Potential for entomopathogenic nematodes in biological control: a meta-analytical synthesis and insights from trophic cascade theory
Potential for entomopathogenic nematodes in biological control: a meta-analytical synthesis and insights from trophic cascade theory
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Date
2008
Authors
Denno, Robert
Gruner, Daniel
Kaplan, Ian
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Abstract
Entomopathogenic nematodes (EPN) are ubiquitous and generalized consumers of insects in soil food webs, occurring
widely in and agricultural ecosystems on all continents. Augmentative releases of EPN have been used to enhance biological
control of pests in agroecosystems. Pest managers strive to achieve a trophic cascade whereby natural-enemy effects permeate down
through the food web to suppress host herbivores and increase crop production. Although trophic cascades have been studied in
diverse aboveground arthropod-based systems, they are infrequently investigated in soil systems. Moreover, no overall quantitative
assessment of the effectiveness of EPN in suppressing hosts with cascading benefits to plants has been made. Toward synthesizing
the available but limited information on EPN and their ability to suppress prey and affect plant yield, we surveyed the literature and
performed a meta-analysis of 35 published studies. Our analysis found that effect sizes for arthropod hosts as a result of EPN addition
were consistently negative and indirect effects on plants were consistently positive. Results held across several different host metrics
(abundance, fecundity and survival) and across several measures of plant performance (biomass, growth, yield and survival).
Moreover, the relationship between plant and host effect size was strikingly and significantly negative. That is, the positive impact
on plant responses generally increased as the negative effect of EPN on hosts intensified, providing strong support for the
mechanism of trophic cascades. We also review the ways in which EPN might interact antagonistically with each other and other
predators and pathogens to adversely affect host suppression and dampen trophic cascades. We conclude that the food web
implications of multiple-enemy interactions involving EPN are poorly studied, but, as management techniques that promote the
long-term persistence of EPN are improved, antagonistic interactions are more likely to arise. We hope that the likely occurrence
of antagonistic interactions in soil food webs should stimulate researchers to conduct field experiments explicitly designed to
examine multiple-enemy interactions involving EPN and their cascading effects to hosts and plants.