Flies at the Service of the Economy

The Mexico-American Commission for the Eradication of the Screwworm is a bilateral agency created by the governments of Mexico and the United States to combat one of the pests with the greatest impact on the livestock industry. After years of research and with excellent results in Mexico, the Commission offers other countries, mainly in Latin America, its products and services: top-quality sterile flies and technical consultancy for screwworm eradication campaigns at national and regional levels.

An insect approximately 10 millimeters long can affect an entire industry and cause losses worth millions. It is the case of the larva of the fly Cochliomyia hominivorax, commonly known as the screwworm, which when it reaches plague proportions can become a serious economic and health problem. In 2002 alone, an outbreak of this parasite in South America caused losses of over 3.6 billion usd, without taking into account the public health problems it represented.

The response in combating this pest is a revolutionary technique that uses atomic energy. In the 30s, Drs. Raymond Bushland and Edward Knipling devised a process to sterilize the flies that produce the larva, by means of irradiation with Cesium 137. After many years of laboratory work, in the 60s the United States succeeded in eradicating the screwworm from its livestock industry by using this technique.

Since 1965 the governments of the United States and Mexico began working together to share actions against the disease. In 1972 the Mexico-American Commission for the Eradication of the Screwworm (Comisión México Americana para la Erradicación del Gusano Barrenador del Ganado, COMEXA) was established, with the aim of strengthening the biological barrier that was maintained on the border between the two countries and eradicating the infestation in Mexican territory.

“This set the pace for the construction of a larva-producing plant with the idea of irradiating them and leaving them sterile,” said the director of the Commission, Alejandro Parra Carretero.

Thus, in 1974 construction began on a sterile fly producing plant in the state of Chiapas, Mexico, a region that afforded the possibility of air and land communication, and also provided a good opportunity to broaden the scope of the program thanks to its border with Guatemala.

In 1991 Mexico was declared free of the screwworm and COMEXA began to work with other countries to eradicate the pest.

Small and Lethal
The screwworm is fond of warm blood. If an animal has a wound, however small, the fly lays its eggs there, which can only be removed with a scalpel, since it covers them with something rather like glue, leaving them well stuck. Each lay can be of 400 eggs and each female has the capacity to lay up to 2,800 eggs in its 31 days of life.

The eggs hatch in just 12 hours. Once the larvae come out, they feed on the animal’s blood and liquids, which can even die if not seen to in time. The disease can also affect humans, in fact the larva’s scientific name derived from cases that arose in humans.

The countries that have the plague cannot export their meat or their cattle, and must even sacrifice the affected population, causing economic losses worth millions.

Alejandro Parra lived the screwworm crisis in Mexico as a veterinarian. He recalls that after the sterile fly producing plant was built in Chiapas, the next step was to completely eliminate the pest. After Mexico, work was carried out in Central America: Guatemala and Belize in 1994; El Salvador and Honduras in 1995; Nicaragua in 1999, Costa Rica in 2000 and Panama in 2003.

Today, COMEXA has two sterile fly producing plants: one in Mexico and the other one in Panama. Mexico’s plant produces an average of 200 million sterile flies a week, but is capable of producing up to 500 million in case of an outbreak.

“We establish a biological control every week. This consists of scattering flies in the regions to keep them free. Panama also does it in its region neighboring on Colombia. They produce only for that. In case of an outbreak we send them sterile flies,” explains Parra.

Export Flies
Throughout its history, COMEXA has accumulated significant experience in international cooperation to eradicate the screwworm.

In 1988 an outbreak was detected in Lybia. Work was carried out on inspection, treatment of wounds, spraying of domestic animals and of approximately 2 million heads of livestock – mainly sheep. From February to October 1991, COMEXA actively participated in dealing with this alert: 50 flights were made, carrying over 1.3 billion sterile flies from Tuxtla Gutiérrez, Chiapas to Tripoli, Lybia.

Today, the majority of the countries of South America and the Caribbean –except for Chile, which has natural barriers– are facing a problem with the screwworm. The risk is even greater in the Caribbean, where COMEXA is exploring the possibility of sending sterile flies. “Cuba is a risk and a priority. We are looking at how to attack the and the costs it would generate,” states Alejandro Parra.

Recently, the plant in Mexico sent 200 million flies to Panama and Jamaica and plans to export sterile flies to South America in the short term, after a pilot test in Brazil and Uruguay supported by the Inter-American Development Bank (IDB) and the United Nations Food and Agriculture Organization (FAO). The sterile flies produced by COMEXA traveled from Mexico to the border between Uruguay (Artigas) and Brazil (Rio Grande do Sul), and were subsequently released from small Uruguayan Army planes. The test was a success and feasibility studies are currently under way to implement strategies to attack the pest in this part of South America.

In Cuba’s case, COMEXA will support institutions such as the International Atomic Energy Agency (IAEA) and FAO, the main promoters of a project to eradicate the screwworm in the Caribbean, for which purpose the Commission will send flies not only to Cuba, but also to the Dominican Republic, Haiti and Trinidad and Tobago, with the aim of extending the scope of the biological barrier in the region.

At the same time, COMEXA continues its research work on new mass production techniques and assesses products to be used in the screwworm’s diet, in order to reduce production costs while maintaining the quality of sterile flies. Likewise, it participates in monitoring the regions where the pest has been eradicated and remains alert to possible outbreaks of this small parasite only 10 millimeters long that is capable of damaging the economy of an entire country.