Insecticidal Activity of Some Major Essential Oil Components against Metopolophium dirhodum and Its Predators

Essential oils (EOs) are plant metabolites with important insecticidal effects. Nevertheless, information on the efficacy of the major substances on aphids and their natural enemies is still missing. The objective of this paper is, therefore, to identify the efficacy of selected EO majority substances-β-citronellol, carvacrol, isoeugenol, and linalool, including their binary mixtures-on the mortality and fertility of the aphid Metopolophium dirhodum, an important cereal pest. The best efficacy was proven for the binary mixture of β-citronellol and linalool (1:1 ratio), for which the estimated LC₅₀₍₉₀₎ is 0.56(1.58) mL L^-1. This binary mixture applied in sublethal concentrations significantly reduced aphid fertility. It was found that the phenomenon can be attributed to β-citronellol, as the females treated with LC₃₀ laid 45.9% fewer nymphs, on average, compared to the control. Although β-citronellol and linalool, including their 1:1 mixture, showed very good efficacy on aphid mortality, they were, on the other hand, very friendly to the larvae of Aphidoletes aphidimyza and Chrysoperla carnea, which are important aphid predators. Based on our results, the newly discovered synergically acting binary mixture β-citronellol/linalool can be recommended as an efficient substance suitable for the further development of botanical insecticides used against aphids.