Breeding attacks begin in material that is weakened by drought, disease, .or 
injury. The bark of any wood recently cut from a living elm may be colonized. 
Attacks may quickly spread to undiseased parts of the tree and to adjacent healthy 
elms. Rapid death of entire trees or sections of trees and the retention of shriveled 
brown leaves indicate mass attack and successful colonization by the beetles, 
although beetles may also colonize material after leaves have wilted and been shed. 
Trees that are vigorously attacked emanate a sticky liquid that attracts ants, yellow 
jackets, and certain moths. Bark that has been removed or dried to the point of 
cracking will not be infested. Females initiate attack and release an aggregating 
pheromone that attracts both sexes to the breeding site. After mating near the 
entrance of their attacking tunnels, females bore egg galleries 2.5 to 8 cm long. 
engraving the surface of the wood, parallel with the grain (fig. 165B). Eggs are 
deposited in niches along the sides of the gallery. The larvae feed in the inner bark 
and the surface of the wood, angling away from the gallery. When fully grown, they 
form cells in which to pupate in the bark. During the spring and summer, the life 
cycle may be completed in 35 to 40 days. The spring-flying adults produce a 
generation that emerges from mid-June to mid-August, depending upon the lati- 
tude. Most of the progeny of the summer-flying adults enter a developmental 
diapause and overwinter, but a portion continues to develop and emerges in the fall. 
The vertical orientation, the unbranched condition, and the engraving of the 
sapwood by both adults and larvae distinguish the gallery system of this species 
from the branched horizontal galleries of the native elm bark beetle. 
Because of its role in the transmission of Dutch elm disease, the smaller 
European elm bark beetle has been the subject of considerable research, and huge 
expenditures have been made to eradicate or control it. Eradication efforts proved 
futile, but progress has been made on its control. The fundamental mode of 
controlling the size of the elm bark beetle population is limiting their supply of 
breeding material (/287). Elm firewood, broken limbs, and severely stressed trees 
as well as elms that have Dutch elm disease should be eliminated or treated with an 
insecticide. In addition to the physical removal and burning or burying of infested 
or potential beetle breeding material (sanitation), diseased or unwanted elms can be 
rendered unsuitable for beetle breeding by the trap tree technique based upon 
injection of certain herbicides that cause the bark to dry before larvae are fully 
developed (943). 
Beetles that escape sanitation can be lured away from elms and killed on sticky 
traps baited with a synthetic copy of their aggregation pheromone (7/6, 977). 
An integrated approach that employs a medley of techniques to manage the elm, 
the bark beetles, and the fungus is most effective in reducing losses to Dutch elm 
disease. 
Further information on control of elm bark beetles and Dutch elm disease is 
available (688, 7/5, 717, 718). 
The larger shothole borer, S. mali (Bechstein), also introduced from Europe, 
has been recorded from southern Ontario and Quebec in Canada, and from Con- 
necticut, Maryland, New York, New Jersey, Ohio, Indiana, and Pennsylvania. It 
breeds in moribund apple, cherry, and elm. During its dispersal phase it sometimes 
feeds in twig crotches of healthy trees and may be an occasional vector of Dutch 
elm disease. The very dark-brown adult is from 3.4 to 4.4 mm long, and is about 
one-half as wide as long. The elytra have the punctures arranged in regular strial 
and interstrial rows of nearly equal size. The abdomen is weakly concave ventrally. 
The fifth sternite is longer than the third and fourth combined and the elevation of 
354 
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