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following plants : cucumber, melon, beans, roses, vine, peach, palm 

 and other plants in greenhouses and hotbeds, as well as on apple, plum, 

 pear, elm, lime, maple and aspen. The greater part of the records 

 refer to damage caused to cucumbers and melons. Spinning-mites 

 have been found in southern and central Sweden, but north of 

 Upsala (about 60° n. lat.) only three cases are known ; knowledge 

 of their distribution is, however, too incomplete to allow of any 

 conclusions. As regards enemies, only nymphs of a species of Coniopteryx 

 have been recorded, attacking Paraletranycfius ununguis, Jac. This 

 negative evidence is probably not wholly due to insufficient obser- 

 vations and it seems likely that the spinning-mites in Sweden have 

 very few natural enemies. The spinning habits of the mites are very 

 little known, which is very remarkable, as their biology in many 

 other respects has been very thoroughly investigated. It appears that 

 the different species vary much in this respect, some species, such as 

 T. telarius, spinning plentifully, while others, like Paratetmnychus 

 pilosus, hardly spin at all. It is important that these questions should 

 be investigated, as control must obviously vary in accordance with 

 differences in this respect, the spinning forms being better protected, 

 owing to their webs, than the other species. 



Based on a comparative morphological study of the species as yet 

 known, the author subdivides the genus into four genera. These are 

 Paratetranychiis; Zacher, of which the type is P. ununguis, Jac. ; to 

 this genus belong also P. pilosus, C. & F., P. simplex, Banks, P. 

 longipes, Banks, and P. pratensis. Banks. Schizotetranychus, gen. nov. 

 the type being S. schizopus, Zacher ; to this also belongs mylilnspidis, 

 Riley. Neotetranychus, gen. nov., the type being N. rubi, sp. n., 

 including also N. bicolor, Banks, and N. modestus. Banks. To 

 Tetranychus, Duf ., belong the greater part of the known species, viz : — 

 T. telarius, L., T. aUhaeae, von Hanstein, T. ludeni, Zacher, T. 

 tumidus, Banks, T. desertorum, Banks, T. weldoni, Ewing, T. borealis, 

 Ewing, and T.flavus, Ewing. 



In Sweden, the following species are known : The fruit-tree spinning- 

 mite, Paratetranychiis pilosus, C. & F. The spherical, red eggs of this 

 species are often found hibernating on apple and plum trees in 

 such quantities that these appear quite red. The eggs hatch at the 

 beginning of May, and during the summer at least four generations 

 develop. Warm weather favours propagation, and damage has 

 only been recorded when this is the case. The pine-tree spinning- 

 mite, Paratetranychiis ununguis, Jac, has been observed on Picea 

 excelsa, P. alba, P. sitchensis and P. engelmanni, as well as on larch and 

 pine ; it is undoubtedly indigenous to Sweden. The eggs hibernate 

 and there are at least four generations during a year. Severe damage 

 has as yet only been recorded from nurseries and on hedges. Neotetra- 

 nychus ruhi, sp. n., has only been recorded once, from wild raspberries 

 in the neighbourhood of Stockholm in the autumn. The greenhouse 

 spinning-mite, Tetranychus althaeae, von Hanstein, is the most injurious 

 species in the countrv, attacking especially cucumbers, melons and 

 beans. The attacks begin in May, continuing during June. July and 

 August unless combated. The number of generations is probably far 

 more than four. 



