Comparing olive fruit fly (Bactrocera oleae) density, fruit damage levels and parasitism rates in organic and conventional olive orchards in Crete, Greece

Abstract: The Olive Fruit Fly (OFF), Bactrocera oleae (Diptera: Tephritidae), is the main pest in olive agroecosystems causing quantitative and qualitative yield losses. Pest control is mainly done in conventional olive orchards by applying synthetic chemical pesticides. To reduce the use of pesticides and prevent pesticide resistance by the OFF, sustainable farming methods to control the OFF are needed. Here, we monitored OFF activity, fruit infestation levels, and parasitism rates by the larval parasitoid wasp Psyttalia concolor (Hymenoptera: Braconidae) for two consecutive years in twelve commercial olive orchards under two different farming systems, conventional vs. organic. The orchards were located in plain and hilly agroecological zones in the Messara valley, Crete. The aim of this study was to assess the effects of the pest management strategies of the two different farming systems. We found a higher OFF activity in organic orchards in both years. Fruit damage levels were higher in organic orchards only during the first year, while in the second year there were no differences, despite that conventional orchards were sprayed with pesticides to suppress the OFF. Interestingly, we found higher P. concolor parasitism rates in organic orchards which could explain reduced fruit damage as conditions in organic olive agroecosystem are favorable for maintaining beneficial insects. Findings show that even if higher OFF activity occurs in organic orchards, the more complex habitat may support the presence of the natural enemies of the OFF, leading to fruit infestation rates similar to conventional ones. The study may contribute to a holistic olive agroecosystem management and a more environmentally sound way to control the OFF.