ENGLISH: ILLINOIS TREES: THEIR INSECT ENEMIES 53 



Control. In some species of leaf miners, the larvae drop to 

 the ground with the leaves in the fall; these larvae may be de- 

 stroyed if the leaves are burned. Until late years no insecticide 

 for the control of leaf miners has been available. Recent work 

 shows that Control Measure 14 or 15 (end of circular) is ef- 

 fective against some species. 



Gall-Producing Insects, fig. 38. — Galls appear on oak twigs 

 in a variety of sizes and shapes that include irregular, bumpy, 

 warty growths and smooth, attractive, spherical formations. 

 These galls are not manifestations of a systemic disease and are 

 no cause for alarm. One of the unattractive kinds, the gouty oak 

 gall, fig. 38A, most often found on red oak, is produced by a small 

 wasp belonging to the family Cynipidae. Individual cells, each 

 inhabited by a larva of the wasp, make up the inside of the gall. 



A woolly ball an inch or more in diameter, at first white but 

 brown when older, is known as the wool sower gall, fig. 385. 

 Also produced by Cynipidae, this gall is not numerous enough to 

 cause severe damage. The oak apple, fig. 38C, is another spheri- 

 cal gall, green or brown in color, an inch or more in diameter, 

 which sometimes occurs in clusters. The spongy mass inside 

 each gall has a larval cell. 



Control. Damage to oaks by galls is rarely serious enough 

 to justify spraying. Since galls provide protection for the insects 

 inside, sprays applied after the galls develop are ineffective. 



PINE 



Sawflies, Neodiprion spp., fig. 39. — The larvae of sawflies 

 are often seen as colonies of caterpillars feeding on pine needles. 

 They are especially injurious to young pines, which may be killed 

 by one defoliation. Each larva, about an inch long when grown, 

 has a red, brown, or black head, and many larvae have rows of 

 spots running lengthwise of their bodies. The insect overwinters 

 in a brown pupal case in the debris under a tree. Each less than 

 half an inch long, the seldom-seen, beelike adults emerge in the 

 spring. The female deposits eggs in slits she makes in pine nee- 

 dles. Although hard to see when first hatched, because of their 

 small size, the sawfly larvae soon attract attention by the disap- 

 pearance of needles required to meet their appetites. Sawflies 

 may produce two generations a year. 



Control Measure 2 (end of circular) . 



