Sinno, Martina (2017) Fitness reduction of Bactrocera oleae (Rossi) due to the alteration of the endosymbiotic bacteria titer. [Tesi di dottorato]

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Depending on the yearly fluctuations of the climate conditions, the olive fruit fly (Bactrocera oleae, Rossi) may cause severe damage and economic losses in the olive production due to yield reduction and degradation of products composition, quality, and properties (Pereira et al., 2004). The impact of this pest on the olive oil and olive table sector is frequently extremely detrimental and the average annual loss caused by olive fruit fly infestation is estimated to be 5% of the total world production with an estimated economic loss of 800 million US$ a year (Montiel Bueno & Jones, 2002). During the last 40 years, the control strategies of B. oleae have been based on the wide use of chemicals insecticides but since 1970, it is well known that B. oleae may potentially develop noteworthy levels of insecticides resistance (Tsakas & Krimbas, 1970; Stasinakis et al., 2001, Skouras et al., 2007) thus, traditional control strategies might lose their efficacy in the near future (Daane & Johnson 2010). Therefore, the development of noninsecticidal control strategies is essential to avoid the resistance occurrence reducing the selection pressure on the field populations (Daane & Johnson 2010). Furthermore, alternative control methods to chemical pesticides may significantly reduce the environmental impact of olive crop and guarantee a safer product for consumers (Saour & Makee, 2004). Recent studies demonstrated that the primary endosymbiotic bacterium of the olive fruit fly, “Candidatus Erwinia dacicola”, plays an essential role in the larval development in unripe olive fruits since B. oleae larvae that lack their specific endosymbiont cannot develop (Ben-Yosef et al., 2015). While some investigations on the olive fruit fly fitness advantages due to its endosymbiotic bacterium have been recently pinpointed(Estes et al., 2009; 2012; Ben-Yosef et al., 2010; 2014), little is known about the possibility of utilizing symbioticides compounds that may interfere with the “Ca. Erwinia dacicola" / Olive Fly interaction reducing the destructiveness of this widespread pest. Therefore, the identification of environmentally friendly compounds that could act as symbiosis inhibitors seems to be an interesting but poorly explored field of research that could lead to the development of new solutions/options to enhance the olive fruit fly integrated pest management. In the present study the efficacy of Copper Oxychloride and of some secondary microbial metabolites (Viridiol, Harzianic Acid, 6PP and Lipopepdides mixture)as symbioticides of B. oleae beneficial bacteria is verified. In vivo fitness tests were carried out to verify if the oral administration of these compounds lead to a fitness reduction in terms of adult mortality, females fecundity and capability of larvae to develop in unripe olive fruits. Furthermore, molecular analysis on the treated females were performed to achieve the quantification of the endosymbiotic bacterial titer in DNA samples of mid-gut and oesophageal bulb by qPCR.

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