Diachasmimorpha longicaudata as Biological Control agent of the Mediterranean fruit fly, Ceratitis capitata: biotic and abiotic factors affecting its implementation in citrus crops of the Mediterranean basin

Abstract

Ceratitis capitata Wiedemann (Diptera: Tephritidae) is a cosmopolitan pest, originary from West-Africa, that has invaded almost all the temperate and tropical countries by the unwanted aid of the men. During its adaptation to these new environments, C. capitata has widened its host plant portfolio, being nowadays a key pest for more than 400 plant species of economic importance. Due to this importance, many importing countries had established quarantine measures and borders against fruit world-wide trade, which had directly impacted on the plant protection policies of producer countries. Spain and Tunisia are located in the Mediterranean basin; the first known world-wide dispersal point of C. capitata. In these two countries, C. capitata is considered a key pest mainly for citrus species and other soft-fruits. From a historical point of view, Plant Protection policies in Spain were switched from a nearly ecological management (with great losses) to mainly chemical-based treatments with the spread of organosphosphate compounds early on XX century. With the development of European Union, national Plant Protection plans were modified, introducing the Integrated Pest Management programs (IPM), on which environment and human-friendly methods should be selected instead of the most damaging chemical treatments. Following these steps, Tunisia is integrating the use of biorrational methods while keeping the use of chemicals as low as possible. To this end, in the present thesis dissertation, I would focus on the use of natural enemies as the best and sustainable control method, coming back to the Biological Control programs that were successful in the past against other pests in both countries. More precisely, this dissertation is presenting the results on the implementation of Classical Biological Control against C. capitata in citrus, by the importation, evaluation and release of the parasitoid species Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) in both countries. This parasitoid species, native from East Asia, is currently used against other tephritid pest species, key species for other countries and commodities. In the First Chapter I will present a literature review on the Plant protection policies against this key pest, and what is know about the performance and success of this parasitoid species. At the Second Chaper, I will present the results of the implementation of laboratory rearings of both insects to achieve all the remaining objectives, along with the determination of life parameters of the specie that will determine its success as natural enemy. In this second chapter I will also present the determination of biotic (host densities and availability) and abiotic (temperature, RH, rainfall) factors affecting the performance of D. longicaudata over C. capitata. During the Third Chapter, I will demonstrate that D. longicaudata is able to exhert control of C. capitata under natural Mediterranean climatic conditions when either challenging the parasitoid with hosts directly from the laboratory rearing or in a more natural condition, within the fruits, a forestep required to determine its inclusion in the national Plant Protection Policies. Results show that D. longicaudata exhert up to 30% of medfly population reduction by means of induced mortality along the provisioning of new parasitoid offspring that would propagate and establish in the country. Along these results I showed that D. longicaudata was able to control medfly infestation foci at a rate that depend on climatic conditions and on the number of released females. At the Fourth Chapter, I will reveal the results of D. longicaudata dispersion abilities along its capability to exhert control of C. capitata populations while applied joinly with SIT, by means of open-field test trials, with a new developed sentinel fruits methodology. In this chapter, I consider also the abiotic factors that could determine its naturalization in other Mediterranean countries with similar climatic conditions. The results of this chapter highlight the need of such dispersal studies at the corresponding local climatic conditions to establish the release procedures. At the Fifth Chapter, I will expose the results of importation and naturalization of D. longicaudata in Tunisia, with the required studies on the presence of native enemies and the identification of a new parasitoid Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae)., the establishment of laboratory rearings for the release trials, and the side-effects of the available control measures that will face D. longicaudata in Tunisian citrus orchards which will determine the procedure in tempo and form for the releases. At the end of this dissertation, I will present the main conclusions achieved that can be summarized in: (i) D. longicaudata is a viable natural enemy that can be successfully released in Mediterranean countries against C. capitata; (ii) Its biotic potential under the mild climatic conditions identified will help in the naturalization of this species, and in the establishment of release protocols, but also, (iii) its climatic requirements highlight the need of switching from Classical Biological Control to Inoculative Biological control, that means that both countries require mass-rearing facilities to provide these insects, along the involvement of growers in the application of IPM measures including the augmentoriums to facilitate the naturalization of the introduced species along the preservation of the native ones.