Effects of mycorrhizal fungi on insect herbivores: a meta‐analysis

Abstract

Mycorrhizal status of the host plant is often ignored in studies on plant-herbivore interactions, but mycorrhizal colonization is known to induce many morphological, physiological, and biochemical changes in host plants, which in turn may alter plant quality as a host for insect herbivores. Both positive and negative effects of mycorrhizal colonization of the host plant on performance and density of insect herbivores have been reported in previous studies. We have conducted a meta-analysis of 34 published and unpublished studies on this topic in order to find out the sources of variation in mycorrhizae effects on insect herbivores. Effects of mycorrhizae on chewing insects depended upon the parameter measured and the degree of herbivore feeding specialization. Density and consumption of chewing insects were higher on mycorrhizal plants, but this did not lead to greater plant damage, presumably because herbivore survival tended to be lower on mycorrhizal plants. Mono- and oligophagous chewers benefited from mycorrhizal colonization of their host plants, whereas performance of polyphagous chewers was reduced on mycorrhizal plants. Among sucking insects, phloem feeders benefited from mycorrhizal infection, but performance of mesophyll feeders was lower on mycorrhizal plants. The type of mycorrhiza was not important for chewing insects, but performance of sucking insects was increased more by arbuscular mycorrhizal fungi (AM) than by ectomycorrhizae (ECM). Among AM inoculation studies, the most commonly used fungal species, Glomus intraradices, tended to have a negative effect on chewer performance, whereas all other fungal species tended to have a positive effect. There was no significant difference in results between studies using inoculation and fungicides, field and laboratory studies, and published and unpublished studies. Mycorrhizal status of the host plant thus influences insect herbivore performance, but the magnitude and direction of the effect depend upon the feeding mode and diet breadth of the insect and the identity of fungi.

Effects of Soil Organisms on Aboveground Plant-Insect Interactions in the Field: Patterns, Mechanisms and the Role of Methodology

“…Suitable studies were selected first based on title and subsequently on abstract or full manuscript. Additionally, reference lists from suitable papers, as well as from recent reviews (Gehring and Bennett, 2009;Hartley and Gange, 2009;Koricheva et al, 2009;Pineda et al, 2010;Johnson et al, 2012;Soler et al, 2012;Wondafrash et al, 2013) on soil biotaplant-insect interactions were examined to detect additional publications. Lastly, for all suitable publications, the studies that cited these publications were scanned to detect additional studies that were published later.…”

“…EMF have been poorly studied within the soil biota-plantinsect framework and hence they are only briefly discussed. Relationships between AMF and aboveground insects, mediated by plants, are commonly reported in literature, and these effects have already been summarized in various other reviews (e.g., Pozo and Azcón-Aguilar, 2007;Gehring and Bennett, 2009;Hartley and Gange, 2009;Jung et al, 2012) and a meta-analysis (Koricheva et al, 2009). …”

Plant-mediated links between detritivores and aboveground herbivores

“…The impact on shoot herbivores by soil biota with a direct trophic link to the plant can be mediated by changes in water and nutrient uptake and/or an induction of plant defense that affects the whole plant systemically (reviewed by van Dam et al, 2003; Bezemer and van Dam, 2005; Koricheva et al, 2009; van Dam and Heil, 2011; Johnson et al, 2012). The same seems to be true for soil biota in indirect interaction to plants as summarized above for detritivores such as earthworms and Collembola.…”

“…In the first review articles on plant-mediated effects of soil biota on aboveground herbivores (Scheu and Setälä, 2001; Scheu and Setälä, 2001; Wardle et al, 2004) soil organisms were divided in two groups, either with or without direct trophic links to the plant. The majority of studies and reviews that have followed focused on soil biota with direct trophic interaction to plant roots such as root herbivores, pathogens, and arbuscular mycorrhizal fungi (reviewed by, e.g., Bezemer and van Dam, 2005; Koricheva et al, 2009; van Dam and Heil, 2011; Johnson et al, 2012). Soil organisms in indirect interaction with roots, such as members of the decomposer subsystem, have received far less attention (but see Wurst, 2010).…”

Unpredicted impacts of insect endosymbionts on interactions between soil organisms, plants and aphids

“…In addition, many plant sap-feeding insects host several types of microbial endosymbionts that supplement their nutritionally poor diet, modulate insect fitness and influence the outcome of trophic interactions (reviewed in [4,5]). For well-studied microbial symbionts of plants and insect herbivores, we can anticipate the influence of each individual host -symbiont pairing on plant -insect herbivore interactions [4,6]. However, such studies of two-way interactions (e.g.…”