INSECT ENEMIES OF WESTERN FORESTS 53 



Key to the Recognition of Some Important Insect Galls 



A. Galls formed on coniferous trees. 



1. Galls affecting pine needles. 



a. Needles greatly enlarged or swollen at the base 



gall midges, page 53. 

 &. Needles blistered within the sheaths, causing pre- 

 mature shedding pine needle mite, page 52. 



2. Twigs with dying and dead needle tufts ; bark filled with res- 



inous pockets containing small red maggots 



pitch midges, page 54 



3. Swollen twigs of western white pine covered with gray, cot- 



tony secretion woolly pine louse, page 48. 



4. Cone-shaped galls on terminal twigs of spruce 



spruce gall bark lice, page 47. 



5. Prickly, burrlike or conical galls on juniper gall midges, page 53. 



B. Galls formed on broadleaved trees. 



1. Galls inhabited by small, white, legless, apparently headless 



larvae cynipid wasps, page 53. 



2. Galls inhabited by small pink or red maggots gall midges, page 53. 



3. Galls inhabited by small bugs with cottony wax secretions 



gall aphids, page 47. 



4. Galls inhabited by microscopic eight-legged mites 



gall mites, page 52. 



Gallflies or Cynipid Wasps 



(Cynipidae) 



One group of small, four-winged, usually somber-colored yellow to 

 brown or black, antlike wasps are responsible for the formation of a 

 great variety of galls on the different parts of various forest trees, 

 but particuarly on the oaks. These galls may be large, round, and 

 shiny, like the common oak apples, or very irregular in sha^^e and 

 spiny, or may consist of just a tiny swelling on leaf, twig, or root. 

 The larvae that inhabit these galls are white, legless, and without 

 a distinct head. There are over 200 species described from various 

 plants in the Western States. Only a few, however, do any appre- 

 ciable damage. 



Gall Midges 



The gall midges belonging to the family Cecidomyiidae are re- 

 sponsible for the formation of a great variety of small galls on many 

 different forest trees and plants. The adults are tiny pink flies re- 

 sembling mosquitoes and are called midges. The larvae are small 

 pink or red maggots, without legs or definite head, but with a dark 

 "breastbone." Almost any part of the tree may be affected, but most 

 galls are formed on the needles or leaves, in the cones or seeds, or in 

 the bark of twigs. A few species on forest trees are of some economic 

 importance. 



The Monterey pine midge {Thecodiplosw pini-radiatae S. and M.) 

 works at the base of the newly formed needles of Monterey pine in 

 central California and causes them to become swollen and shortened 

 (fig. 24). Sometimes heavily infested twigs are killed and the orna- 

 mental value of the trees seriously impaired. Other species that 

 produce swellings at the base of needles on pines include Janetiella 

 coloradensis Felt on pines in Colorado and Utah, and Thecodiplosis 

 cocherelli Felt on Pinus edulis in Colorado. 



