Insecticidal activity of essential oils from three Achillea species and associated gene expression responses in Rhyzopertha dominica

In this study, the insecticidal activity of essential oils (EOs) of three Achillea species of Türkiye [Achillea aleppica subsp. zederbaueri (AAZ), A. arabica (AA) and A. santolinoides subsp. wilhelmsii (ASW)] on the Rhyzopertha dominica were determined. GC-MS analysis identified camphor (41.0%) and eucalyptol (21.3%) in AA; camphor (41.6%) in AAZ; and borneol (21.1%) in ASW as major compounds. Insecticidal activity of EOs against R. dominica was found to be both dose and time-dependent, with higher concentrations and longer exposure leading to increased mortality. Notably, all EOs caused 99±1% mortality at 20% (v/v) within 24 hours (p < 0.05), while AAZ EOs exhibited the strongest effects even at 10% (v/v) concentration over extended exposure periods with 67.6±2.1% mortality. Although EOs are known to induce toxicity in insects, the molecular-level expression of key detoxification genes (GST, CYP450, and CarE) was analyzed for the first time in R. dominica exposed to EOs using qRT-PCR. qRT-PCR analyses revealed that the exposure to EOs significantly upregulated detoxification-related genes in R. dominica. Notably, 24 hours of exposure to AA EOs caused a 4.89±0.35-fold increase in the GST gene expression. Partial least squares (PLS) regression showed that the strong association between biological effects and chemical profile of EOs. The findings demonstrate that Achillea EOs act via direct toxicity and detoxification induction, highlighting their potential as eco-friendly biopesticides. However, high concentration requirements may restrict application; thus, future studies should develop synergistic formulations and nano-encapsulation to enhance efficacy and stability. © 2025 Har Krishan Bhalla & Sons.