As a result of climate change, temperate regions are facing the simultaneous increase in water and heat stress. These changes may affect the interactions between plants and pollinators, which will have an impact on entomophilous crop yields. Here, we investigated the consequences of high temperatures and water stress on plant growth, floral biology, flower-reward production, and insect visitation of five varieties of common buckwheat (Fagopyrum esculentum), an entomophilous crop of growing interest for sustainable agriculture. The plants were grown under two temperature regimes (21 °C/19 °C and 28 °C/26 °C, day/night) and two watering regimes (well-watered and water-stressed). Our results showed that the reproductive growth was more affected by drought and high temperatures than was the vegetative growth, and that combined stress had more detrimental effects. However, the impact of drought and high temperatures was variety-dependent. Drought and/or high temperatures reduced the number of open flowers per plant, as well as the floral resources (nectar and pollen), resulting in a decrease in pollinator visits, mainly under combined stress. Although the proportion of Hymenoptera visiting the flowers decreased with high temperatures, the proportion of Diptera remained stable. The insect visiting behavior was not strongly affected by drought and high temperatures. In conclusion, the modification of floral display and floral resources induced by abiotic stresses related to climate change alters plant–pollinator interactions in common buckwheat.