October, ’20] 
BURKE: PACIFIC OAK TWIG-GIRDLER 
381 
durata), canyon live oak (Q. chrysolepis), engelmann or mesa oak 
(Q. engelmanni), California black oak (Q. calif or nica) and the tan oak 
(Q. densiflora). 
The species range from a few feet above sea level to an altitude of 
6,000 feet. 
Characteristic Work 
The first indication of an attack by the twig-girdler is scattering 
small patches of fading foliage. Other insects and diseases cause 
somewhat similar dying branches, but the trained eye usually can detect 
the difference. Roundheaded borers kill larger branches and their 
work is not so common, scales of the genus Kermes and some of the 
gall wasps kill smaller twigs, and a disease supposed to be related to 
the chestnut blight kills large patches of foliage on adjoining branches. 
Childs says that the foliage that dies from the girdler work is a light 
straw color when dry, while that killed by the disease is a distinctive 
reddish brown tinge. These color differences may hold true in some 
cases, especially during the first year, but the girdler work of the sec¬ 
ond year is apt to cause good sized patches of reddish foliage which are 
difficult to distinguish from the disease work. 
A close examination of the dying or dead twigs will always show the 
real cause of the trouble. If it is the girdler there will be a small 
mine winding around under the bark and down the twig. During the 
first year this only goes a few inches, but during the second it may go 
for a foot or more, sometimes two feet, the mine spiralling the branch 
and killing all of the twigs terminal to it. It may go down one fork 
and up another. The foliage on the killed twigs will vary from a fad¬ 
ing green to a reddish brown, depending on the time of the year each 
was killed. Usually most of the mine is just under the bark, but it 
may go into the wood. It usually spirals around the branch from four 
to twelve times, but sometimes runs straight down for a long distance. 
Just before it is completed the mine usually reverses and runs back up 
the branch for an inch or more, where it goes into the wood and ter¬ 
minates in the slightly enlarged pupal cell. After the beetle emerges 
the pupal cell opens on the surface of the branch in the oval emergence 
hole. Most of the branches killed by the girdler are not over one half 
an inch in diameter. The leaves fall before the end of the second year 
and the work shows as a leafless branch, an unsightly blemish on a 
splendid object of natural beauty. 
The Twig-Girdler 
The twig-girdler is a slender, whitish flattened boring grub of the 
common agriloid type. It varies in length from 1 mm. when newly 
hatched to 18 mm. when full grown. The mouth parts and tail for- 
