INSECTS 



175 



bark louse, as it is sometimes called, is much more prevalent, and 

 occasionally becomes so numerous as to destroy a tree. Generally, 

 however, this and the scurfy scale are kept in check by efficient 

 parasites. From a study of the history of these scales, we find 

 that the females lay eggs under the scale covering in the fall of 

 the year and subsequently 

 die. The eggs live over 

 winter and hatch the follow- 

 ing season, about the last 

 of May or the first of June. 

 At this time the unprotected 

 larvae crawl about over the 

 tree, looking for a place to 

 settle. This is the time 

 when they should be at- 

 tacked. The young larvae 

 may be readily destroyed by 

 almost any contact insecti- 

 cide, such as whale-oil soap 

 or kerosene emulsion, if it 

 is applied before they have 

 a chance to form their scale 

 covering. 



San Jose scale (Aspidiotus 

 perniciosus, Comstock). The 

 San Jose scale belongs to 

 the category of sucking in- 

 sects, and takes its food in 

 a liquid form by means of 

 a long, bristlelike proboscis 

 inserted into leaf or limb or 

 fruit, as the case may be. 

 Its habit of feeding renders it immune to treatment with arsenical 

 poisons, which must be taken internally to be effective. As the in- 

 sect is powerless of itself to extend its sphere of infestation from its 

 own immediate habitat, and as the fruit is infested directly from the 

 tree, it follows that the destruction of the scale on the tree removes 

 simultaneously the danger to the tree and that to the fruit. This 



Fig. 79. Oyster-shell scale. (Courtesy of 

 Ohio Agricultural Experiment Station) 



