200 MITES AND TICKS 



hypopus and differs completely from all the others. Instead of 

 having a flexible cuticle it is well chitinised and devoid of a mouth: 

 it does not appear to be formed as the result of adverse conditions 

 but acts as a means of dispersal. By means of a ventral sucker plate 

 through which project a series of finger-like suckers, the hypopus 

 attaches itself to a passing insect and is carried from one place to 

 another. At the same time it is able to survive drier conditions than 

 the adult. 



It has been found that a temperature of 23° to 25° C is the opti- 

 mum for rearing cultures of the furniture mite, Glycyphagus 

 domesticus and temperature and humidity have a marked effect on 

 the development of the tgg and hypopus stages. 



The life cycle of the feather mites, family Dermoglyphidae, is as 

 follows: there are two types of tgg, a hard shelled and a thin shelled 

 one. The latter contain larvae while still within the mother who 

 may be either viviparous or ovoviviparous. The six-legged larva 

 hatches from the egg to moult to the eight-legged protonymph 

 which in turn forms the deutonymph. When mating takes place the 

 male always copulates with the female deutonymph which later 

 moults to the adult stage. 



Detailed knowledge of the development of the larvae and nymph 

 of the Oribatid mites is virtually non-existent, but Sengbusch 

 (1954) has recently succeeded in timing the development of three 

 American species of Galumna from egg to adult. Oviposition may 

 occur in nature from spring to autumn and is probably correlated 

 with temperature which also affects the time of development. This 

 averages 63 days at 20° C in G. nervosus, but only 47 days at 25° C. 



Finally, we come to the sub-order Tetrapodili. Not until Keifer's 

 work (1946) on the alternation of generations of the buckeye rust 

 mite Oxypleurites aesculifoliae was the life cycle of any of the 

 Eriophyidae fully understood. The deutogynes become active in 

 late winter and leave their hibernating quarters on twigs. When the 

 buds swell in February they penetrate the outer scales and feed on 

 the green inner tissue beneath. With the development of leaves, 

 they lay eggs which hatch into nymphs producing primary mites 

 on the leaves. These soon produce additional primary mites. In 

 early May new deutogynes appear which when fully fed travel 

 down the stem for six inches or more and then crawl into crevices 



