Well, Ted gets a point for the adult beetles – they are Mycetophagidae – and a species of Mycetophagus according to Arnett, although if the adult male beetle didn’t have a distinctive tarsal formula, I’m not sure I would have ever keyed it out. A coleopterist now has the specimens and a species identification may be forthcoming. The associated larva is not a Ciidae – I think these are restricted to polypore mushrooms and the habitat was a fleshy gilled mushroom, Pleurotus ostreatus. My inference that the larvae associated with these adult beetles is the same species is based on co-occurance, appropriate size, and lack of any alternative. I’ll see if I can get a specialist to agree, but larvae don’t seem to be especially well known.
I think I’ll have to give Kaitlin the win here, though, with three points: one for recognising the mite as a member of the Heterostigmatina (aka Heterostigmata), one for a creative (if wrong) story about the life history, and one for boldly guessing where no other acarologist dared.
The mite is, in fact, an undescribed species of Paracarophenax Cross, 1965 (Acariformes: Heterostigmatina: Acarophenacidae). Of the five described species in the genus (Magowski 1994), Paracarophenax dermestidarum (Rack, 1959) seems to be the only species that has been studied in any detail – it is a parasitoid of the eggs of a dermestid beetle. However members of other genera in the family are of considerable interest as biocontrol agents of stored product beetles.
For example, Acarophenax lacunatus (Cross & Krantz, 1964) is an egg parasitoid of a number or grain-infesting beetles (Oliveira et al. 2003a,b) including the Lesser Grain Borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). Adult female mites are phoretic on adult beetles. The mites detach from the beetle as eggs are laid. A mite attaches to the egg, swells up (physogastry), and as it kills the egg up to two dozen offspring develop inside the body of the mother mite (Faroni et al. 2000). One or two of these internal young are males and they mate their sisters before they pop open the mother and start looking for new eggs or new beetles to hitch rides on.
This seems to be the general life style of these mites, including those in the genus Adactylidium Cross, 1965 on thrips eggs and Aeithiophenax Mahunka, 1981 on the eggs of scolytine bark beetles. So, we may assume that our Paracarophenax does something similar. I’m not aware of reports of these mites attaching to larvae, but the three ‘Mycetophagus‘ larvae with mites were all large, plump, and probably prepupae (smaller larvae did not harbour mites). In the swampy morass of a decomposing oyster mushroom, I think it makes sense that the mites hang on (they were not feeding) to the late stage larva. One wonders where pupation takes place, but for the mites to have another generation, they need to hitch a ride on an appropriate insect.
Cross EA, Krantz, GW. (1964) Two new species of the genus Acarophenax Newstead and Duvall 1918
(Acarina:Pyemotidae). Acarologia, 6, 287-295.
Faroni LRD’A, Guedes RNC & Mathioli AL. (2000) Potential of Acarophenax lacunatus (Prostigmata:Acarophenacidae) as a biological control agent of Rhyzopertha dominica (Coleoptera: Bostrichidae). Journal of Stored Products Research, 36, 55-63.
Magowski WL. (1994) Discovery of the first representative of the mite subcohort Heterostigmata (Arachnidae:
Acari) in the Mesozoic Siberian amber. Acarologia, 35, 229±241.
Oliveira CRF, Faroni LRD’A, Guedes RNC. (2003a) Host egg preference by the parasitic mite Acarophenax lacunatus (Prostigmata: Acarophenacidae). Journal of Stored Products Research, 39, 571–575.
Oliveira CRF, Faroni LRD’A, Guedes RNC, Pallini A. (2003b) Parasitism by the mite Acarophenax lacunatus on beetle pests of stored products. BioControl, 48, 503–513.
Rack G. (1959.) Acarophenax dermestidarum sp.n. (Acarina, Pyemotidae), ein eiparasitic yon Dermestes arten. Z. Parasitenkunde, 19, 411-431.