Study of the bio-ethology of Ceratitis capitata Wied. in Trentino and development of sustainable strategies for population control

The Mediterranean fruit fly (Medfly), Ceratitis capitata Wiedemann (Diptera Tephritidae), is a ubiquitous pest in subtropical and tropical regions worldwide. The gravid female deposits eggs inside the fruit and the newly emerged larvae feed on fruit pulp, causing fruit decay. The mature larvae leave the fruit and pupate in the soil, where new adults emerge. C. capitata is a highly polyphagous, multivoltine pest species and it is one of the world’s most economically important fruit pests. From its supposed origin in Africa, it has spread to a number of countries, including the Mediterranean, parts of South and Central America and Australia. It was first detected in southern Italy in 1863, from where it gradually spread northward and it now infests all major temperate fruit crops, including the apple, throughout the country. C. capitata is reported to complete up to seven generations per year in the most southerly regions and this number gradually decreases as the pest spreads northward. The northern limit of its distribution has been indicated to be around the 41st parallel north and its presence above this is considered to be occasional, mainly due to infested fruit trading, as this species is reported to be unable to overwinter above this latitude. The presence of C. capitata was first reported in a limited area of Trentino in 1990. After this initial report, it was not observed until 2010, when severe apple damage caused by C. capitata was reported in a much larger area. From this year on, Mediterranean fruit fly infestation regularly appeared in the warmest apple growing areas of Trentino, claiming the attention of local research institutes and demanding in-depth study of the bio-ethology of this Tephritid pest in relation to environmental conditions and the apple production system in this northern Italian region. The main objectives of this project were:  to select the most effective trap in order to implement an efficient monitoring plan;  to evaluate the susceptibility of apple varieties to oviposition and larval development in relation to physical-chemical parameter values at harvest time;  to monitor the flight activity of the fly at area-wide level;  to validate Tassan’s degree-day model (Tassan et al., 1982) for estimation of the length of life-cycles and number of potential Medfly generations in Trentino;  to assess the survival of overwintering populations;  to evaluate the efficacy of different insecticides in controlling Medfly fruit infestation. Four types of differently baited commercial traps (chromotropic, pheromone and food attractant) were compared in an apple orchard. A Decis® trap baited with a food attractant and catching both males and females was shown to be the most suitable for monitoring pests. In Trentino, adult Medfly flight starts during the first week of July, but the intensity (number of captures) remains at a very low level until August, when it begins to increase, peaking during September. After this, adult activity decreases in October and stops by the end of November. According to our observations, performed both in the open field and under controlled conditions, C. capitata overwinters at the larval stage in infested apples falling to the ground in orchards. The application of Tassan’s degree-day model based on temperature records provided a good estimate of first generation development (325.2 °DD from eggs to adult and 44 °DD for the adult preoviposition period) in the area where direct behavioural observations were carried out. To evaluate apple susceptibility, qualitative parameters (e.g. hardness, acidity, sugar and starch) of the main apple varieties cultivated in Trentino (Gala, Red Delicious, Golden Delicious, Granny Smith, Kanzi, Morgen and Fuji) were measured and correlated with the oviposition preference and larval survival of two Medfly strains in laboratory and field tests. The results showed that susceptibility to C. capitata oviposition increased when fruits had a high sugar content and a low penetrating resistance, as in the case of Golden Delicious, Kanzi and Fuji. In contrast, Granny Smith, Red Delicious and Morgen showed low susceptibility, due to their lower sugar content and higher peel and pulp hardness. As regards larval fitness, the results suggested that the tested varieties considerably affected various aspects of the biology of both immature and adult stages such as larval survival, duration of larval and adult developmental stage and size of the pupae. Golden Delicious, Gala, Kanzi and Fuji were the most favourable environments among the seven tested varieties. In contrast, Granny Smith, Red Delicious and Morgen were shown not to be favourable for larval and adult development. Two Medfly strains, one from Trentino and one from Spain, were used to assess the efficacy of five commercial insecticides containing the following active ingredients: Etofenprox, Cyazypir, Beta-Cyfluthrin, Spinosad and Thiacloprid. Sublethal doses of Spinosad and Beta-Cyfluthrin caused high mortality in Spanish strains. Moreover, Beta-Cyfluthrin, Etofenprox and Spinosad also reduced damage by females to apples at the recommended field rate. When used against the Trentino strain, Spinosad caused high adult mortality at the recommended field dose, while Cyazypyr and Etofenprox did not work sufficiently to prevent puncture, egg laying and larval development in fruit. Recommended field rates of all the selected insecticide formulations were repellent for egg-laying females of both strains, so both oviposition and fruit damage were significantly reduced on treated ripening fruits. The behavioural observations and experimental results obtained in this thesis allow a better understanding of the bio-ethology of C. capitata in a northern fruit growing region such as Trentino, providing fundamental information for advisors and growers to optimise the current pest management strategy. In the future, some of the results obtained in this study will be of great relevance for developing innovative and more sustainable control tactics.