Enhancement of Bioactivity of Common Ash and Manna Ash Leaf Extracts Against Spongy Moth Larvae Using a Chitosan–Gelatin Biopolymer Matrix

This study investigated the bioactivity of common ash (Fraxinus excelsior L.) and manna ash (Fraxinus ornus L.) leaf extracts, both in the crude form and incorporated into a biopolymer matrix, against spongy moth (Lymantria dispar L.) larvae. Chemical analysis revealed that both species were abundant in polyphenolic compounds, with common ash containing significant quantities of p-hydroxycinnamic acid derivatives and verbascoside, while manna ash was rich in coumarins, particularly aesculetin and aesculin. This study evaluated the feeding deterrent activity, contact and digestive toxicity, effects on larval nutritional indices, and larval development. Chitosan–gelatin-based biopolymer matrices containing the leaf extracts exhibited strong feeding deterrent activity at all tested concentrations, while crude leaf extracts showed moderate deterrence. The biopolymer matrices influenced spongy moth behavior only after digestion, resulting in reduced consumption and growth, as well as a prolonged duration of the third larval instar. No contact toxicity was observed for the biopolymer matrices. Incorporating leaf extracts into the chitosan–gelatin biopolymer matrix significantly enhanced their bioactivity against spongy moth larvae compared with crude leaf extracts. The results suggest that biopolymer matrices containing common ash and manna ash leaf extracts are promising environmentally friendly bioproducts for forest insect control, offering an innovative approach to managing spongy moth populations and protecting forest ecosystems.