Agathidium

WHEELER, QUENTIN D. & MILLER, KELLY B., 2005, Slime-Mold Beetles Of The Genus Agathidium Panzer In North And Central America, Part I. Coleoptera: Leiodidae, Bulletin of the American Museum of Natural History 2005 (290), pp. 1-95 : 16-17

COLLECTING AGATHIDIUM

Specimens of Agathidium species may be collected either by hand directly from host slime­molds or indirectly by means of certain mechanical contrivances or traps. The most difficult part about searching for Agathidium on Myxomycetes is developing an eye (i.e., search image) for the hosts. Sporocarps of Myxomycetes are so diverse in size, shape, and color that learning to recognize all or most of them as slime­molds is in itself an accomplishment (figs. 1, 2). Fruiting bodies vary from minute, stalked forms less than 1 mm in height to enormous cushionlike fruitions of Fuligo or dense patches of hairlike Stemonitis that may be more than a foot in diameter. Similarly, plasmodia vary from microscopic, transparent, amoeboid forms to the world’s largest polynucleated cells. Agathidium aristerium , for example, was first discovered breeding on a plasmodium of Physarum that was estimated to be larger than 4 feet in diameter! Some slime­molds are easily recognized, even in the plasmodial stage. Most are positively identified only with more careful, microscopic study ( Martin and Alexopoulos, 1969).

Once located, slime­molds may be removed with a piece of their substrate for closer examination. It is useful to hold a white sheet or a white box under the fruiting body while it is cut away from its substrate with a sharp knife blade. Sporocarps may be returned to the laboratory, where they can be spread upon a light­colored background un­ der the heat of a desk lamp for sorting. Beetles covered by host spores are amazingly difficult to see. However, once heated, beetles will become active and easily spotted and sorted from the mass of host spores. Vouchers of sporocarps may be kept by gluing them to the inner surface of the lid of a fungus specimen box and drying them completely.

Because plasmodia are easily damaged or desiccated, it is sometimes easier to simply examine them closely in the field. Both adult and larval beetles may be seen upon plasmodia since they lack the cover of spores afforded by mature hosts. Some plasmodia, particularly certain pigmented ones (such as the common yellow Physarum and Fuligo species ), can be induced to mature by exposing them to intense light as, for example, setting them in a Petri dish in direct sunlight on a window sill. They can be collected and kept in the laboratory on either agar plates or damp filter paper onto which are placed one or two flakes of old­fashioned oatmeal. Upon fruition, such forms may be positively identified. Mycologists sometimes have clues to plasmodial identification that can be very helpful to the entomologist. Mustard yellow plasmodia that stain brick red upon ‘‘bruising’’ (that is, touching them with one’s finger) are usually members of the genus Fuligo , though we do not know that similar bruising does not exist in other genera. Some plasmodia, including Fuligo , have a characteristic odor that can be quite strong when the plasmodium is expansive. Occasionally a plasmodium can be smelled before locating it visually. It has a sweet, earthy smell. Nonpigmented plasmodia are more difficult to see, such as the gray, jellylike Stemonitis plasmodium that can be quite substantial in size.

Flighted species may be collected using large­area flight­intercept traps of the kind described by Peck and Davies (1980). Both flighted and flightless species may be collected by sifting leaf litter, decaying wood, and similar substrates likely to include slimemolds and placing the siftate in a tullgren or Berlese funnel. This is particularly effective for collecting flightless species that are common in the Appalachians and Ozarks. In fact, during wet times of the spring and fall months in the Appalachians, sifting samples of mixed rhododendron­hardwood litter along mountain streams predictably yields one or more such species. In such circumstances leiodids often are exceeded in number of individuals only by carabids.