FIELD ENTOMOLOGIST. 9 
The peach twig-borer is one of the most important pests to the 
peach growers of Western Colorado. All of the peach spraying car¬ 
ried on in the Grand Valley the past spring was directed against either 
the peach aphis or the peach twig-borer. 
It is estimated that this pest cost the peach growers of California 
over a million dollars in the four years following 1898. To the grow¬ 
ers of Grand Valley it has cost much loss for some years past, and its 
distribution on the Western Slope of the state seems to be quite gen¬ 
eral wherever peaches are grown. 
Life History and Injury —The injury is caused by a small pinkish 
brown worm, with black head, measuring, when fully grown, about 
one-half inch long. The worm is the larval or immature stage of a 
small greyish moth. 
The winter is passed by the larvae, still very minute, in small 
chambers hollowed out within the spongy tissue of the bark at the 
crotches of small limbs. The chamber is lined with silk of the larva’s 
secretion, and the only evidence of the presence of the chamber is in 
a very small and inconspicuous heap of frass or peach-wood dust 
standing outward from the mouth of the burrow. Early in the spring, 
at about the same time the foliage of the peach show 1 ? as small green 
tufts upon the twig tips, the larvae leave their burrows and attack 
the. tender twigs, boring into them near their tips and down through 
their pitch, forming galleries from one-third to one and one-half inch 
in length. 
Examinations of infested peach trees at Palisade last spring 
showed these bored twigs wilting and. turning brown early in the 
month of May. Later in the season, twigs bearing half a dozen leaf 
tufts near their tips would have each bored and killed and from all 
appearances by the same larvae. This injury to the terminal twigs 
constitute an important injury to the tree. Young peach trees are 
usually worst infested, their growth being sometimes greatly retarded. 
On the 18th of May a number of larvae were taken in peach 
twigs at Palisade and kept in water in a closed cage at my insectary. 
An examination of the cage May 24 showed that two of the larvae 
had already changed to brown chrysalids or pupae, both emerging 
on May 28. 
On May 20 many larvae were also found concealed about the 
base of the tree at the surface of the earth and hiding about the 
bark, and it seems that at this date the majority of the larvae, which 
hibernated over winter in the small bark cavities, have now completed 
their feeding on the twigs and are descending for pupation. As 
stated, the usual habit of the first or hibernating brood of larvae is to 
burrow into the twigs. A few instances were "found, however, where 
small peaches, still no larger than a pea, were burrowed into, leaving 
the fruit with a hollow cavity within. 
The small second generation worms were seen beginning their 
work early in June. It is this generation which brings about another 
and by far the greater amount of injury to the peach crop. Larvae 
from this generation make their way directly into the forming peach 
