214 Infestation of Fungus Cultures hy Mites 



mites make their way through cotton-wool plugs of culture tubes. Be- 

 sides destroying the culture they have entered, they may make accurate 

 subculturing a matter of difficulty by reason of the extraneous matter 

 — bacteria, fungus spores, etc. — they carry with them into the tube. 

 They wander rapidly from tube to tube and, unless discovered at an 

 early stage, the A^hole set of cultures in a laboratory may be either 

 destroyed or seriously contaminated. Even if the cultures be abandoned 

 and a completely fresh start made, another infestation may readily 

 take place from eggs laid in some unnoticed corner of the laboratory, 



2. Nature of the Infestation. 



Three species of mites were found contaminating cultures of which 

 Aleurobius farinae, De Geer, the Flour Mite, was the most abundant and 

 widespread. In many cases infection was slight; in others eggs, larvae 

 and adults were present but the mycelium was not noticeably destroyed 

 by this species. Tyroglyphus longior, Gervais, one of the cheese mites, 

 was observed in a few cultures. In most cases infection by this species 

 was very shght, but in three cultures of a species of the fungus Tricho- 

 derma the whole of the fungus was destroyed and the medium was 

 blackened with faecal pellets. Glyciphagus cadaverum, Schrank, was 

 found only in one set of cultures. The eggs of the two latter species were 

 not recorded. These three species are among those termed "Forage 

 Mites" as distinguished from " Mange Mites.'" They infect many kinds 

 of grain and flour and can frequently be found in the dust from crevices 

 in houses or stables. T. longior and A. farinae are also two of the species 

 that attack Stilton and Cheddar cheeses. The life histories of all three 

 species are very similar, consisting of four stages, egg, larva, nymph and 

 adult. That of T. longior has been described by Bales (i). The life cycle 

 is completed in four to five weeks, the eggs hatching about 10-12 days 

 after being laid. The larva is distinguished from the later stages by 

 having only three pairs of legs. It feeds actively for about a week, then 

 becomes quiescent and casts its skin, emerging as the first nymph. This 

 moults and becomes the second nymph which after a tliird moult emerges 

 as an adult male or female. There may, under favourable conditions, be 

 an additional hypopial stage, the hypopus being specially adapted for 

 distribution. It has a resistant skin and on the ventral surface there is a 

 sucker by which it can attach itself to flies, moths or human beings. The 

 fife cycle of A. farinae as described by Newstead and Duvall(2) is very 

 similar but usually shorter, varying from about 17 days in July to 28 

 days in the winter months. The eggs usually hatch in about 3-4 days. 

 There is only one nymphal stage and the hypopus is very rare. G. cada- 

 verum has a similar life history but the details are not well known. 



