Biological Activity of Humulus lupulus (L.) Essential Oil and Its Main Components against Sitophilus granarius (L.)

Abstract

Besides its use in the brewing industry, hop cones appear as a powerful source of biologically active compounds, already checked for their putative anticancer, antimicrobial, and other bioactivities. Conversely, hop use in pest control remains to date under-investigated. Therefore, the biological activity of hop essential oil (EO) and its main constituents was investigated here against Sitophilus granarius. Adult contact toxicity was found 24 h after treatment with hop EO (LD50/LD90 13.30/40.23 µg/adult), and its three most abundant components, α-humulene, β-myrcene, and β-caryophyllene (LD50/LD90 41.87/73.51, 75.91/126.05, and 138.51/241.27 µg/adult, respectively); negligible variations at 48 h, except for α-humulene (LD50/LD90 26.83/49.49 µg/adult), were found. The fumigant toxicity of the EO and terpenes was also checked: in the absence of wheat grains, β-myrcene showed the highest inhalation toxicity (LC50/LC90 72.78/116.92 mg/L air), whereas α-humulene, β-caryophyllene, and the EO induced similar values (LC50/LC90 about 130/200 mg/L air); with the exception for EO, the wheat presence increased (30–50%) LC50/LC90 values. Moreover, EO and terpenes were perceived by insect antennae and elicited repellent activity. Only β-caryophyllene showed an anticholinesterase effect, this suggesting that different mechanisms of action should be responsible for hop EO toxicity. Therefore, hop EO appears suitable for developing control means against this pest.

Bioactivity of Wild Hop Extracts against the Granary Weevil, Sitophilus granarius (L.)

“…In this regard, the absence of major differences in both LD 50 and enzyme IC 50 among the several extracts strongly support the hypothesis of anti-AChE mediated toxic activity. Notice that anticholinesterase activity was already found in water and ethanolic extracts of several hop ecotypes [ 43 ], but not in the EO of the same ecotype used in this study [ 21 ].…”

“…In distinction with what reported for similar plant extracts [ 38 , 47 , 48 ], hop extracts did not show any inhalation toxicity. A moderate inhalation toxicity (LC 50 136.37 mg/L; LC 90 201.48 mg/L) was found for the EO obtained from the same hop ecotype [ 21 ]. These differences between solvent extracts and EO could be due to the occurrence of different bioactive compounds or to the loss of the volatile compounds exerting inhalation toxicity during crude extracts preparation.…”

“…Anticholinesterase activity of hop extracts was investigated [ 8 , 21 ] by detecting AChE activity photometrically (λ = 412 nm, 25 °C) by means of a Jasco V-570 spectrophotometer (Tokyo, Japan). Briefly, about 0.01 EU of enzyme (EC 3.1.1.7, from Electrophorus electricus , Sigma–Aldrich, Milan, Italy) were incubated in phosphate buffer (0.1 M, pH 8.00) plus 5,5′dithiobis(2-nitrobenzoic) acid (DTNB, 0.2 mM) either in the absence or in the presence of different aliquots of hop extracts.…”

“…Besides spent hop, wild hop also showed remarkable activity against pests, such as Colorado potato beetles ( Leptinotarsa decemlineata Say) (Coleoptera: Chrysomelidae) [ 17 , 18 , 19 ], as well as noxious insects and other invasive species [ 14 , 20 ]. Recently, wild hop essential oil (EO) and its main constituents (α-humulene, β-myrcene, and β-caryophyllene) proved to exert interesting properties against the granary weevil, Sitophilus granarius (L.) (Coleoptera, Curculionidae): A high contact and a lower inhalation toxicities, as well as a good repellent activity, were found against adult insects [ 21 ]. On the other hand, the limited yield of hop EO extraction may limit its use for pest control purposes.…”

Evaluation of biological activities of two essential oils as a safe environmental bioinsecticides: case of Eucalyptus globulus and Rosmarinus officinalis

“…Repetitions were carried out in triplicate for minimize errors with an oil-free control. The number of dead insects was recorded as a function of time after 24 h (Paventi et al, 2020).…”