Predation on adult Aphytis parasitoids in the field

We report on predation on adult females of the parasitoids Aphytis aonidiae and A. vandenboschi (Hymenoptera: Aphelinidae) foraging in the field. During 89.6 h of observation, we witnessed 18 encounters with predators, 6 of which resulted in parasitoid capture. Three classes of generalist predators attacked Aphytis: spiders (unidentified Salticidae and Thomisidae), workers of the Argentine ant, Linepithema humile, and nymphs of the assassin bug Zelus renardii (Hemiptera: Reduviidae). Although observations were conducted during most months of the year, encounters with predators occurred only during September, October and November. During these months, encounters with predators occurred on average every 3.2 h of observation, with one in three encounters resulting 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 that predation pressure has the potential to severely limit parasitoid fitness in the field.