Soil‐Applied Silicon Does Not Affect the Performance of Aphis craccivora on Cowpea Genotypes

Cowpea ( Vigna unguiculata ) is an important crop in tropical regions, where infestations of the black aphid, Aphis craccivora Koch (Hemiptera: Aphididae), can significantly reduce productivity. Silicon (Si) fertilization has been proposed as a strategy to enhance plant resistance to herbivores, although its effectiveness varies among plant–insect systems, particularly those involving phloem‐feeding insects. This study evaluated whether soil‐applied silicon affects aphid performance and plant physiological responses in cowpea genotypes. Three greenhouse bioassays were conducted to assess genotype‐related variation in aphid preference and reproduction, the effects of two silicon sources, rice husk‐derived biochar and commercial silicon oxide, on aphid abundance and plant physiological traits, and temporal changes in plant susceptibility under aphid infestation. Genotype‐dependent differences were detected in nymph production, whereas adult colonization did not differ among genotypes, indicating that host suitability was primarily expressed at the reproductive level. Silicon supplementation increased leaf Si accumulation, with significant differences between genotypes; however, it did not affect aphid abundance, reproductive output, plant damage severity, chlorophyll‐related parameters, or temporal patterns of infestation. Notably, the Crioulo genotype accumulated significantly more silicon than BRS Novaera, yet this increase was not associated with reduced aphid performance. Overall, despite promoting silicon accumulation in plant tissues, soil‐applied silicon did not influence aphid performance or plant physiological responses under the tested conditions. These findings indicate that successful silicon uptake does not necessarily translate into enhanced resistance against aphids in cowpea.