High levels of arbuscular mycorrhizal fungus colonization on Medicago truncatula reduces plant suitability as a host for pea aphids (Acyrthosiphon pisum)

Abstract

This study sheds light on a poorly understood area in insect-plant-microbe interactions, focusing on aphid probing and feeding behavior on plants with varying levels of arbuscular mycorrhizal (AM) fungus root colonization. It investigates a commonly occurring interaction of three species: pea aphid Acyrthosiphon pisum, barrel medic Medicago truncatula, and the AM fungus Rhizophagus irregularis, examining whether aphid-feeding behavior changes when insects feed on plants at different levels of AM fungus colonization (42% and 84% root length colonized). Aphid probing and feeding behavior was monitored throughout 8 h of recording using the electrical penetration graph (EPG) technique, also, foliar nutrient content and plant growth were measured. Summarizing, aphids took longer to reach their 1st sustained phloem ingestion on the 84% AM plants than on the 42% AM plants or on controls. Less aphids showed phloem ingestion on the 84% AM plants relative to the 42% AM plants. Shoots of the 84% AM plants had higher percent carbon (43.7%) relative to controls (40.5%), and the 84% AM plants had reduced percent nitrogen (5.3%) relative to the 42% AM plants (6%). In conclusion, EPG and foliar nutrient data support the hypothesis that modifications in plant anatomy (e.g., thicker leaves), and poor food quality (reduced nitrogen) in the 84% AM plants contribute to reduced aphid success in locating phloem and ultimately to differences in phloem sap ingestion. This work suggests that M. truncatula plants benefit from AM symbiosis not only because of increased nutrient uptake but also because of reduced susceptibility to aphids.

Assessment of Local and Systemic Changes in Plant Gene Expression and Aphid Responses during Potato Interactions with Arbuscular Mycorrhizal Fungi and Potato Aphids

“…The response of aphids to AM fungal colonization of their host plants varies widely, from positive [24,[26][27][28][29][30][31] to neutral [13,14,[32][33][34][35] or negative [27,29,30,[36][37][38][39]. In general, specialist and generalist aphids benefit from feeding on mycorrhizal plants [16,24,[26][27][28][29][30]39], while specialist chewing herbivores, such as caterpillars, are negatively affected by AM fungal colonization of their host plants [13,16].…”

Variable effects of mycorrhizal fungi on predator–prey dynamics under field conditions

“…It is also possible that A. nerii abundances were not affected by AMF in this experiment. Whether aphids benefit, are unaffected, or are negatively affected by AMF colonization of their host plants depends on the plant and AMF species, plant age and developmental stage of the symbiosis (Garzo et al, 2020;Koricheva et al, 2009;Meier & Hunter, 2018b;Tomczak & Müller, 2017). Indeed, in this experiment, milkweed plants were older, and aphid populations developed over a much longer time, than in our previous greenhouse experiment (Meier & Hunter, 2018b).…”

Effect of Soy Leaf Flavonoids on Pea Aphid Probing Behavior

“…EPG variables describing aphid probing behavior were calculated using the Excel-VBA Macro [53], accessed from www.epgsystems.eu (accessed on 1 June 2021) and the means and standard deviations were subsequently calculated using the EPG analysis Excel worksheet created for this study [48,49]. In non-sequential variables (such as total durations of specific EPG waveforms and the number of EPG-recorded aphid activities), when a given waveform had not been recorded for an individual, the duration of that waveform was given the value of 0.…”

“…Aphid activities visualized as EPG waveforms were analyzed according to their frequency and duration and presented in a configuration related to activities in peripheral and vascular tissues. The interpretation of EPG variables in terms of plant suitability to the aphids follows the interpretation provided by detailed studies on aphid-plant interactions [27,28,30,31,40,41,45,46,48,49].…”