416 Annals Entomological Society of America [Vol. IX, 



sufficient water, the damage from the scales is much more 

 noticeable. It is rarely that trees are actually killed by its 

 attacks. 



It is not an easy matter to estimate the amount of damage 

 b}^ such a pest, even when it occurs in such countless numbers as 

 on the Monterey pines at Stanford University. The amount of 

 damage may be estimated by determining the per cent of leaf 

 tissue which has lost its chlorophyll by the sucking and the 

 additional percent of leaf tissue lost by the death of the needles 

 long before their normal time for dying. Our records for 

 Piniis radiata in the Stanford arboretum indicate that approx- 

 imately five per cent of leaf tissue is destroyed in these two ways 

 by Chionaspis pinifolice, Fitch. This injury, together with that 

 caused by the other pests of the Monterey pine, such as Diplosis 

 pini-radiatce Snow and Physokermes insignicola Craw so weaken 

 the trees that they fall an easy prey to the Scolytid beetles. 



A morphological study of a normal Monterey pine leaf shows 

 its structure to be as follows: On the outside is the epidermis, 

 a single layer of cells through which the stomata, or breathing 

 pores, pass to the tissues underneath. Under the epidermis 

 is the schlerenchyma, a strengthening tissue made up of several 

 layers of heavy-walled cells. Next is the mesophyll with 

 characteristically infolded outer walls, the cells of which contain 

 the chlorophyll granules. There are two resin ducts, one located 

 at a point inside each angle made at the union of the rounded 

 and flat surfaces of the leaf. The resin ducts are surrounded 

 by a double row of resin-secreting cells. Inside the mesophyll 

 is the bundle sheath surrounding the stele with its two parallel 

 vascular bundles. All the tissues described above are shown 

 in Photomicrograph No. II. 



Examination of the photomicrographs II and III will show 

 what the insect does to the plant. The four sucking and piercing 

 setae of the coccid, which are the modified mouthparts of this 

 family, enter the needle either by spreading apart the epidermal 

 cells or at an open stoma. Photograph III shows that schler- 

 enchymatous cells have been bored through. The appearance 

 of the cells around the setae indicates that this insect, in conimon 

 with some other members of the family and the Aphididce, uses 

 saliva to dissolve a passage through the hard walls. This 

 section shows that a sheath has been formed around the setae. 



