Adding plant powders to supplemental bee feed
With continuing honey bee colony losses, practical and safe management options are essential. Nutrition is a key factor linked to A. mellifera colony failure (van Engelsdorp et al. 2010). Indeed, malnutrition is associated with greater susceptibility to pathogens (Alaux et al. 2010) and reduced pesticide tolerance (Wahl and Ulm 1983) and remains one of many reasons beekeepers supplement diets to improve colony performance (Retschnig et al. 2021). Accessible, low-risk fortified feeds during shortages may therefore help mitigate losses.
Agriculture has substantially reduced floral diversity available to A. mellifera (Naug 2009), increasing the risk of protein shortages. Decades of research have examined bee requirements, focusing on macronutrients (Pudasaini et al. 2020) and more recently micronutrients (Jovanovic et al. 2021; Brown et al. 2022a). Beyond macro- and micronutrients, researchers have examined supplements containing plant secondary metabolites (Hýbl et al. 2021). Phenolic compounds and flavonoids in honey and pollen (Cianciosi et al. 2018; Hýbl et al. 2021) can change detoxification gene expression, including cytochrome P450 enzymes (Mao et al. 2009), important in responses to pesticides and pathogens (Mao et al. 2013), and can increase worker longevity (Hýbl et al. 2021).
Studies have tested plant extracts against A. mellifera health parameters (Barker 1977; Pohorecka 2004; Roussel et al. 2015; Potrich et al. 2020), but the literature reviewed for this study appeared to contain no experiment simply adding whole-plant powders to bee food supplements. If effective, this would provide an accessible way to enrich diets and potentially improve health. Besides secondary metabolites, whole-plant powders may supply proteins, lipids, vitamins and minerals generally recognised as useful for bee health (Pudasaini et al. 2020), including the micronutrients examined by Jovanovic et al. (2021) and Brown et al. (2022a).
Beyond macro- and micronutrients, researchers have examined supplements containing plant secondary metabolites (Hýbl et al. 2021). Phenolic compounds and flavonoids in honey and pollen (Cianciosi et al. 2018; Hýbl et al. 2021) can change detoxification gene expression, including cytochrome P450 enzymes (Mao et al. 2009), important in responses to pesticides and pathogens (Mao et al. 2013), and can increase worker longevity (Hýbl et al. 2021). Studies have tested plant extracts against A. mellifera health parameters (Barker 1977; Pohorecka 2004; Roussel et al. 2015; Potrich et al. 2020), but the literature reviewed for this study appeared to contain no experiment simply adding whole-plant powders to bee food supplements. If effective, this would provide an accessible way to enrich diets and potentially improve health.
Whole-plant powders may also provide a combination of proteins, lipids, vitamins and minerals beneficial to A. mellifera (Pudasaini et al. 2020). Many studies use longevity (Amdam and Omholt 2002; Zhang et al. 2019; Hýbl et al. 2021) and body weight (Maurizio 1954; Oskay 2021; Brown et al. 2022a) as established health proxies. Published research continues to show that colony nutritional status is significantly correlated with changes in bee body mass across developmental stages, including larval size (Tasei and Aupinel 2008) and adult body fat (Alaux et al. 2010). Protein deficiencies in nurses reduce dry body weight and affect expected lifespan (Brodschneider et al. 2022).
Supplemental feeding is common, and nutrition directly affects A. mellifera mass and lifespan, making suitable feeding important in commercial beekeeping (Paray et al. 2021). This cage study tested whether workers would consume twelve plant powders and whether these affected weight and longevity. The results clearly show that plant powders can increase both body weight and lifespan in adult bees.
Body weight is commonly used as a health indicator because larger size is often associated with a greater foraging range and improved colony survival (Beukeboom 2018; Vanderplanck et al. 2021). Quercus spp., Melissa officinalis and Trigonella foenum-graecum significantly increased dry weight (Figure 2), along with mean or maximum longevity, or usually both (Table IV). Quercus is especially interesting. First, it is rich in phytochemicals such as antioxidants and has been systematically investigated in human disease research (Vinha et al. 2016). Second, Quercus bark, used here (Supplementary Table S.1), is naturally used by bees in propolis production (Cheng and Wong 1996).
Propolis has long been studied for antiviral, antimicrobial and other properties, including activity against pathogenic fungi, viruses and bacteria (Cheng and Wong 1996; Dolci and Ozino 2003; Muli and Maingi 2007). Plant leaves also contain variable carbohydrates, proteins and lipids (Reiss and Ruse 2023); M. officinalis and T. foenum-graecum contain these macronutrients (Srinivasan 2006; Jovanovic et al.). Further profiling would be useful because leaves probably added other beneficial nutrients to the sucrose solutions used here.
Unlike our findings, earlier research showed that Urtica dioica significantly increased adult worker weight (Pohorecka 2004). We did not detect this (Figure 2), but nettle leaf powder produced the longest predicted median lifespan among treatments: six days longer (Figure 3; Table IV).
Like Quercus, Urtica dioica contains polyphenols studied for human health benefits (Esposito et al. 2019; Dhouibi et al. 2020). It is also rich in vitamins such as C, B and K (Joshi et al. 2014; Bhusal et al. 2022), nutrients bees obtain from plant material or gut microbial symbionts (Brodschneider and Crailsheim 2010; Kwong and Moran 2016; Douglas 2017). In insects, biotin (B7) is needed for fatty-acid storage and metabolism, and folate (B9) for de novo nucleic-acid synthesis (Dadd 1973). In A. mellifera, pyridoxine (B6) is required for tasks including brood rearing (Haydak and Dietz 1972; Anderson and Dietz 1976). B vitamins contribute to colony performance (Jovanovic et al. 2021), but unsuitable doses may cause adverse effects, including elevated mortality (Brown et al. 2022a).
In conclusion, supplemental plant powders produced notably positive effects on worker weight and lifespan in this experiment, presumably through their nutrient content—vitamins, minerals and peptides—and phenolic compounds.
Adapted from Feeding with plant powders increases longevity and body weight of Western honeybee workers (Apis mellifera). Apidologie 55, 54 (2024). DOI: 10.1007/s13592-024-01094-4.
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