GREENHOUSE RED SPIDER. 



159 



Development of Female Mite from Egg to Adult. 



FEEDING HABITS AND DISPERSION. 



A mite which has become full-grown, on finding a suitable spot on the 

 under surface of the leaf, settles down to feed, and the results soon become 

 apparent on the upper surface. At first this injury shows as a few small 

 dead or corky specks, but as feeding continues these few are added to 

 until we find a small area literally made up of them. The mite also im- 

 mediately begins to lay eggs, which soon hatch into young mites. These, 

 however, usually remain feeding in the immediate vicinity of their birth, 

 thus causing more or less concentrated injury at different points on the 

 leaf where older mites have established themselves, forming what might 

 be termed different colonies. As these colonies increase in number the 

 feeding areas also increase, until finally they coalesce and cover prac- 

 tically the whole leaf. This is now absolutely useless to the plant and 

 worthless as a food supply for the large number of mites which inhabit it, 

 and they therefore migrate to other leaves. This migration may be up 

 the plant or may extend to the next plant, provided their leaves are in 

 contact. This new plant may have hitherto escaped injury so that the 

 basal leaves remain uninjured, while an infestation occurs part way up 

 the plant. In natural dispersion the migration is nearlj^ always by full- 

 grown females previous to the egg-laying period. In the majority of cases 

 dispersion within a greenhouse is accomplished wholly by natural agencies. 



In artificial dispersion the most important factors are the men engaged 

 in pruning, picking or "rolling up" cucumber plants. They pass from 

 an infested to a non-infested plant, but cari'y over infestation on their 

 clothing, hands or tools. This means of dispersion becomes exceedingly 



