I was stymied by the "applicator license" requirement to purchase HopGuard in California.
I decided to investigate "homebrewing" of a analog. Has anyone else attempted this?
The patent describing HopGuard is available. COMPOSITIONS AND METHODS FOR CONTROLLING A HONEY BEE PARASITIC MITE
Gene Probasco http://www.google.com/patents?id=NV3OAAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false
The patent is worth reading, even if you have access to the commercial formulation. (Unfortunately, the patent was prepared by a clever lawyer who sought to broaden the claims, so the practical knowledge is buried under an expansion of duplicative but abandoned methods).
It is my understanding that HopGuard consists of 16% (by weight) beta-acid hop extract stabilized by converting to "soap" or Potassium salt and coating a cardboard strip. It appears the agent kills mites either by contact or by consumption into the bee's body fluid. I am not certain, but (from the patent) it appears the extract is made attractive to the bees by adding sugar.
Mr. Probasco tested a broad array of hop extract mixture against mites and honeybees (see Table 1). Three of his replicate tests had honeybee mortality: 5% Beta Acid on filter paper had 20% mortality after 22 hours, and 30% alpha-acid in water had 33% mortality. An isomorhized version of alpha-acid had 7% mortaility. Since higher and lower dosages of alpha and beta acid had no detectable mortality, the reason for the bee death is not clear, but Probasco did do replicate experiments. His method were to introduce bees to a filter paper lined petri dish, an easily replicated test for a home-brewed substitute.
Hops have three classes of active compounds: alpha-acids, beta-acids and hop oils. Alpha acids are used to provide "bitter" flavor and anti-microbial impact. Beta-acids are not bitter and have the same anti-microbial usage, but accompany the complex hop oils used to impart flavor. In modern industrial brewing, Alpha oil is extracted using liquid CO2, leaving behind the "base extract" (or the beta-acid and hop mixture). The base extract can be further refined to separate the hop oils from the beta-acid. Hop Oil can be injected into the finished beer at bottling to highten the flavor (called dry hopping in traditional brewing).
All three classes of compounds (and complex magnesium salt isomerizations) are available at the industrial scale. (footnote: beer is light sensitive, and the isomerizations were created to allow beer to be sold in clear rather than brown bottles without going "skunky" from sunlight exposure). Beta-acid is mostly a by-product. Beta acid is described as an addition to Sugar Beet processing to prevent Listeria micro-organism from growing. An interesting Japanese patent mixes Hops and Wasabi mustard extract to protect pickled vegetables from decay. Hops and Rosemary extract are sprayed on raw meat to prevent micro-organisims, oxidation and discoloring.
At the hobby level, online availabiltiy of unseparated extract of "Amarillo" hops is offered at 5ml (in syringes) for $1.99. Since dosage of HopGuard is 3.84 g per hive, the 5ml syringes would offer (very roughly) equivalent dosage but in an alpha-acid dominated combination. Hop extract are about 50% alpha, 30% beta, and 10% hop oil (depending on the cultivar). "Aroma oil" is also available (2 oz bottles) but this appears to be only the hop oil with the virtually all the active alpha and beta acids removed. Naturapathic herb outlets have water or alcohol extracts of "hops" in 1 to 4 oz bottles, but these have no accompanying analysis, so the concentration is guestimate. Raw or pelleted hops (in a dizzying variety of cultivars) are widely available. Pelleted hops are just cold ground and pressed hop cones. They could be extracted by boiling or placed in an expresso or french press coffeemaker. Pelleted hops are about 15% (by weight) active compounds, extraction values are low. Price is about $5/oz or $20/lb. Extraction of a pound of 15% product with a yield of 25% would generate 17 g of mixed acids, or about $1/gram. I suppose a NaOH solution might raise extractions, followed by a vinegar/ascorbic acid neutralization. This would allow a whole or pellet product to be roughly cost competitive.
The commercial product uses the beta-acid salt. At the hobbyist level, some cultivars of hops have higher "beta-acid" ratio than others, and some cultivars have a higher total compound. Modern selections are much higher in total compounds than historic varieties. Names showing high or relatively high beta level are: Mt Hood, Cascade, Crystal, Liberty. Names with exceptionally high total oil/acid are: Columbus, Galena, and a number of the new introductions.
The raw extract of hop acids and oils are unmixable in water or immiscable and are unstable. Industrially, a metal salt is added to produce a "soap" product that is dissolvable in solution and is stable on drying over the longterm. Patents describe the use of strong Potassium Hydroxide (KOH) or Lye (NaOH) to make the mixture alkaline (ph 9-11) followed by addition of acid (typically sulfuric) to neutralize and spray drying to create a powder.
Other patents (for use of hops in human foods) describe the addition of ascorbic acid or rosemary extract to provide anti-oxidant donors to protect the hop-oil from denaturing. Propolyene Glycol is often the base solution for hop oil mixtures.
Lecithin is mentioned only in passing in the patents. However, this is used frequently in "Bee" recipes to emulsify fats and oils with sugar solutions. For a home-brew approach using lecithin as an easily available emulsifying agent to make hop-extract mixable seems a good approach.
It is not clear to me from the patents whether the toxicity of hop oils during in ingestion by bees was addressed. The miticide property may come from both external grooming of the oil/acid/soap compound or ingestion. It may be a treatment that is more oriented to external spreading than ingestion will be safer.
One inexpensive approach may be to make a water/lectithin/sugar solution and boil pellets or whole cones in the solution and feed the mess of pellets/sugar to the bees in a feeding tray. I would want to perform the 100 bees in a petri dish toxicity assay on this.
Further information can be found in the patents.
COMPOSITIONS AND METHODS FOR CONTROLLING A HONEY BEE PARASITIC MITE
METHOD FOR PREPARING STABLE HOP POWDER
Naoto Yamaguchi et alhttp://www.google.com/patents?id=o0O_AAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false
Process for producing inorganic salts of hop acids
Kevin K. Madsen et alhttp://www.google.com/patents?id=8k-cAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false
Hop beta acid compositions for use in food products
Dennis L. Seman et alhttp://www.google.com/patents?id=GjKVAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false
Solid salts of hop acids
John P. Maye et alhttp://www.google.com/patents?id=PM4bAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false
Feeds containing hop acids and uses thereof as supplements in animal feeds
Francis L. Rigby et al http://www.google.com/patents?id=rkXtAQAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false
Antimicrobial compositions comprising hop acid alkali salts and uses thereof
Mitsunori Ono et al http://www.google.com/patents?id=VrilAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false