Molecular tools in the evaluation of SIT programmes success against Ceratitis capitata in Spain: a review

Background: The success of sterile insect technique (SIT) programs against many tephritid fruit flies, including Ceratitis capitata (Wiedemann), relies on the mating success of released sterile males in the field. Since its´ development in an area-wide concept, this control program is evaluated by the recapture ratio of sterile versus wild flies. This measure neither takes into account the real target of the SIT that is the wild female, nor does it give any clue about the success of released sterile males. Thus, the contribution of released sterile males to reduce the wild population still remains as a key issue. In this work we review recent findings on how sterile males contribute to reduce wild populations by means of analyzing the sperm content of wild females, as the real target of the SIT program. Methods: A mating competition test was initially performed in laboratory and then under semi-natural conditions, with different Ceratitis capitata Vienna-8 tsl release ratios. The efficacy of the SIT and its contribution to reduce wild population was assessed by determining the percentage of females mated with sterile male, with a sperm ID molecular test, and by linking to offspring production on sentinel hosts. Results: Statistical methods have been developed with the obtained data of sperm ID in the spermathecae of captured females and with data of viable offspring produced in sentinel fruits, revealing that both can be predicted using release ratio and mean temperature. Moreover, humidity arose also as a factor influencing the female capture in lured traps. A strong negative relationship was established between the proportion of Vienna-8 mated females and Ceratitis capitata offspring production, being a key point for a model to predict the SIT program success. Conclusions: The statistical models developed should contribute to enhance the efficacy of SIT programs against Ceratitis capitata by means of modulation of release ratios by season temperature and by checking wild female’s sterile sperm content.