, funds, organization, management, equipment, transport, facilities, logistic, communication, extension, etc. was ensured.



Pilot phase


This phase was necessary to develop the infrastructure and test the feasibility of transferring the proven technology, i.e. to test the logistic support necessary to apply SIT successfully in North Africa. Laboratory facilities were established for identification of NWS and quality control. The tests involved analyzing emergence, mortality, flight agility and longevity and were conducted both in Libya and Mexico.


The sterile NWS is a living insect and requires particular conditions with regard to temperature, packaging, shipping, storage, handling and must be transported within a limited period. In order to ensure good quality flies, a decision was taken to transport the insect in the pupal stage by packing 1600 pupae into small biodegradable cardboard dispersal boxes. Each box contained a small cup of special gelled diet for the emerged flies. The temperature during ground and aerial transportation of the pupae must remain at 10oC. The pupae were transported in refrigerated trailers from the factory to Mexico City (20-26 hours) and then by commercial airline in special containers to Frankfurt, Germany (12-15 hours) and then by charter flight to Tripoli (3-4 hours). Here the sterile flies were stored in chambers at a temperature of 25oC to 27oC for a minimum of 48 hours until 80 % of the pupae emerged.


Then the boxes were loaded on twin-engine aircraft, each fitted with a specially designed chute through which the boxes were released at a predeterminated rate. The boxes were designed to open during their fall from the aircraft, or on impact with the ground, thus releasing the flies.


In December 1990 started dispersion with more than 5 million of sterile flies. Pilot dispersion continued in January 1991 into eradication phase without interruption.


The dispersal aircraft flew along predetermined paths, 4 km apart, and boxes were dispersed at a rate of 3 to 10 per minute as the plan flew at 240 km/hour at a altitude of 500 m. On each dispersal day an area of approximately 6400 km2 was covered, with an average distribution of 800 flies per km2.



Eradication phase


The main activity consisted in intensive dispersion of sterile flies over infested area of about 25000 km2 and protective barrier of 15000 km2 including 2500 km2 in northeastern Tunisia. From January to 15 October 1991 a total 1257 million sterile flies were dispersed. Usual weekly dispersion of 40 million flies was carried out using five twin engine aircraft.


Activity of sterile flies and the ration of sterile to fertile flies in each area were monitored. Laboratory tests were targeted to pupal weight, emergence, malformed pupae/adults, sex ratio, longevity without food and water, longevity with food and water, sterility, Tripoli longevity, mortality, flight agility, etc. Special study was carried out about emergence upon arrival, temperature strategy, bag test, chilling of emerged flies, prolonged chilling of boxed pupae, heat stress, hypoxia and release/capture study to determine dispersal and longevity of sterile NWS flies (ground releases were made of sterile flies marked with a fluorescent dye).


Effective international technical and financial assistance together with strong national public veterinary service were considered the crucial pre-requisites for success. The government provided a range of facilities, support staff and other assistance to the project.  Department of Veterinary Service employed approximately 300 veterinarians and supporting staff of about 1200 persons. In total more than 50 million inspections were recorded (e.g., during eradication phase - every months the surveillance units were carrying out about 3 million inspections and treating nearly 20000 wounds). National authorities ensured also: landing, take-off, parking, servicing, refuelling and repair facilities for project aircraft; facilities for unloading, storage and loading of boxed flies; flight control through aeronautic maps and ground-to-air communications; access to national and international communication facilities for project staff; ground support staff to assist with air dispersal and biological and veterinary monitoring; sentinel animals for biological assessment; office, laboratory and storage facilities for diagnosis and identification. Particular role had specialists with experience from screwworm eradication in USA and Mexico.


Because no further evidence of NWS in the six months following detection of the last case in April 1991 (Tab. 1), SIT activities were terminated.



Posteradication phase


The continuous compilation of NWS negative results of surveillance throughout the country confirmed the evidence that NWS no longer exists in North Africa. A resume of data from field activities since beginning of May 1991, the first month with no NWS detected, through to the end of the year shows that nearly 100 000 trapped females NWS flies were dissected, with no fertile flies found. The number of inspections of animals exceeded 22 million, with 700 samples of other larvae collected from wounds, but no NWS found. Almost 3/4 million animals were inspected at quarantine stations, with the same results. Continuous surveillance in following years confirmed NWS eradication in Eastern Hemisphere.




Discussion and conclusion


The fly's mobility makes containment extremely difficult. Adult flies can travel up to 200 km and, where conditions are favourable, the size and range of the population can expand rapidly. The screwworm presence in Libya, therefore, was a concern of international significance: unless quickly eradicated, it would inevitably spread. It could easily migrate around North- and West African coasts and down the Nile valley. Such as infestation would be virtually impossible to eradicate and the countries affected would be saddled with the on-going expense of treatment and control programmes and with incalculable losses in livestock production and sanitary consequences. The only way to prevent this devastating insect pest from spreading throughout the Eastern Hemisphere was through immediate eradication ("now or never!").


