Separating mites from their habitat by hand is time-consuming and inefficient. A much better representation of the fauna is obtained by using techniques that extract specimens en masse. Samples should be handled carefully to prevent the spaces within them collapsing and so blocking specimen escape routes.
This method is only suitable for mobile specimens because it depends on the tendency of Acari to move away from decreasing moisture. It was designed for extracting soil and leaf litter fauna, but vegetation, animal bedding, nests, dried foods, some faecal material and even small dead vertebrates can be processed this way. The basic apparatus comprises a mesh platform (with an aperture size of about 3 mm) resting on or just below the top of a supported funnel. A container of preservative, such as 70 per cent ethanol, is fixed onto or placed under the funnel’s spout.
Lay the sample onto the mesh. As it dries, specimens will move downwards until they eventually fall through the mesh, down the funnel and into the preservative. Soil blocks and cores, and vegetation such as moss mats, should first be inverted. Most Acari live in the upper layers and so the distance they have to travel out of the sample is minimized. Leaving samples to slowly dry at room temperature gives inhabitants plenty of time to escape. The time taken for complete drying depends on the sample size and composition. Small amounts of leaves dry out in two or three days, whereas soil blocks may take two weeks. Drying can be speeded up by shining an electric light bulb (40-75 watts) at the sample. However, if the rate is too rapid, delicate and slow-moving species may not be able to escape.
The contents of the collecting vessel can be emptied into a Petri dish or filtered prior to examination. Live specimens are obtained by putting damp paper towel in the collecting tube instead of preservative. For samples of loose fine material, put a layer of coarse-weave net curtain over the mesh. This reduces the amount of debris falling into the preservative, but still allows specimens to pass. There are many versions of this basic set-up (reviewed in Edwards & Fletcher 1971). The most well-known are the Berlese funnel (the sample-holding part of the funnel is contained in a hot water jacket) and the Tullgren funnel (an electric light bulb is hung over the sample). Barton (1995) devised a system for extracting ticks from soil and litter that lets them escape by both upward and downward movement.
Free specimens from plant material and dead animals by shaking the host in a bowl or plastic bag containing a weak detergent solution, e.g., of washing-up liquid. Remove the host and filter the solution. Acari have a water-repellent exoskeleton and the detergent (= wetting agent) helps to release them by reducing surface tension. The following method was devised for recovering ectoparasites from vertebrate hosts (Lipovsky 1951).
1) Put the body or pelt into a bag and refrigerate for at least a day to kill the ectoparasites.
2) Allow the sample to return to room temperature.
3) Shake the body for about 30 minutes in a jar containing detergent, e.g., washing¬-up liquid, as a wetting agent.
4) Remove the host, pour the solution into a tall jar and leave until the sediment containing the specimens settles (at least 15 minutes).
5) Carefully decant off as much fluid as possible without disturbing the sediment.
6) Pour the remaining liquid and sediment into a shallow dish and examine under a stereo microscope. Alternatively, separate out the specimens by passing the fluid through filter paper or a 100 µm aperture sieve.
Thind (2000) describes a flotation technique that has excellent recovery rates for mites infesting stored foods.
Shaking samples of loose dry material through a tier of sieves with increasingly fine mesh separates out mites and ticks. A top sieve with an aperture size of approximately 1 mm traps large pieces of debris, while a basal one of 80 micrometres (µm) catches specimens. A jet of water or alcohol directed onto the back of the basal sieve can be used to wash the specimens into a dish for examination.