Most terrestrial plants form associations with arbuscular mycorrhizal (AM) fungi, which are soil-dwelling microbial symbionts that provide plants with soil nutrients, while plants supply the fungi with carbon. The majority of these plants are also subject to herbivory from insects, thus tripartite interactions between insect herbivores, plants, and AM fungi are ubiquitous. This study assessed how aboveground herbivory from a generalist insect herbivore (Helicoverpa punctigera) affects the AM symbiosis in two C4 grass species (Bothriochloa macra and Dichanthium sericeum) and the consequences for host plant growth and nutrient uptake. Aboveground herbivory reduced root growth and carbon allocation belowground in both plant species, along with an associated reduction in arbuscular colonisation and phosphorus uptake. These findings suggest that, in accordance with the carbon-limitation hypothesis, herbivory can suppress the AM symbiosis by decreasing carbon belowground, potentially hindering AM fungal-enhanced nutrient acquisition from the soil.