Matthew Meisner with Dr. Anthony Ives

UW-Madison Department of Zoology

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 attack 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. Specifically, this research tests the hypothesis that, in the presence of spotted aphids, the foraging efficiency of A. ervi on pea aphids is diminished relative to that for P. pequodorum. Experiments were conducted in petri dishes, on single alfalfa plants, and in field cages to test this hypothesis. Petri dish experiments showed 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 suggested that neither parasitoid successfully parasitizes spotted aphids, even though both attack them. However, P. pequodorum accounted for a higher percent of overall pea aphid parasitism on plants with spotted aphid present during parasitoid foraging. Field experiments are ongoing. Results from petri dish and single plant experiments, however, suggest that spotted aphids distract A. ervi from pea aphids, so A. ervi expends time and eggs attacking spotted aphids when it cannot successfully parasitize them. This benefits P. pequodorum, which does not readily attack spotted aphids, by reducing competition for often limited pea aphid hosts.