I have spent the last two days reading everything I could find about Stratiolaelaps scimitus as a control for Varroa destructor. And my conclusion? It won’t work.
Some beekeepers report success, but the experiments—at least those I’ve been able to find—have been small and anecdotal with no statistical analyses. I understand that some larger and more rigorous tests are underway, but until results come in, I remain skeptical due to the life cycle and biological preferences of the Stratiolaelaps mite.
If you are unfamiliar with this creature, Stratiolaelaps scimitus (formerly known as Hypoaspis miles), is a predatory, soil-dwelling mite that has been used for the past fifteen years as a biological control agent against fungus gnats, spider mites, poultry mites, poultry lice, and similar agricultural pests. It lives, eats, and reproduces in the surface layers of the soil and is native to North America.
Since this mite has an appetite for other mites, beekeepers have been experimenting with introducing it into beehives in the hope it will eat Varroa destructor. A vermiculite medium containing the mites is usually sprinkled on a sheet of paper on the top bars. Apparently the mites, looking for breeding grounds, pass down through the hive, snacking on Varroa trail mix as they go in search of moist soil. Each Stratiolaelaps mite can eat up to five prey items per day.
Think of it this way: You and your friends live in New York City (the soil). One day you are scooped into a canister and dumped in Hartford, Connecticut (the hive) with no vehicle (wings). You decide the only way to get home is to walk (across the frames). So you head for home, stopping along the way to snack on hamburgers (Varroa). You and each of your friends eat five per day. Although this is a lot, there are an endless number stored in freezers (brood cells). Once you arrive in New York City (the soil) you have no incentive to go back to Hartford (the hive), you are tired of hamburgers (Varroa) and, in any case, the food is better at home (tender immature life forms).
Although Stratiolaelaps will eat Varroa destructor, they prefer eggs and immature arthropods rather than full-grown adult prey. And when they are “on the road,” traveling toward home, they can’t even get to the eggs or nymphs of the Varroa mite because those life stages are protected by sealed honey bee brood cells. Even when the home pantry is devoid of tender life stages, the Stratiolaelaps is perfectly happy with a diet of algae and plant debris, and will not go in search of Varroa burgers.
So, as a method of Varroa control, it lacks staying power. The Stratiolaelaps eat while they are passing through, but they don’t hang around, they don’t enter brood cells, and they can’t find patches of moist soil to breed in. All this means the Stratiolaelaps must be re-introduced multiple times per year just to lessen the number of phoretic Varroa mites.
Yes, I know there is a lot of excitement about them right now and they have a host of supporters, but when you look at the vital lifestyle issues, I don’t think the excitement is justified. It’s okay, you can call me Scrooge.