Multi-target disruption of cuticular lipid homeostasis and cellular immunity by 2,6-dimethylphenol in the blowfly Lucilia sericata.

Abstract

The blow fly Lucilia sericata is a species of major medical and veterinary importance, functioning both as a causative agent of myiasis and as a beneficial organism in maggot debridement therapy. Increasing resistance to conventional insecticides highlights the need for alternative compounds targeting fundamental physiological processes. In this study, we investigated the insecticidal and physiological effects of 2,6-dimethylphenol (2,6-DMP), a lipophilic phenolic compound, with particular emphasis on its impact on cuticular lipid homeostasis and immune cell integrity. Topical application of 2,6-DMP significantly reduced larval survival and, more prominently, suppressed adult emergence to 5-20% of control levels, indicating disruption of metamorphosis beyond acute toxicity. Dose-response analysis revealed similar median lethal doses (LD50) for larvae and adults (∼1.85-1.95 μg/mg body mass), suggesting comparable susceptibility across developmental stages. Gas chromatography-mass spectrometry demonstrated pronounced, stage-specific remodeling of cuticular free fatty acids (FFAs). In larvae, exposure induced a strong, dose-dependent accumulation of long-chain FFAs, particularly C16:0 and C18:1. In contrast, adults exhibited a biphasic response: sublethal exposure resulted in a >3-fold increase in total FFAs, whereas lethal exposure caused near-complete lipid depletion. Cholesterol was consistently depleted in all treated groups. Principal component analysis confirmed that variation in lipid profiles was driven primarily by changes in total FFA abundance and sterol composition. In parallel, hemocyte analysis revealed clear immunotoxic effects, including reduced granulocyte abundance, impaired aggregation, and progressive morphological disruption in both in vivo and in vitro models. Collectively, these findings demonstrate that disruption of lipid homeostasis contributes to the physiological and immunotoxic effects of 2,6-DMP in L. sericata. Beyond revealing a potential mode of insecticidal action, our findings raise concerns about the potential ecotoxicological impact of 2,6-DMP as an environmental contaminant, particularly with respect to non-target insects, and identify lipid homeostasis as a sensitive mechanistic endpoint for environmental risk assessment.