Valorization of hop leaves for development of eco-friendly bee pesticides

AZUCENA IGLESIAS; GIMÉNEZ-MARTÍNEZ PABLO; MITTON G.; MEROI ARCERITO F.R.; FANGIO M F; CHURIO M S; SANDRA FUSELLI; FANOVICH A; EGUARAS M.; MAGGI M.

APIDOLOGIE

EDP SCIENCES S A

Lugar: Paris; Año: 2020

0044-8435

The bacterium Paenibacillus larvae and the mite Varroa destructor are two of the most severe biotic stressors affecting honeybees, and are responsible for American foulbrood and varroosis respectively. To control these pathogens, beekeepers regularly apply synthetic acaricides or antibiotics to parasitized hives. However, antibiotic and acaricide overuse over time leads to resistance in bacteria strains and mite populations respectively, not to mention the residual contamination of bee products with these chemicals. The development of alternative and effective control methods of bee diseases is therefore crucial. In recent years, natural substances from vegetable extracts have emerged as the basis of suitable control methods to treat bee colonies parasitized by both P. larvae and V. destructor. Our aim was to evaluate the bioactivity of ethanolic and methanolic hop leaf extract (Species: Humulus lupulus L, varieties: Victoria, Spalt and Cascade) against P. larvae, V. destructor and A. mellifera. the bactericide activity against P. larvae, the broth microdilution method was used. Topical administration protocols were used to determine the bioactivity of hop extracts on V. destructor and A. mellifera. Total polyphenols, flavonoids, saponines and antioxidant capacity were determined for each hop leaf extract tested. The Victoria extract had the highest concentration of phenolic compounds, whereas Cascade and Victoria extracts had higher concentrations of the glycoside saponine. All hop extracts presented low toxicity against A. mellifera bees after 48h of topical administration (except for Cascade ethanolic extract which reached a maximum of bee mortality). Minimum Inhibitory Concentration (MIC) and Minimum Bacteridicidal Concentrations (MBC) values ranged from 0.69 to 2.75 ppm for the Cascade variety; 1.38 to 5.5 ppm for the Spalt variety and 5.5 to 11 ppm for the Victoria variety. After 48h, the acaricidal activity for an ethanolic extract of the Victoria variety reached values close to 80%, while the methanolic extract of Cascade showed an acaricidal activity close to 70%. The results reported in this study support the potential use of methanolic and ethanolic extracts of hop leaves from Argentina as promising natural alternatives for varroosis and American foulbrood control.