INSECTS AND INSECTICIDES. 
17 
could be killed at one application. These insecticides were 
applied on July 26th, August 3rd, 11th and 21st. The helle¬ 
bore seemed to be far less effective than the other two reme¬ 
dies. We consider this the most dangerous insect with 
which we have had to contend for years. There are prob¬ 
ably two or three broods annually, and it passes the winter 
as a perfect insect, hence it would be desirable to burn all 
weeds and tops of vegetables, so as to afford them as few hid¬ 
ing places as possible. 
FOREST TREE INSECTS. 
The cottonwoods are defoliated annually by the larva of 
the cottonwood beetle ( Plagiodera scripta ), but are held in 
check by the common blackbird. 
Several species of Pemphigus cause galls to form on the 
stems and leaves of the species of cottonwood. The poplar 
gall louse wanders in immense numbers up and down the 
stems and trunks of the smooth bark cottonwood in fall. 
In Southern Colorado the poplar borer ( Saperda calcarata ) 
is injurious to Populus angulatus and the Lombardy poplar. 
The larva of the moth Tortrix roseana is a general 
feeder, but works particularly on the young leaves of the 
apple in May. 
The box elder is defoliated annually by the leaf-rolling 
caterpillar ( Caccecia senifera). The larva is green with two 
longitudinal white stripes. The blackbird feeds on them in 
large numbers. 
The elm-leaf caterpillar ( Vanessa antiopa) feeds on the 
elm and willow, and occasionally on the cottonwood. 
The larvae are gregarious while feeding, and present a 
formidable appearance. It is the earliest butterfly to 
appear in spring, being on the wing in favorable weather 
in March. 
Pear-tree slug ( Selandria cerasi ). This insect seems to 
prefer the leaves of the plum; it but rarely attacks the 
cherry or the pear in Colorado. There are two broods 
