Feeding preferences and functional responses of Calathus granatensis and Pterostichus globosus (Coleoptera: Carabidae) on pupae of Bactrocera oleae (Diptera: Tephritidae)
Carabid beetles are important predators in agricultural landscapes feeding on a range of prey items. However, their role as predators of the olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), one of the most serious pests of olives, is unknown. In this context, the feeding preferences and the functional responses of two carabid beetle species, Calathus granatensis (Vuillefroy) and Pterostichus globosus (Fabricius), were studied under laboratory conditions. Feeding preference assays involved exposing carabid beetles to different ratios of B. oleae pupae and an alternative prey, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Both species fed on B. oleae pupae however, C. granatensis always showed a significant preference for that prey whereas P. globosus switched to C. capitata pupae when the offered ratio was below 0.5. The total prey biomass consumed was significantly higher for P. globosus than for C. granatensis. Functional response curves were estimated based on different densities of B. oleae pupae and both carabid beetle species exhibited a type II functional response using Rogers' random-predator equation. P. globosus showed shorter handling time (1.223 ± 0.118 h) on B. oleae pupae than C. granatensis (3.230 ± 0.627 h). Our results suggest that both species can be important in reducing the densities of B. oleae in olive groves, although P. globosus was more efficient than C. granatensis.
