> Is anyone aware of any research suggesting "probiotics" actually work?  

Medline lets me see some research. Found 2 that apply.

The first agrees with Cam's colleague on Nosema:

Ptaszyńska AA et al. Are commercial probiotics and prebiotics effective in the treatment and prevention of honeybee nosemosis C? Parasitol Res. 2016; 115:397-406.

The study was conducted to investigate the effect of Lactobacillus rhamnosus (a commercial probiotic) and inulin (a prebiotic) on the srvival rates of honeybees infected and uninfected with Nosema ceranae, the level of phenoloxidase (PO) activity, the course of nosemosis, and the effect on the prevention of nosemosis development  in bees...surprisingly, honeybees fed with sugar syrup supplemented with a commercial probiotic and a probiotic + prebiotic were more susceptible to N. ceranae infection, and their lifespan was much shorter [vs syrup alone]. The number of microsporidian spores in the honeybees fed for 9 days prior to N. ceranae infection with a sugar syrup supplemented with a commercial probiotic was 25 times higher (970 million spores per one honeybee) than in a control group fed with pure sucrose syrup (38 million spores per one honeybee)...In conclusion, the supplementation of honeybees' diet with improperly selected probiotics or both probiotics and prebiotics does not prevent nosemosis development, can de-regulate insect immune systems, and may significantly increase bee mortality.

The second suggests that a specific lactobacillus isolated from A. Cerana may have activity against EFB.

Wu M et al. Characterization of bifidobacteria in the digestive tract of the Japanese honeybee, Apis cerana japonica. J Invertebr Pathol. 2013; 112:88-93.

Bifidobacteria were isolated from the intestinal tract of the Japanese honeybee, Apis cerana japonica, and investigated for potential application as a probiotic agent against Melissococcus plutonius, the causal agent of European foulbrood (EFB), based on the findings of in vitro inhibition assays. A total of 11 bifidobacterial strains (designated as AcjBF1-AcjBF11) were isolated using a culture-dependent method and their 16S rRNA gene sequences were analyzed. The AcjBF isolates belonged to three distinct bifidobacterial phylotypes that were similar to those found in the European honeybee, Apis mellifera. Although the Japanese and European honeybees are distinct species with different traits and habits, the observation that they share highly similar bifidobacterial phylotypes suggests that bifidobacteria are conserved among honeybee species. Despite having extremely high 16S rRNA gene sequence similarities, the AcjBF isolates had markedly different carbohydrate fermentation profiles. In addition, in vitro growth inhibition assays revealed that the cell-free supernatants of all AcjBF isolates exhibited antagonistic effects on M. plutonius growth. These results indicate that the bifidobacteria isolated from the gut of Japanese honeybee could potentially be employed as a new biological agent to control EFB.

Close as I could get.

S

Skillman, NJ

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