hornbeam. Details on the immature forms and biology of these and other species of 
Acrobasis are available (921, 922). 
The genus Dioryctria has Holarctic distribution, and the larvae of all species are 
borers in conifers. Many are highly injurious to seeds and cones (360, 547). The 
larval habits of some of the more widely distributed species are quite variable. This 
suggests that more than one species is involved in certain cases. This can be 
established only through further taxonomic and biological investigations. The 
genus has been discussed (357, 360, 553, 897, 901, 902, 924, 925). 
The Zimmermann pine moth, D. zimmermanni (Grote), is widely distributed in 
the Northern United States and southern Canada. The larvae feed in the cambial 
region and outer xylem under the bark of limbs and trunks of all commonly grown 
species of pines. The adult has forewings of gray blended with red-brown and 
marked with transverse zigzag whitish and black lines: the hindwings are yellowish 
white. Mature larvae are variably dirty-white, pink to greenish, with prominent 
small black setal bases, with black muscle attachments: they are about 18 mm long. 
Adults emerge from mid-July to mid-August and deposit their eggs at the edges 
of wounds, on resin masses, in bark crevices. or on terminal buds. Hatching occurs 
in about 8 to 10 days and the young larvae, without feeding. enter bark recesses and 
spin hibernacula. Here they remain until the following spring. Feeding begins in 
May or June, first in the bark, then by tunneling in the cambium area of new growth 
on terminals or laterals. Damaged terminals usually become “‘fish-hooked™ and 
turn yellowish green. Toward the end of June, the larvae leave the new growth and 
tunnel beneath the bark in the whorl area, girdling branches and leaders. Pupation 
occurs in resin masses or in the tunnel. Dead tops, dead branches hanging on trees 
(fig. 70), and burllike growths on trunks above girdled whorls and pitch masses 
(fig. 71) are evidence of attack. Infested trees tend to be attacked again and again, 
thus becoming so-called brood trees (/0/7). 
F-49295 F-492960 
Figure 70.—Damage to young pine by Figure 71.—Burllike growths on trunk 
the Zimmermann pine moth, above girdled whorl, a sign of attack 
Dioryctria Zimmermanni. by Zimmermann pine moth. 
182 
