Silicon accumulation in maize negatively impacts the feeding and life history traits of Spodoptera exigua Hübner

Silicon (Si) accumulation in plant tissues helps alleviate abiotic and biotic stresses, including infestation by insect pests. Here, we tested the hypothesis that Si concentration in maize leaves negatively impacts Spodoptera exigua Hübner (Lepidoptera: Noctuidae) with respect to: (i) feeding preferences; (ii) leaf digestion; and (iii) life history traits. We produced three groups of maize plants cultivated in a hydroponic system that had contrasting Si concentrations in their tissues (i.e., 0.21 ± 0.03, 4.45 ± 0.50 and 8.46 ± 0.61 g Si Kg-1 DW). In choice assays, fifth instars preferentially consumed leaves containing lower Si concentrations. In no choice-assays, we found that the approximate digestibility (AD) of larvae feeding on Si-enriched leaves was not affected. However, these larvae exhibited a 32% reduction in relative growth rates. Higher Si concentration in maize leaves extended larval development by three days; from 18.07 ± 0.29 when feeding on Si- diet to 21.39 ± 0.21 days on the Si++ enriched diet. Silicon also reduced larval survival by 18% and pupal weight by 20%. Our results confirm that Si supplementation in soil enhances the ability of plants to resist infestation with chewing insects, and should be considered as a viable option in the existing range of sustainable management practices.