Hydrolats from Humulus lupulus and Their Potential Activity as an Organic Control for Varroa destructor

Area of Science:

• Agricultural Science
• Entomology
• Sustainable Chemistry

Background:

• Varroa destructor is a significant pest in apiculture, causing substantial economic losses.
• Residual hydrolats from hop essential oil extraction are often considered waste products.
• There is a need for effective and sustainable acaricides to manage Varroa destructor infestations.

Purpose of the Study:

• To evaluate the acaricidal potential of residual hydrolats from four hop varieties (Cascade, Spalt, Victoria, Mapuche) against Varroa destructor.
• To identify the active compounds responsible for the acaricidal activity.
• To assess the safety of hop hydrolats for adult honey bees.

Main Methods:

• Steam distillation was used for hop essential oil extraction.
• Residual hydrolats were collected and analyzed for chemical composition, including volatile oxidized terpenoids, polyphenols, flavonoids, and saponins.
• Acaricidal activity was determined by exposing Varroa destructor mites to varying concentrations of hydrolats, calculating LC50 values.
• Larval survival and adult bee mortality were assessed for each hop variety.

Main Results:

• Four hop varieties (Cascade, Spalt, Victoria, Mapuche) exhibited acaricidal properties against Varroa destructor.
• Victoria hydrolat showed the highest toxicity to mites (LC50: 16.1 µL/mL), followed by Mapuche, Spalt, and Cascade.
• Volatile oxidized terpenoids (e.g., β-caryophyllene oxide, β-linalool, isogeraniol), polyphenols, flavonoids, and saponins were identified as likely active compounds.
• None of the hydrolat extracts caused mortality higher than 20% in adult bees.
• Cascade hydrolat resulted in the highest larval mortality, while Spalt hydrolat showed the highest larval survival.

Conclusions:

• Residual hop hydrolats possess significant acaricidal potential against Varroa destructor.
• Victoria hop hydrolat is a promising candidate for developing sustainable acaricide treatments in beekeeping.
• The identified volatile compounds and phytochemicals contribute to the acaricidal efficacy.
• Hop hydrolats represent a viable valorization of a waste product for bee health management.