PREDATION ON ADULT APHYTIS PARASITOIDS IN THE FIELD

We report on predation on adult females of the parasitoids Aphytis aon idiae and A. vandenboschi (Hymenoptera: Aphelinidae) foraging in the f ield. During 89.6 h of observation, we witnessed 18 encounters with pr edators, 6 of which resulted in parasitoid capture. Three classes of g eneralist predators attacked Aphytis: spiders (unidentified Salticidae and Thomisidae), workers of the Argentine ant, Linepithema humile, an d nymphs of the assassin bug Zelus rendarii (Hemiptera: Reduviidae). A lthough observations were conducted during most months of the year, en counters with predators occurred only during September, October and No vember. During these months, encounters with predators occurred on ave rage every 3.2 h of observation, with one in three encounters resultin g in parasitoid capture. Peaks in predation coincided with population peaks of A. aonidiae, but were unrelated to population dynamics of any of the predators. We compare these results with previously published laboratory studies on longevity of Aphytis parasitoids, and conclude t hat predation pressure has the potential to severely limit parasitoid fitness in the field.