COMPONENTS OF THE FUNCTIONAL-RESPONSE OF PERILLUS-BIOCULATUS (HEMIPTERA, PENTATOMIDAE)

Fifth instars of the hemipteran predator Perillus bioculatus (F.) were observed as they attacked neonate Leptinotarsa decemlineata (Say) lar vae on potato plants. Observations were conducted at prey densities ra nging from one to 100 prey per plant, and standard functional response models were fit to the predation rates obtained. Neither the type II nor the type III functional response curves provided a satisfactory fi t to the data. The observed attack rate was neither constant over all prey densities (as in the type II model), nor an increasing function o f prey density (as in the type III model). Instead, it declined over p rey densities from one to 25 and then increased substantially at the d ensity of 50. A possible explanation for the observed pattern is that area-restricted search following prey consumption led to additional su ccessful feeding events at high densities but not at low densities. Th e mean observed handling time was essentially equal to an estimate bas ed on the type III model and prey density did not have a significant i nfluence on per-prey handling times.