The Mediterranean fruit fly Ceratitis capitata (Diptera; Tephrititade) is an important pest of citrus and other deciduous fruit trees. There is a need for sustainable pest management tools and the use of entomopathogenic nematodes have been explored for controlling the stages of medfly that occur in the soil. We have investigated further this approach by assessing the efficacy of commercially available entomopathogenic nematodes applied early on-season or off-season when the medfly populations are passing through their annual bottleneck period, aiming at reducing their population before the growing season. In laboratory experiments, the efficacy of commercial strains of Steinernema carpοcapsae, Steinernema feltiae and Heterοrhabditis bacteriοphοra and H. downesi at doses of (1.5 x 106 IJs/m2) and 2.5 x 106 IJs/m2, at 15C° and 25C° was assessed and Steinernema feltiae was found to result in up to 70% reduction of adult medfly emergence at a dose of 2.5 x 106 IJs/m2 and lower temperatures, confirming its superiority over other commercially available species. Further trials in citrus groves in Corinthos, Greece in Spring 2021 (early season) and Autumn 2021 (off-season) confirmed that a single application of S. feltiae at moderate dose regimes can provide about 62–65% suppression of adult medlfies. Therefore, a single, moderate dose application of entomopathogenic nematodes early or off-season, which is more economical feasible can provide significant suppression of overwintering medflies and can be safely integrated with other tools for medfly management.

BACKGROUND Entomopathogenic nematodes (EPN) show potential in controlling larvae of the Mediterranean fruit fly (medfly) Ceratitis capitate, but previous studies mainly concern species and strains that are not commercially available. The use of EPN for control of Mediterranean fruit fly is further hampered by the cost of using nematodes. In this study, the efficacy and residual activity of commercial strains of three EPN species, Steinernema carp omicron capsae, S. feltiae and Heter omicron rhabditis bacteri omicron ph omicron ra medfly) C. capitata, in the soil substrate and inside fruits were evaluated. RESULTS Suspensions of these species were applied at a dose of 1.5 mi m(-2) on a soil substrate wherein medfly larvae were added sequentially for a period of 4 weeks post application at 20 degrees C. S. feltiae provided the highest suppression up to 50% as assessed by adult medfly emergence because it had the highest immediate activity and long residual activity. Furthermore, S. feltiae, and to a lesser degree S. carpocapsae, were able to move and infect medfly larvae inside infested apples and oranges left in the surface of the substrate wherein EPN were applied, reducing significantly adult medfly emergence (60-78%). CONCLUSION These results support the efficacy and feasibility of applying a single, relatively low dose of S. feltiae in autumn, off-season, targeting overwintering medfly larvae with the scope of reducing the number of adult medflies emerging later in the new season.