We studied the interaction between the egg-pupal parasitoid Fopius (= Biosteres) arisanus (Sonan) (= Opius oophilus Fullaway) (Hymenoptera: Braconidae) and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) to assess the total impact of the parasitoid on the survival of this host. We tried to discover the factors determining host suitability, measure actual percent parasitism, and quantify host mortality by parasitization. Research was carried out applying dechorionation treatment, a non-destructive procedure that makes host eggshells transparent to microscopic observation, without interfering with development. We found that percent parasitism observed at the egg stage did not correspond to that detectable for emerging adults. In fact, parasitized host eggs were subject to a higher mortality than non-parasitized ones. Moreover, a certain percentage of the parasitoid eggs did not develop to the adult stage. Results from our study allowed us to measure the percent mortality by parasitization per parasitized egg. Furthermore, we analyzed the mortality factors due to parasitization acting during the host egg stage. Most of them had never been evidenced before and may help to explain this phenomenon. In particular, we found that the age of the host eggs exposed to parasitoids plays a fundamental role in the mortality by parasitization and that F. arisanus parasitizes C. capitata eggs more efficiently close to the time of eclosion.

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