Prickly Poppy and Castor Bean Extracts Show Promise Against Varroa Mites

For decades, beekeepers around the world have fought a relentless war against Varroa destructor, the ectoparasitic mite that ranks as the single greatest health threat to honey bee colonies globally. Now, a new field study from Mexico offers a promising glimpse of hope, demonstrating that simple hydroethanolic extracts from two common plants—Argemone mexicana, the Mexican prickly poppy, and Ricinus communis, the castor bean—can significantly reduce phoretic mite infestation in productive honey bee colonies under real-world conditions.

The research, conducted in Ciudad Victoria, Tamaulipas, Mexico, and published in Frontiers in Bee Science, evaluated the effects of these botanical extracts at three concentrations—10%, 15%, and 20%—across thirty-five Jumbo-type hives, each housing approximately 60,000 adult bees. The colonies were randomly assigned to seven experimental groups of five colonies each: six groups received botanical treatments while one served as a vehicle control, receiving only 70% ethanol without plant material. Treatments were applied by spraying directly onto bee-covered frames and internal hive surfaces on days 1, 7, 14, and 21 of the experimental period.

The results were striking. Colonies treated with the highest extract concentrations showed the lowest final phoretic infestation levels, dropping from a baseline of roughly 8% to just 3.61% for 20% Argemone mexicana and 3.44% for 20% Ricinus communis. In contrast, the vehicle control group saw its infestation rise to 9.08% by the end of the trial. The estimated effectiveness in reducing phoretic infestation, calculated using the Henderson and Tilton equation, reached 58.05% for R. communis at 20% and 55.65% for A. mexicana at 20%, with a clear concentration-dependent response across all treatments.

Mite fall—the number of mites dropping onto sticky monitoring boards placed beneath the colonies—told a complementary story. Colonies treated with 20% extracts consistently exhibited the highest mite fall values throughout the four applications, peaking at 10.1 ± 0.73 mites per application for R. communis and 9.7 ± 0.69 for A. mexicana during the third treatment. Vehicle-control colonies maintained minimal mite fall, never exceeding two mites per application. The mixed-effects model revealed significant effects of treatment (F = 47.35, p < 0.0001), application time (F = 14.87, p < 0.0001), and the treatment × time interaction (F = 1.91, p = 0.0313), confirming that repeated applications were associated with greater mite fall, particularly at higher concentrations.

Beyond the acaricidal results, the study provided a detailed phytochemical characterization of both extracts. Argemone mexicana consistently outperformed Ricinus communis in total phenolic compounds, flavonoid content, and condensed tannins. At the 20% concentration, A. mexicana extracts contained 182.5 ± 5.2 mg gallic acid equivalents per gram of dry matter in total phenolics, 74.4 ± 2.6 mg quercetin equivalents per gram in flavonoids, and 21.7 ± 1.0 mg catechin equivalents per gram in condensed tannins. Antioxidant activity, measured through ABTS, DPPH, and FRAP assays, followed the same pattern, with A. mexicana at 20% showing the strongest radical scavenging capacity and the highest ferric reducing power.

Correlation analysis revealed strong and significant associations between phytochemical composition and antioxidant activity. Flavonoid content showed the strongest correlations with antioxidant parameters, including a nearly perfect positive relationship with FRAP values (r = 0.9672, p < 0.0001) and strong negative correlations with ABTS and DPPH IC50 values (r = −0.9552 and r = −0.9543, respectively). These findings suggest that flavonoids may play a major role in the antioxidant capacity of the evaluated extracts, although the authors caution that antioxidant properties should be interpreted as complementary chemical characteristics rather than direct evidence of the mechanisms responsible for acaricidal activity.

Perhaps the most intriguing finding emerged from the relationship between mite reduction and honey production. While neither plant species, extract concentration, nor their interaction had a statistically significant effect on honey yield, Pearson’s correlation analysis identified a strong positive association between acaricidal effectiveness and honey production (r = 0.794, p < 0.0001). Colonies showing greater reductions in phoretic Varroa infestation also tended to produce more honey, with linear regression indicating that acaricidal effectiveness accounted for 63.1% of the variation in honey yield (R² = 0.631). Colonies treated with 20% A. mexicana showed a trend toward the highest honey production at 17.4 kg per colony, followed by 20% R. communis at 16.4 kg.

The authors are careful to note several important limitations. The alcohol-wash method quantified only phoretic mites on adult bees, not mites reproducing within capped brood cells, so the observed reduction cannot be interpreted as an equivalent reduction in the total colony mite population. Additionally, because the viability of fallen mites was not assessed, increased mite fall should not be interpreted as confirmed acaricidal mortality—it may have resulted from direct toxicity, repellency, disturbance caused by spraying, increased grooming by bees, or mite detachment from adult bees. The study also did not identify individual metabolites through chromatographic or mass spectrometric techniques, meaning the specific compounds responsible for the biological activity remain undetermined.

Safety considerations loom large as well. Both plant species contain biologically active and potentially toxic secondary metabolites, including alkaloids in A. mexicana and potentially toxic constituents associated with R. communis. The study did not perform residue analysis to determine the presence of plant-derived constituents in honey from treated colonies, and the authors explicitly state that the results cannot establish the chemical safety of these preparations or their suitability for human consumption. No synthetic acaricide reference treatment was included, and no completely untreated group was present, so the observed efficacy cannot be benchmarked against currently used acaricides.

Despite these caveats, the findings represent a meaningful step forward in the search for sustainable alternatives to synthetic acaricides such as amitraz, fluvalinate, and coumaphos, whose continuous use has led to resistant mite populations and raised concerns about chemical residues in hive products. The concentration-dependent biological activity demonstrated under field conditions, combined with the positive association between mite reduction and honey production, supports further investigation into these botanical preparations as potential components of integrated Varroa management strategies. Future studies incorporating LC-MS/MS, HPLC-DAD, or GC-MS analyses to identify and quantify major bioactive constituents, along with comprehensive residue, toxicity, and honey bee safety assessments, will be essential before these botanical extracts can move from the laboratory bench to the beekeeper’s toolkit.

Subject of Research: Botanical Acaricides for Varroa Mite Control

Article Title: Phytochemical composition and acaricidal potential of Argemone mexicana and Ricinus communis extracts against Varroa destructor in Apis mellifera colonies

Article References: Reyna-Fuentes, J. H., & Corona, M. (2026). Phytochemical composition and acaricidal potential of Argemone mexicana and Ricinus communis extracts against Varroa destructor in Apis mellifera colonies. Frontiers in Bee Science, 4, Article 1939011. https://doi.org/10.3389/frbee.2026.1939011

Image Credits: AI Generated

DOI: 10.3389/frbee.2026.1939011

Keywords: honey bees, Varroa destructor, botanical pesticides, Argemone mexicana, Ricinus communis, beekeeping, integrated pest management, Phytochemical, composition, acaricidal, potential, Argemone