Some plant essential oil constituents, such as monoterpenoids and phenylpropanoids, are promising insecticides in some situations and for certain insect pests. They vary in their toxicity, depending on the target insect. Moths (Lepidoptera) appear susceptible to these compounds, making them of promise for use against greater wax moths (Galleria mellonella Fabricius, (Lepidoptera: Pyrallidae), GWM), an important pest of western honey bee (Apis mellifera Linnaeus. (Hymenoptera: Apidae)) colonies. We determined the LC50 for GWM larvae or LD50 for GWM adults of select compounds (thymol, carvacrol, (S)-(+)-carvone, estragole, citral, linalool, (S)-(-)-limonene, and γ-terpinene). Concentrations between 8 and 2,266 µg/cm3 were mixed into the diets of GWM larvae and doses ranging between 0.08 and 70.3 mg per adult were applied topically to the abdomens of GWM adults. Lethal concentrations and doses were calculated after of 72 h of exposure. All eight compounds showed insecticidal activity against all tested stages of GWMs. Thymol (LC50 µg/cm3 (95% CI) = 21 [9-56], carvacrol = 46 [26-79], citral = 63 [30-134], and carvone = 76 [33-201]) had the highest toxicity toward GWM larvae. The hydrocarbons limonene (296 [231-377]), estragole (466 [354-611]), and γ-terpinene (729 [630-857]) had the lowest toxicity toward GWM larvae. Thymol had the highest toxicity towards GWM adults (LD50 (CI) = 0.5 [0.4-0.8] mg/adult). However, carvacrol (11.6 [10.1-13.6]), linalool (12.9 [9.3-17.8]), and limonene (15.8 [13.1-19.2]) were less toxic to GWM larvae. Our data show that select plant essential oil constituents are promising controls of GWM.
Keywords: Apis mellifera; Galleria mellonella; monoterpenoids; phenylpropanoids; toxicity.
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