Seasonal Emergence, Egg Gallery Characteristics, and Natural Enemies of the Eastern Ash Bark Beetle, Hylesinus aculeatus (Coleoptera: Curculionidae: Scolytinae), in Michigan

Hylesinus aculeatus Say (Coleoptera: Curculionidae: Scolytinae) commonly infests the trunks and limbs of recently dead, dying, or cut ash (Fraxinus spp.) trees in eastern North America. In the Great Lakes region, H. aculeatus is univoltine, overwinters as adults, breeds in late spring and early summer, and constructs transverse biramous egg galleries. I sampled trunk and branch sections from three small-diameter white ash (F. americana L.) trees that were cut in April 1986 in Ingham County, Michigan, and then naturally infested by H. aculeatus and associates. Bolts cut from these trees and placed in an outdoor rearing cage in late June 1986 yielded H. aculeatus brood adults, adults of three hymenopteran braconid parasitoids [Coeloides scolytivorus (Cresson), Dendrosoter sp. and Spathius sp.], and one predatory clerid beetle [Enoclerus nigripes (Say)]. Hylesinus aculeatus brood adult emergence began in July, peaked in early August, and ended in early October. Of 590 egg galleries measured on bolts collected from the study trees in autumn 1986, 4% had one arm and 96% had two arms (biramous). On average, the biramous egg galleries measured 36 mm long and had 32 egg niches and 23 larval mines each. Average nearest-neighbor distance between entrance tunnels was 29 mm. For bolts that had retained all their original bark, survival from egg (= number of egg niches) to adult (= number of H. aculeatus exit holes) averaged 52.7%. Mean percent parasitism was estimated at 2.4%.