The genus Hylesinus contains a number of species that breed by preference in 
various species of ash, and are commonly known as ash bark beetles. The adults 
differ from most other bark beetles in having variegated coloration produced by 
bands or spots of light-colored scales alternating with areas of dark scales. The 
body is rather stout, and the elytra gradually descend behind; the antenna has a 
seven-jointed funicle, with the club elongate, fusiform, and compressed. Favorite 
breeding material consists of recently cut or broken trees; however, living trees 
weakened by mechanical injury, disease, or fire may be attacked. Parasites and 
predators, especially the braconid, Coeloides scolytivorus (Cresson), and the clerid, 
Enoclerus nigripes (Say), provide a considerable degree of control at times. 
Hylesinus aculeatus (Say), the eastern ash bark beetle, is the most common 
eastern species. It breeds in ash species throughout the eastern part of the United 
States and southeastern Canada. The adult is grayish brown with nearly black 
markings and is 2 to 3 mm long. Winter is spent in the adult stage in tunnels in the 
bark of living or felled trees. The adults emerge in the spring and fly to the trunks or 
limbs of recently felled, dying, or seriously weakened trees to breed. Egg galleries 
are constructed between the bark and wood, both of which are deeply engraved. 
The galleries are biramous and transverse, with the two arms connected by a short 
tunnel or nuptial chamber just below the entrance hole (fig. 157). Eggs are laid in 
niches along the sides of the gallery. The larvae feed away from the gallery, 
following the grain. Pupation occurs in deep oval cells between the bark and wood. 
There are one to three generations per year, depending on location. This species and 
the slightly larger H. pruinosus (Eichhoff) are economic pests to producers of rustic 
ash products; otherwise, these beetles cause little or no economic damage. 
7 
Courtesy Duke Univ. Sch. For. 
Figure 157.—Transverse egg galleries and vertical larval 
tunnels of Hylesinus aculeatus, the eastern ash bark 
beetle, in white ash. 
34] 
