<p>Aphid–microbe–plant interactions are fundamental to understanding plant responses to combined biotic and abiotic stress. The grain aphid <i>Sitobion avenae</i> is a major pest of wheat, particularly under drought conditions. Although arbuscular mycorrhizal fungi (AMF) can enhance plant tolerance to water deficit, their effects on aphid performance across wheat cultivars differing in drought resistance remain unclear. We examined the influence of <i>Acaulospora delicata</i> on <i>S. avenae</i> performance on two wheat cultivars—Yunhan-618 (drought-resistant) and Xinong-1376 (drought-susceptible)—under well-watered and water-deficit stress conditions. Under water-deficit stress conditions, root colonization by <i>A. delicata</i> was higher in both Yunhan-618 and Xinong-1376 when compared to well-watered conditions. In the absence of mycorrhiza, nymphal developmental time was prolonged, especially on drought-stressed Xinong-1376 plants. AMF inoculation shortened developmental time, increased adult longevity, and enhanced fecundity of <i>S. avenae</i> under both water regimes. On Yunhan-618, AMF association increased intrinsic growth rate and reproductive output of this aphid. Honeydew excretion by <i>S. avenae</i> was greater on AMF-inoculated plants under well-watered conditions. Aphid body mass and water balance traits were generally higher on AMF-associated Yunhan-618 plants under adequate water supply. Aphids also preferentially settled on AMF-inoculated drought-susceptible wheat plants under both water regimes as compared to drought-resistant wheat plants. Overall, <i>A. delicata</i> enhanced plant drought resilience but simultaneously promoted aphid fitness. These findings underscore the complex and context-dependent role of AMF in shaping plant–aphid interactions, with important implications for pest dynamics under climate change.</p>