pushes its granular frass to the outside and through which the 
adult eventually emerges. There is one generation per year (280). 
During the past several years, the locust borer has destroyed 
thousands of acres of natural regeneration and plantations of 
black locust. Enormous numbers of older trees, especially slowly 
growing overtopped trees, have also been badly damaged or killed. 
On the other hand, thrifty dominant trees over 10 years old have 
seldom been killed. Infested trees are physically weakened by the 
larval tunnels, the smaller ones often being restricted to shrub 
form by repeated attacks (fig. 53B). Trees growing on poor sites 
are especially susceptible to attack and suffer serious damage 
during periods of prolonged drought. 
F-501514, 501515 
FIGURE 538.—Damage caused 
by the locust borer, Mega- 
cyllene robiniae: A, larval 
damage in heartwood; B, 
damage to small trees. 
