A growing body of research has examined the effect of shared resource density on intraguild predation (IGP) over relatively short time frames. Most of this work has led to the conclusion that when the shared resource density is high, the strength of IGP should be lower, due to prey dilution. However, experiments addressing this topic have been done using micro- or mesocosms that excluded the possibility of intraguild predator aggregation. We examined the effect of shared resource density on IGP of an aphid parasitoid in an open field setting where the effects of prey dilution and predator aggregation could occur simultaneously. We brought potted soybean plants with 2, 20, or 200 soybean aphids (Aphis glycines) and 20 pupae ('mummies') of the soybean aphid parasitoid Binodoxys communis into soybean fields in Minnesota, USA. We monitored predator aggregation onto the potted plants, predation of parasitoid mummies, and successful adult emergence of B. communis. We found that predator aggregation was higher at the higher aphid densities on our experimental plants and that this coincided with lower adult emergence of B. communis, indicating that even if a prey dilution effect occurred in our study, it was overcome by short-term predator aggregation. Our results suggest that the effect of shared resource density on IGP may be more nuanced in a field setting than in microcosms due to predator aggregation.
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Acknowledgments We thank Jon Malespy, Simon Lueth, Sarah Gunderson, Sheena Ahrar, Mark Asplen, Zeynep Sezen, Christine Dieckhoff, Megan Slaughter, Ashley Chacón, Daniel Chacón, and John Chacón for field and laboratory help. David Andow, Elizabeth Borer, Christine Dieckhoff, and two anonymous reviewers provided helpful suggestions on a previous version of this manuscript. Funding for this work was provided by a United States Environmental Protection Agency (EPA) Science to Achieve Results fellowship to J. Chacón, and also by the University of Minnesota Agricultural Experiment Station. The EPA does not officially endorse this publication and the views expressed herein may not reflect those of the EPA.
- Apparent competition
- Binodoxys communis
- Biological control
- Soybean aphid