92 



species is difi&cult to determine, the inert periods being passed within 

 the food substance. Approximately, the incubation period is 3 to 4 

 days, the larval period 4 to 5 days, of which the last two are spent in 

 inertia, and the nymphal period about 8 days, whether in one or two 

 stages is not known. The female deposits 8 or 10 eggs deep amont" 

 the foodstuff or in some convenient cranny. 



Cheyletus eruditus occurs in most grain infested with .Tyroglyphid 

 mites, upon which it is predatory, and is also highly cannibalistic. 

 It does not, however, occur in sufficient numbers to control the mites. 

 Parthenogenesis in this species has been proved in the breeding experi- 

 ments. Several successive generations have been bred in captivity 

 during the year without any male having been observed. It is possible, 

 however, that males may appear under certain conditions, or they 

 may be periodic, as in the Aphids. The eggs of C. eniditus are laid 

 in batches of from 20 to 30, often in the longitudinal groove of the 

 wheat grain, the female protecting the eggs until they begin to hatch. 

 Breeding goes on all the year round, but the life-cycle is much prolonged 

 in cold w^eather, or owing to shortage of food. The average period 

 from egg to adult is probably 36-40 days, the cycle during June being 

 approximately as follows : — Incubation period. 4 days ; larval period, 

 5 to 10 days ; 1st nymphal period, 5 to 17 days ; 2nd nymphal period, 

 7 to 20 days. There is generally a period of from 13 to 17 days between 

 the last ecdysis and the first oviposition. The external and internal 

 anatomy of this species is described. 



A new mite, a Tarsonemid, Acarophenax tribolii, gen. et sp. nov., 

 has been found during these investigations and is described. It is an 

 ectoparasite of the grain beetles, Triholium confusum, ¥., and 

 T. castaneuni, Hbst. ( ferrugineymn, Duv.), which do not attack sound 

 grain. The females of A. tribolii attach themselves to the eggs of 

 the beetles, from which they suck all the juices, becoming very 

 distended. A hole then appears in the Ventral surface, from which 

 as many as from 4 to 15 young mites emerge, males occasionally being 

 seen but never more than one from each parent. These young mites 

 attach themselves to the beetles, a preliminary period on the mature 

 host apparently being necessary for proper development, migration 

 to the egg then following. Many individuals die before migration 

 takes place. The morphology and systematic position of this mite 

 are discussed. 



It has become apparent during these investigations that, while 

 Acarids may be found in wheat at all seasons, it is during the warm 

 summer and autumn months tliat they are most plentiful and most 

 likely to occur in detrimental numbers. Not only is high temperature 

 the reason for this increase, but in the case of grain stored since the 

 previous autumn any process of deterioration due to bacterial activities 

 or to enzymes intrinsic to the wheat itself have had time to develoj) 

 and cause a large increase of moisture and a rise of temperature. It 

 is when such processes begin that mites generally occur in large 

 quantities. The connection between moisture content and the 

 presence of mites in grain is well known. Moisture determinations 

 of mite-infested stocks show that mites do not injure wheat and flour 

 in which the moisture is 11 per cent, and under, whatever the tempera- 

 ture may be. From 13 per cent, upwards the conditions are very 

 favourable for serious infestation. Under favourable moisture 



