Context‐dependent effects of mycorrhizae on herbivore density and parasitism in a tritrophic coastal study system

Abstract

1. Stressful abiotic conditions and mycorrhizal fungi have both been shown to influence plant quality significantly, yet the interactive effects of these factors on relationships among plants, herbivores, and natural enemies remain unclear. 2. In this study, the results of a factorial field experiment are reported in which the effects of plant stress and mycorrhizae on density and parasitism of three herbivores of Baccharis halimifolia L. were examined. 3. Plant stress was increased by adding salt to the soil, and association with mycorrhizal fungi was increased by inoculating plant roots. 4. Inoculation with mycorrhizal fungi resulted in increased density of all three herbivore species, but the effects of mycorrhizae on parasitism varied by species and with soil salinity levels. For the gall maker Neolasioptera lathami Gagne, mycorrhizae decreased parasitism regardless of soil salinity levels. For the leaf miners Amauromyza maculosa Malloch and Liriomyza trifolii Burgess, mycorrhizae effectively negated the decrease in parasitism resulting from increased salinity. 5. The results of this study show that the effects of mycorrhizae on parasitism may be context dependent, and can be positive or negative depending upon species and environmental conditions.

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

“…However, addition of AMF to plants in the field had neutral (Gange et al, 2003(Gange et al, , 2005bColella et al, 2014) to positive effects on cell-content feeders, leaf miners and gall makers in several studies (Gange et al, 2003;Younginger et al, 2009;Moon et al, 2013;Ueda et al, 2013). Within the same study system, results may even vary between generations of insects.…”

“…In one study on Sea myrtle, Baccharis halimifolia, parasitism rates of two species of co-occurring leafminers (Amauromyza maculosa and Liriomyza trifolii, respectively) and a gall making fly (Neolasioptera lathami) by parasitoid wasps were all negatively affected by AMF application (Moon et al, 2013). AMF colonization resulted in more leaves per plant, which also had higher nitrogen levels, subsequently leading to healthier and potentially more strongly defended hosts, negatively affecting the respective parasitoids (Moon et al, 2013).…”

“…Several studies have incorporated higher trophic levels in the study of AMF-plant-insect interactions and in all of the studied interactions (n = 5) AMF presence had a negative effect on the performance or density of predatory insects (Ueda et al, 2013) or parasitoids (Gange et al, 2003;Moon et al, 2013). In one study on Sea myrtle, Baccharis halimifolia, parasitism rates of two species of co-occurring leafminers (Amauromyza maculosa and Liriomyza trifolii, respectively) and a gall making fly (Neolasioptera lathami) by parasitoid wasps were all negatively affected by AMF application (Moon et al, 2013).…”

“…Plant nutritional value (most importantly, nitrogen and sugar content) in the field can be positively affected by soil organisms (Gange and West, 1994;Gange et al, 2005a,b;Younginger et al, 2009;Moon et al, 2013;Brunner et al, 2015;Godschalx et al, 2015;Ryalls et al, 2016). Moreover, plant secondary defense metabolites, that play a role in the palatability of host plants, can be affected by soil organisms in the field (Wurst et al, 2008;Megías and Müller, 2010).…”

Microbial Root Mutualists Affect the Predators and Pathogens of Herbivores above Ground: Mechanisms, Magnitudes, and Missing Links

“…Root associates may also alter the quality of prey for natural enemies by their impacts on plant secondary chemicals, which occur both passively in the hemolymph and midgut of herbivores, or may be sequestered in herbivore tissues (Nishida, 2002;Lampert et al, 2011). For example, plant glucosinolates occurring within herbivore prey negatively affect a wide range of parasitoids (Gols and Harvey, 2009).…”