210 



MONTANA EXPERIMENT STATION. 



from under the protecting cover of the parent scale they crawl to 

 other parts of the twigs, principally to the young shoots which at 

 that time of year are tender and succulent. In rare cases they settle 

 on the fruit of the apple and pear. 



After settling down and inserting into the bark the long thread- 

 like hairs through which the juices of the plant are extracted, the 



Figure 2. — Oyster-shell Bark-louse- a, female scale from below 

 showing eggs; b, same from above, greatly enlarged; c, female 

 scales; d, male scales enlarged; e, male scales natural size. 

 (Howard, Yearbook, U. S. Dept. of Agr.) 



insect goes through remarkable changes. From pores in the back, 

 principally at the hinder part of the body, a glandular secretion ap- 

 pears, and from it the scale is formed. The female molts or casts the 

 outer skin twice and the male once. The cast skins are incorporated 

 in the scales (See Fig. 2, b). After molting both sexes continue to 

 grow, the female attaining a much larger size than the male ; com- 



