Ips Engraver Beetles

Pine bark beetles are frequent pests of stressed pines (Pinus spp.) in the southern United States. The five most common southern pine bark beetle species include three in the genus Ips (the six-spined engraver, I. calligraphus (Germar); the southern pine engraver, I. grandicollis (Eichhoff); and the small southern pine engraver, I. avulsus (Eichhoff)) (Fig. 1), and two species of Dendroctonus (the southern pine beetle, D. frontalis Zimmermann, and the black turpentine beetle, D. terebrans (Olivier)). Like other pine bark beetles, Ips pine engravers live predominantly in the inner bark, where they breed and feed on phloem tissue. Pines successfully colonized by Ips engravers, if not already dead, are killed by adult and larval feeding in the phloem (which can girdle the tree) and by colonization of the sapwood with blue-stain fungi that the beetles introduce. The blue-stain fungi spread into the xylem and block water flow, serving to hasten tree mortality (Connor and Wilkinson 1983, Kopper et al. 2004).

Ips beetles usually colonize only those trees that are already stressed, declining, or fallen due to other environmental or biotic factors. Ips also readily colonize cut logs and slash, and are attracted to fresh pine odors. Infestations may occur in response to drought, root injury or disease, timber management activities, lightning strikes, or other stresses, and sometimes occur in association with attacks by D. frontalis or D. terebrans (Anderson and Anderson 1968, Lovelady et al. 1991, Miller 1983). When populations of Ips beetles are sufficiently high, they can overcome the defenses of apparently healthy trees by attacking in large numbers. Ips outbreaks, however, are greatly limited in duration and spatial scale compared to outbreaks of the more aggressive D. frontalis (Anderson 1977).