Screwworm Flies

Photo Credit: Screwworm Commission The New World Screwworm (Cochliomyia hominivorax) (NWS) and the Old World Screwworm Chrysomya bezziana (OWS) are major parasitic insect pests are destructive and often fatal pests of all warm-blooded animals, including humans. Females lay eggs into animal wounds and on soft tissues such as the nose, navel and anus. The larvae burrow through the flesh creating bacterial infections that attract more egg-laying females.

The disease is called myiasis, and the magnitude of the problem dictates that its control be a prerequisite to the maintenance of a viable livestock industry and the increasing need for agricultural production.

The world organization for animal health, Office International des Epizooties (OIE), classifies NWS and OWS caused-myasis as a List B disease - a transmissible disease which is considered to be of socioeconomic and/or public health importance within countries and which is significant in the international trade of animals and animal products.

The NWS was once endemic throughout the Western Hemisphere, but has been eradicated from the USA, Mexico and Central America and Panama, using AW-IPM approach using the SIT. A permanent barrier of sterile insects is maintained over eastern Panama to protect the NWS-free areas. Campaigns to eliminate the pest from the Caribbean continue. In 1988 the pest was found in Lybia and an urgent national and international effort was mounted integrating the SIT to prevent its spread to livestock and wildlife in the rest of Africa and the Mediterranean Basin. The campaign was successful in achieving eradication, preventing the enormous losses, which would have occurred if the infestation had spread and become permanently established.

Research into NWS has been underway for over 50 years, mostly by USDA, and there is an extensive literature for this species. Screwworm research may become even more important in the future in order to reduce programme costs or if the NWS eradication efforts are expanded to include South America.

The OWS is endemic to Africa, and South Asia. In addition, over the last decades it has invaded the Persian Gulf region including Iraq. OWS is not present in Australia but is considered to be a major threat to livestock and native fauna owing to its presence in Papua New Guinea and Indonesia. A major element of Australia's long term screwworm fly preparedness is to validate the SIT for OWS. Compared to NWS, comparatively little research has been undertaken into OWS. Most of it was undertaken by Australia in Papua New Guinea and more recently in Malaysia.