Matthew Meisner with Dr. Anthony Ives

Department of Zoology, UW-Madison

This research explores a possible explanation for the persistence of a native North American parasitoid, Praon pequodorum, following the introduction of an exotic parasitoid with superior foraging efficiency, Aphidius ervi.  Both P. pequodorum and A. ervi successfully parasitize a common host, the pea aphid, which is abundant in alfalfa fields.  A second aphid species, the spotted aphid, is sometimes common in alfalfa.  Its presence may benefit P. pequodorum and allow it to persist with A. ervi. 

Experiments were conducted in petri dishes, on single alfalfa plants, and in field cages to test this hypothesis.  Petri dish experiments show that A. ervi is equally likely to attack pea and spotted aphids, while P. pequodorum is more likely to attack pea aphids.  Experiments on single plants in a greenhouse and in large field cages demonstrate that neither parasitoid successfully parasitizes spotted aphids, even though both attack them.  However, single plant and field experiments both suggest that P. pequodorum accounts for a higher percentage of overall pea aphid parasitism in the presence of spotted aphids.  Observations of parasitoid foraging behavior on single plants confirm that the foraging efficiency of A. ervi on pea aphids is drastically diminished in the presence of spotted aphids. Overall, results suggest that spotted aphids distract A. ervi from pea aphids, as A. ervi expends time and eggs attacking spotted aphids when it cannot successfully parasitize them.  This benefits P. pequodorum, which does not as readily attack spotted aphids,by reducing competition for often limited pea aphid hosts.