ANALYSIS OF FORAGING BEHAVIOR OF THE WHITEFLY PARASITOID ENCARSIA-FORMOSA (HYMENOPTERA, APHELINIDAE) IN AN EXPERIMENTAL ARENA - A SIMULATION STUDY

Foraging of Encarsia formosa was analyzed using a stochastic simulatio n model of the parasitoid's behavior. Parasitoids were allowed to sear ch during a fixed time in an experimental arena with immatures of the greenhouse whitefly, Trialeurodes vaporariorum. The model simulates ho st searching, selection, and handling behavior and the physiological s tate (egg load) of the parasitoid. The simulated number of hosts encou ntered, parasitized, or killed by host feeding agreed well with observ ations on leaf disks. The hypothesis of random host encounter seems to be correct. The number of ovipositions on the leaf at low host densit ies was strongly affected by the parasitoid's walking speed and walkin g activity, the probability of oviposition after encountering a host, and the initial egg load. At high densities, the initial and maximum e gg load were most important. A strong temperature effect was found at 18 degrees C or below. The number of encounters, ovipositions, and hos t feedings increased with host density to a maximum of 25, 6.5, and 1. 5, respectively, during 2 h at 25 degrees C. The shape of the curves r esembled a Holling Type II, which may be the result of the ''experimen tal'' procedure, where a parasitoid was confined to a patch during a f ixed time.