80 



INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



Food Plants. — The apple is the favorite food of this insect, though 

 it also feeds quite extensively upon the roots of pear trees. The old 

 limbs, young shoots, suckers and roots are attacked. Characteristic 

 knots are produced upon the shoots and others somewhat different upon 

 the roots. Upon the older limbs great rough enlargements appear, 

 which become nearly a foot in diameter and look considerably like a 

 burl. In these many of the lice spend the winter. 



There is considerable difference in the attacks upon the varieties of 

 the apple. The Northern Spy is practically immune, and for this 

 reason is much sought after as a resistant root-stock for grafting pur- 

 poses. Vigorous growing varieties, such as the Rhode Island Greening 

 and Bellflower, are very much injured. In some sections the former is 

 decidedly undesirable because of the great injury thus received. Prac- 

 tically all other commercial varieties are affected in a greater or less 

 degree, the King of Tompkins County being injured the least in the 

 north. 



In a large number of localities throughout the State Mr. G. P. Weldon 

 has found the roots of the pear also seriously infested. 



Natural Enemies.— Several insects prey on the woolly apple aphis, 

 but are not an economic factor in the control of this pest. 



THE ARBORVIT^ PLANT LOUSE 52 



Lachnus thujafalinus Del Guercio 



(Fig. 62) 



Description. — The adults of this louse are amber-brown with the 

 dorsum partially covered with fine whitish powder, definitely arranged 



as shown in Fig. 62. The antennae, 

 legs and cornicles are marked with 

 black. The winged forms have dark 

 head and thorax. In the apterous 

 forms, especially, the head is very 

 narrow and the body widest across 

 the abdomen. The entire surface is 

 covered with quite long, fine hairs. 



Distribution. — The distribution is 

 quite wide and the insect may be 

 found almost anywhere the host plant 



Fig. 62.— The arborvitse plant louse, OCCUrs throughout the State. 

 Lachnus thv jafalinus Del Guercio. En- ■p~„j tji«^+ mi, n' a j i 



larged live times. (Author's illustra- Foo <I Plant. — The cultivated arbor- 



tion, p. c. Jr. Ent.) vit-e {Thuya occidentalis) is the only 



recorded host. The lice feed on the bark of the branches. 



"In the author's previous writings this species has been referred to as the juniper 

 louse, Lachnus juniperi De Geer. 



