INCREASED EFFECTIVENESS AND APPLICABILITY OF THE STERILE INSECT TECHNIQUE THROUGH MALE-ONLY RELEASES FOR CONTROL OF MEDITERRANEAN FRUIT-FLIES DURING FRUITING SEASONS

One of the main obstacles for a wider use of the Sterile Insect Techni que (SIT) against the Mediterranean fruit fly (medfly) is the damage c ommercial fruit suffers due to sterile female stings. To overcome this obstacle, the Joint FAO/IAEA Division of Nuclear Techniques in Food a nd Agriculture has played a leading role in sponsoring and carrying ou t research to develop medfly genetic sexing strains that allow male-on ly SIT releases. Recently, as a result of this continued FAO/IAEA effo rt, genetic sexing strains based on a temperature sensitive lethal (ts l) mutation have been developed at the IAEA Laboratories at Seibersdor f. Unlike previous pupal color sexing strains, these 'second generatio n' sexing strains allow female killing at an early (embryonal) stage. In addition, they are essentially stable under mass rearing conditions . This represents an important breakthrough because both of these attr ibutes were considered indispensable for genetic sexing strains with a ny potential to replace conventional strains with both sexes in large scale sterile medfly production facilities. Besides the considerable s avings in the costs of release and field monitoring, genetic sexing st rains in field tests have shown severalfold increases in the effective ness of the SIT as compared with the standard strains involving males and females. When releasing both males and females, sterile males are apparently not used effectively, because they use their limited sperm mostly to mate with sterile females and because they do not disperse w idely in the presence of these females. When males only are released, however, they disperse much further in search of wild females and comp ete more intensely with wild males for wild females. As a result of th e availability of usable male-only strains, and the demonstration of t heir increased effectiveness, the applicability of the SIT against med fly has increased in two different ways. Highly developed commercial f ruit growing regions, that previously had excluded application of SIT because of the fruit damage due to sterile female stings, are now reco nsidering such free area/exclusion programs. More-importantly, sterile male releases can now also be used for routine control purposes, rath er than only for eradication programs, partially or fully replacing ch emical bait-sprays during the fruiting seasons.