Insecticidal and immunotoxic actions of 2‐octenoic acid in the green bottle fly <i>Lucilia sericata</i> ( <scp>Diptera: Calliphoridae</scp> )

The blow fly Lucilia sericata is a medically and veterinary important species whose control increasingly requires environmentally safe alternatives to synthetic insecticides. This study evaluated the effects of 2-octenoic acid (C8:1), a medium-chain unsaturated fatty acid, on the survival, development and physiological integrity of L. sericata larvae and adults. Topical application of C8:1 caused significant mortality and developmental delays in a dose-dependent manner, with LD50 and LD100 values indicating greater susceptibility in larvae than in adults. Cuticular lipid profiling revealed profound alterations in free fatty acid (FFA) and sterol composition following treatment. Larvae exhibited progressive accumulation of medium- and long-chain FFAs (notably C16:0, C18:0 and C14:1) and depletion of cholesterol, suggesting weakened barrier integrity. In adults, sublethal exposure (LD50) resulted in marked lipid enrichment and incorporation of exogenous C8:1, followed by almost complete depletion of FFAs and cholesterol at lethal doses (LD100), reflecting metabolic collapse. Ethanol (solvent) treatment had minor effects compared with the strong lipid disruptions caused by C8:1. Haemocyte analyses demonstrated dose-dependent immunotoxicity, including granulocyte depletion, cytoplasmic shrinkage and increased proportions of plasmatocytes and oenocytoids, indicating impaired phagocytic and encapsulation responses. These combined effects-cuticular lipid disorganization, cholesterol depletion and haemocyte damage-suggest that 2-octenoic acid compromises both physical and immune defenses. The findings identify 2-octenoic acid as a promising bio-based insecticidal compound with multiple, non-neurotoxic modes of action, offering potential for integrated management of blow fly infestations while reducing risks associated with conventional insecticides.