Essential oil from Curcuma longa leaves: Can an overlooked by-product from turmeric industry be effective for myiasis control?

Curcuma longa L., popularly known as turmeric, is one of the most studied Curcuma species due to its rhizome, wide used as a dye, and its multipurpose uses in medicine, cosmetics, food flavoring and textile industries. However, the knowledge of essential oils (EO) from C. longa leaves is still limited. In turmeric production, the stems and leaves above the ground are considered waste products after harvesting. The present study was designed to assess the chemical composition of C. longa leaves EO (CLLEO) and investigate the bioactivities of its major constituent, α-phellandrene against third instar larvae (L3) of Cochliomyia macellaria (secondary screwworm). In addition, we intended to demonstrate through ultrastructural and histological assessment the morphological damages in L3. Groups of 20 L3 were placed on filter papers impregnated with increasing concentrations (0.31 to 2.86 μL/cm2) of CLLEO, determining mortality after 6, 24 and 48 h of contact. The compound α-phellandrene represented 41.99% of the EO. Other compounds were: α-pinene, β-pinene, myrcene, ρ-cymene, limonene and 1,8-cineole. The major compound of CLLEO, α-phellandrene was also tested (0.29 to 1.47 μL/cm2). C. macellaria mortality 48 h after contact with 1.27 μL/cm2 of CLLEO was 96.66 and 58.33% when using ethanol and acetone as solvents, respectively. The highest α-phellandrene dose assessed in this work (1.47 μL/cm2) presented a high mortality rate (96.66%). Structural analysis revealed marked lesions (cuticle surface dryness and severe degeneration on the spiracular plate) for both extracts. Histological sections of L3 showed necrosis of the intestinal tract and in the Malpighian tubules, and trophocytes with vacuolization. The brain had pyknotic profiles and vacuolar degeneration for both EO derivations. We suggest that CLLEO represents a sustainable bio-product for C. macellaria control that cause secondary myiasis to humans and animals.