Biochar suppresses growth, pupation and eclosion success of Lepidopteran pests

Soil amendments such as fertilizers and other additives are widely employed to enhance soil fertility and crop productivity. However, the broader ecological impacts of these inputs are often under studied. Biochar, a carbon rich byproduct of pyrolysis of agricultural and forestry residues, has gained attention as a soil amendment for its soil-enhancing properties. While its benefits to soil health and plant growth are well-documented, its potential effects on herbivorous insect pests are less understood. Given that most lepidopteran pests pupate in soil, understanding how natural soil amendments like biochar affect these pests could lead to the development of innovative and sustainable pest control methods. To test this, we evaluated both direct and indirect effects of biochar through ingestion and alteration of pupation media on two lepidopteran pests, the generalist Spodoptera frugiperda and the specialist Manduca sexta. Our results show that biochar treatment significantly reduced the larval mass gain, pupal volume and adult traits of both pests. More interestingly, biochar exposure also delayed eclosion and reduced adult survival, with notable deformities observed in treated individuals. These effects were more pronounced at higher biochar concentration in both species. Collectively, we show that biochar can be further developed to complement current sustainable pest management strategies.