Biology of Dendroctonus punctatus (Coleoptera: Scolytidae)

Abstract

The biology of Dendroctonus punctatus LeConte was studied in white spruce, Picea glauca (Moench) Voss, forests of boreal western North America and in the laboratory. Engelmann spruce, P. engelmannii (Parry) Engelmann, was not found to be infested in nature but was used successfully for rearing in the laboratory. Life stages and behavior are described. Mating occurs between siblings before emergence from their host trees. Trees are attacked near ground level, often unsuccessfully and typically at low density (4.4 attacks per tree average). Infested trees varied in size but averaged 24.9 cm in diameter and 15 m in height. Ninety-two percent of these trees had deteriorated crowns, stem injuries (presence of resin), or a combination of those two conditions. Egg galleries averaged 6.3 cm long and varied in orientation and shape; most were directed upward at an angle. Eggs were laid in a cluster (78 eggs average) along one side of the egg gallery. After eclosion, larvae fed side by side in a common brood chamber that often extended below ground level. Larvae had four instars. Mature larvae moved throughout frass in the brood chamber and pupated in separate cells. When transformed to adults, they tunneled actively throughout the brood chamber, enlarging it and scoring the sapvvood by their feeding. They emerged through ruptures in the weakened bark. Observations indicate that one generation per year occurs in nature, but broods that originate in late summer may possibly overwinter twice. Offspring of overwintered adults reached the adult stage in the laboratory (17-22°C) in as few as 46 d. Commensal and predacious organisms are listed. Dendroctonus rufipennis (Kirby) and Ips spp. also infested spruce trees in the study area but did not occur in trees with D. punctatus.