Sugar provisioning increases parasitoid numbers in agroecosystems but may not reduce pest densities: A meta‐analysis

Abstract Parasitoids are pivotal to biological pest control in agroecosystems. Agricultural intensification has greatly reduced access to natural sugar‐rich food sources (mainly nectar and honeydew) sustaining parasitoid survival, fecundity and activity. In order to compensate for this shortcoming, sugar provisioning—through artificial sugar sprays or companion plants producing nectar or harbouring honeydew‐producing insects—has long been advocated as a way to strengthen biological control. However, empirical evidence remains fragmented if supplementing sugar resources overall enhances parasitoid activity and, ultimately, pest regulation across diverse crops and environments. We conducted a systematic review and a meta‐analysis of 80 publications assessing the field‐scale effects of sugar provisioning, from which 783 effect sizes related to parasitoid performance, pest densities and crop yield have been extracted. Across studies, we showed that sugar provisioning significantly increased the mean of parasitoid abundance (+28%) and parasitism rate (+26%) while reducing their variability, providing support that sugar resources benefit parasitoids. Despite enhanced parasitoid activity, pest density was not significantly reduced through studies and therefore not surprisingly either crop yield, revealing a likely dilution of the effects across trophic webs or compensation effects in the host population. Sugar source type (nectar vs. artificial sugars) and location (within or around crops) did not significantly alter the magnitude of effects. However, high heterogeneity in responses highlights their strong context dependence. Different types of publication bias (effect sizes shrinking over time, large effects from small studies being over‐represented) were also detected. Synthesis and application . Our findings demonstrate that providing sugar sources reliably supports parasitoid populations and parasitism rate but does not systematically translate into improved pest suppression or yield gains. These results suggest that, for economic and practical reasons, sugar inputs at the edge of cultivated fields should be favoured. However, because most available studies rely on indirect sugar provisioning via nectar‐producing plants, the specific contribution of sugar per se remains difficult to isolate and may be overestimated. More explicit tests of sugar provisioning are needed to better disentangle underlying mechanisms, identify limiting resources for parasitoids and better guide actions for conservation biological control.