280 OHIO EXPERIMENT STATION: BULLETIN 332 



SCALE AND OTHER SUCKING INSECTS 



The group of insects to be discussed in the following pages is, 

 as a class, inconspicuous in appearance but among them are some 

 of the worst known pests of shade and forest trees. Because of 

 their unobtrusiveness it frequently follows that plants become 

 infested and seriously injured before the depredator is known to be 

 present. 



As a whole the insects of this group and particularly the scale 

 insects are more destructive under urban than rural conditions. 

 Several reasons may be given for this fact : In the first place, most 

 scales seem to thrive best upon hosts with weakened constitutions, 

 and the adverse conditions attending plant growth in cities and 

 villages tend to promote this; second, abundant opportunity exists 

 for introduction and distribution through the constant transference 

 of planting stock ; third and final, a wide range of hosts is available 

 so that the various insects, and particularly those having cosmo- 

 politan feeding habits, are not hampered by lack of suitable food. 



THE SAN JOSE SCALE 



Aspidiotus perniciosus Comst.) 



The San Jose scale is the most destructive scale insect of fruit 

 trees in the State and causes severe injury to some ornamentals. 

 It cannot, however, be classed as a pest of general importance on 

 forest and shade trees. Some few species, nevertheless, are at- 

 tacked with considerable severity, such as osage orange, sometimes 

 used in plantings for post timber. For this reason, and also because 

 some ornamentals are injured, a discussion in a publication of this 

 kind appears necessary. 



Description. — The trunk, limbs and branches of a tree, badly 

 infested with San Jose scale have a characteristic gray, ashy appear- 

 ance ; and, if a knife blade is drawn over an area plastered with the 

 insects, a yellow, oily juice is crushed out. 



Individually, the full-grown female scales are flat, circular, 

 about one-twelfth of an inch in diameter, and with a slightly raised 

 central area, or nipple, which is dark or yellow. (See Plate XLVII, 

 Fig. 1.) The body of the female is without eyes, legs or antennae, 

 is slightly oval, light yellow in color and is somewhat smaller than 

 the scale covering. 



The male scale is smaller that that of the female, is about twice 

 as long as broad and is black in color. The male insect is a fragile, 

 pink, winged creature which flies readily during calm weather. The 

 young insects are minute, bright yellow, louse-like creatures which 

 for the most part are born alive, though occasionally the mother 



