October, ’20] 
BURKE: PACIFIC OAK TWIG-GIRDLER 
383 
her eggs and both soon die. So far as could be determined, most of the 
beetles live about two weeks. 
The Egg. When first laid the egg is a dull white, flattened oval 
scale-like object 1} mm. long and f mm. broad. It soon becomes 
darker with age and development and in from 4 to 5 days turns a shiny 
black. It is covered with a varnish-like covering which catches the 
dust, etc., so that in a week or more it looks like the brownish or black¬ 
ish gray bark of the twigs. The egg is laid singly on the bark of the 
twig, near the end of the last year’s growth. It is not tucked under a 
loose flake of the bark, or in a crevice, but is laid on the smooth bark, 
usually near the base of a small twig or a leaf scar. In the great 
majority of cases only a single egg is laid on a twig, but in a few cases 
two were observed close together and in one or two instances three 
were laid scatteringly along the stem. In hatching, the young larva 
bores into the bark through the bottom of the shell and packs the shell 
full of the borings. Most of the eggs are laid during the last of June 
and the first of July. All appear to hatch in from two to three weeks 
after they have been laid. 
Number of Generations 
The oak twig-girdler is a two-year species. Eggs laid in June of 
1912, 1914 and 1916 produced beetles in 1914, 1916 and 1918. In 
many localities there is no brood of beetles during the alternate years. 
In some there are a few scattering individuals and in others there is a 
well-defined brood each year; that is, in June, beetles will be emerging 
from some twigs while year-old larvae will be found in others; in Jan¬ 
uary, eighteen-months old larvae will be found in the large twigs and 
six-months old larvae in the small ones. A most interesting occurrence 
was observed at Confidence, Tuolumne County, during August, 1919. 
All of the specimens found in the black oak were small larvae from eggs 
laid in June, 1919, while all of those found in the canyon live oak were 
year-old larvae from eggs laid in June, 1918. 
Natural Enemies 
Natural enemies undoubtedly play an important part in the life 
history of the twig-girdler. Nine species of Hymenopterous parasites 
were reared from the larval mines and pupal cells. One of these was a 
new species and new genus, and three others were new species. Messrs. 
S. A. Rohwer and R. A. Cushman identified the species and named 
the new ones. 
Cryptohelcostizus rufigaster Cushman, 1 n. gen., n. sp., was reared 
several times from a single larva or cocoon found in the pupal cell of 
the girdler. Two Cryptoideus fasciatus Ashm. were reared from sim- 
1 Cushman, R. A., Proc., U. S. Nat. Mus., Vol. 55, pp. 534-35. 