 In addition to the economic impact, a continent-wide infestation would pose a major human health risk. In remote areas where medical facilities are limited, human would fall easy victims - particularly children, the sick and the aged. For Africa's wildlife was the risk of reducing natural populations and establish a permanent "breeding pool" from which it could re-infest domestic herds.


 Eradication was achieved in very short period before the parasite spread and become enzootic in the Mediterranean Basin and eventually other areas of Eastern Hemisphere which could be declared to be again NWS free.


 For the pre-STI programme were allocated 10.6 million US$ (Tab.2) and cost of the eradication achieved about 80 million US$ (Tab.3). The eradication had shown a clear economic return. Independent study, considering also avoiding future spreading, showed a benefit/cost ratio for the whole region of 50:1 (6).


 The responsibility for the programme preparation, management and coordination of antiscrewworm action was with above mentioned FAO Screwworm Campaign Action Group (from 27 April 1989), later changed into FAO/IFAD Screwworm Campaign Action Group and FAO Animal Health Service Screwworm Task Force. From July 1990 the responsibility took over SECNA with special staff and financing.


 Some fortunate features should be mentioned: The outbreak occurred in a fertile oasis area surrounded by desert and the Mediterranean sea, in a country with sufficient veterinary service resources and willingness to apply control measures.  Intensive and continuous public information campaign encouraging animal owners to try to prevent wounding, where wounds were found to treat them and simultaneously collect samples of any fly larvae present.


 Success of NWS programme provided useful precedence: rapid recognition of the problem, determination of its extent, early development of a sound technical programme of action, establishment of a single executive unit with necessary funds and authority to implement the programme, clear delineation of the responsibility of different agencies involved and implementation of an extensive communication campaign to ensure that people in the affected regions are fully informed on the programme (using radio, TV, leaflets, posters, etc.). The population was informed why low-flying aeroplanes would be dropping cardboxes full of foreign flies over large sections of the country (before 1989 NWS was known as American screwworm).


 If the NWS infestation had spread into other areas of Africa it would quickly have become a major threat to livestock, wildlife and even human health. The continent would have been faced with livestock losses amounting to thousands of millions of dollars and on-going treatment and control costs of hundreds of millions more.


 Africa was been saved from the devastating impact of a permanent infestation. This eradication belongs among the most effective programmes in controlling animal and human diseases.






1.      Kouba, V., 1990. Information note on FAO activities to combat screwworm in the Near East Region. 20th FAO Regional Conference for the Near East, Tunisia, 7 pp.

2.      Reichard R., 1999. Case studies of emergency management of screwworm.,1999,18(1): 145-163.

3.      Lindquist D., Abusowa M., 1991. The New World screwworm in North Africa. FAO Wld. Anim. Rev., Spec. Issue: October, 2-7.

4.      Vargas-Teran M., 1991. The New World screwworm in Mexico and Central America. FAO Wld. Anim. Rev., Spec. Issue: 28-35.

5.      Food and Agriculture Organization of the United Nations, 1989. Manual for the Control of Screwworm Fly Cochliomyia hominivorax, Copquerel, 93 pp.

6.      Food and Agriculture Organization of the United Nations, 1994. The New World screwworm eradication programme: North Africa 1988-1992. 192 pp.




Author´s  address:

Prof.MVDr. KOUBA Václav, DrSc.

P.O.Box 516

170 00  Praha 7

Czech Republic

Larvae collected from wounds in Libya from 1989 to 1991


Year       Total      Screwworm larvae    Percentage positive


1989       5805               1938                  33 %

1990     12557            12068                   96 %

1991      1090                     6                    0.5 %


Total    19452            14012                  72 %



Tab. 2

Allocation of funds for the preventive (containment) phase (in US $)


Personnel                                               405 000

Equipment and supplies                       1 105 918

Purchase of flies                                     157 843

Transport of flies                                    664 674

Dispersal of flies                                     138 965

General operating expenses and

          direct operating expenses             137 965

Libya contribution                                7 500 000

IAEA contribution                                  507 000


Total                                                10 617 365



Tab. 3

Eradication programme breakdown of overall funding sources (in US$)


Initial phase (FAO, Libya, UNDP)                                             3 700 000

Pilot phase (FAO, Libya, IFAD, AfDB, UNDP, IAEA)           10 700 000

Eradication programme                                                            60 600 000

  multidonor funds                                                                    32 600 000

  Libyan contribution (cash)                                                      11 400 000

  Libyan contribution (in kind)                                                   14 600 000

  Neighbouring countries (in kind)                                               2 000 000

Bilateral donations to Libya and

  neighbouring countries                                                              5 100 000


Total                                                                                       80 100 000