Abstract
Captive invertebrates rarely display clinical signs or lesions prior to death. Their small size precludes most diagnostic procedures, and clinicians unfamiliar with invertebrate anatomy and physiology may not feel comfortable with examination, diagnosis, and treatment in these animals. Acariasis, however, is easily diagnosed as mites on giant species of millipedes, centipedes, roaches, beetles, spiders, scorpions, and snails, are usually conspicuous. Mites can easily be collected and examined using transparent tape, transferred to ethanol, and submitted to an acarologist for speciation. Treatment is often dismissed based on the empirical notion that mites on invertebrates are harmless to their host, yet a commensal relationship has only been reliably demonstrated for Androlaelaps (Gromphodorholaelaps) shaeferi, a mite found exclusively on Madagascar hissing roaches (Gromphadorhina portentosa).3-5 Any such assumption regarding mites on all other invertebrate hosts is unsubstantiated and should not impact our decision to treat or not to treat. Toxicity for invertebrate hosts of acaricidal drugs used on pet and domestic mammals is a much more valid treatment concern. Manual removal is labor-intensive and other methods such as alcohol swabbing or flour ‘shake-and-bake’ are stressful and potentially harmful to the host, but a novel option is being explored for the treatment of acariasis in large invertebrates.
For over a decade now, a variety of mites have been used to address pests in greenhouses.1 Hypoaspis miles is one such species of predatory mite that is commercially raised for the biocontrol of plant pests such as fungus gnats and thrips. These mites are sold under the scientific name H. miles but they may actually be Stratiolaelaps scimitus. They belong to a group of ubiquitous free-living predatory mites that are indiscriminate feeders, preying on other mites, small insects, springtails, mite and insect eggs and larvae, and even small nematodes. They are sold at a reasonable cost, admixed with chipped substrate by the liter, with each liter containing approximately 15,000 mites, in plastic jugs fitted with a dispensing lid. Upon release, predatory mites voraciously seek out prey, with each beige/whitish adult believed to consume 1 to 5 prey/eggs per day. When prey are exhausted, predatory mites will feed on each other, and eventually starve out. Years of use in commercial greenhouses attest to their efficacy, but actual scientific studies on these mites are scarce. Herpetoculturists first experimented with predatory mites to rid snakes of mite (Ophionyssus natricis) infestation in their collections. The general consensus, albeit anecdotal, is that treatment was successful. Similarly, anecdotal use of these mites to rid large arthropods and snails of Riccardoella spp. mite infestation met with success. Controlled trials have shown that Hypoaspis aculeifer, a close relative of H. miles, will actively feed on all stages of the red poultry mite (Dermanyssus gallinae) including eggs, and use of these and other predatory mites was investigated for poultry operations.2
Hypoaspis mites come with release instructions that should be followed closely. Invertebrates may be treated in their vivarium or moved to a simpler, sparingly furnished treatment tank for 3 to 6 weeks. Common sense is used to assist predatory mites in their quest for prey and optimize the chances of success. The vivarium is kept warm and humid as mites may otherwise dry out. The set up should ideally not allow for invertebrates to bury themselves, as mites will not live beneath soil surface. Invertebrates are examined weekly to determine if predatory mites are proliferating and parasitic mites dwindling. Preliminary trials at the Bronx Zoo with S. scimitus (H. miles) mites to rid giant Madagascar cockroaches, African giant millipedes (Archispirostreptus gigas), and Malayan giant stag beetles (Dorcus titanus) of mites has met with conflicting results, probably due to logistical issues rather than inefficacity of the predatory mites. Further investigations are ongoing.
Other applications have yet to be explored. For example, predatory mites are known to also feed on small nematodes, suggesting they could be used in established exhibits of reptiles and amphibians as an adjunct to anthelmintic treatment of rhabditid and strongyloid parasites. These worms are hard to eliminate, as vivaria typically offer ideal conditions for their motile larvae to develop. Zoo veterinarians need be aware of predatory mites and their potential use so that through trials we can fully explore their potential in a zoological setting.
Literature Cited
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2. Lesna I, Wolfs P, Faraji F, Roy L, Komdeur J, Sabelis MW. Candidate predators for biological control of the red poultry mite Dermanyssus gallinae. Exp Appl Acarol. 2009;48:63–80.
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