Biology and Management of Root-Feeding Beetles (Coleoptera: Curculionidae) in North American Conifer Forests and Plantations

Abstract

Root-feeding beetles, including several species of Hylastes Erichson (Coleoptera: Curculionidae), Hylurgops LeConte (Coleoptera: Curculionidae), Hylobius Gemar (Coleoptera: Curculionidae), Pachylobius LeConte (Coleoptera: Curculionidae), Pissodes Germar (Coleoptera: Curculionidae), and Steremnius Schönherr (Coleoptera: Curculionidae), have emerged as serious problems in conifer plantations and forests in the United States and Canada in recent decades. Root-feeding beetles are particularly associated with stressed, diseased, or injured trees. Emerging adults kill seedlings by girdling them at the root collar and kill older trees, at least in the North and West, by transmitting fungal root pathogens in the genus Leptographium Lagerberg & Melin (Ophiostomatales: Ophiostomataceae). In the South seedling, mortality can be as high as 60% for seedlings planted in winter following fall harvest. For stands harvested after 1 July, planting should be delayed a full year. Broadcast insecticides can be used, but dipping seedlings in 0.75% permethrin prior to planting and physical barriers to feeding have proven effective. However, an integrated pest management approach that emphasizes a combination of measures to minimize attraction of beetles and to maintain health of host trees is recommended. Shelterwood harvest and soil scarification can create site conditions that minimize attraction of root beetles. Precommercial thinning and prescribed fire are often used to reduce tree competition and reduce vulnerability to stem-colonizing bark beetles. However, root beetles are attracted to thinned or burned stands, for at least 6-7 mo. Therefore, thinning should be avoided in areas of high risk for root disease transmission or, when necessary, thinning should be implemented during June or July following beetle dispersal in May. Semiochemicals can be used to monitor abundances of root beetles.

Beetles as Plant Pathogen Vectors

“…Hylastes macer (Schowalter, 2018) Hylastes nigrinus (Schowalter, 2018) Steremnius carinatus (Witcosky et al, 1986) Pissodes fasciatus (Witcosky et al, 1986) Dendroctonus ponderosae (Amman, 1983) Ips pini (Amman, 1983) Ips acuminatus (Amman, 1983) Tomicus spp. (Pan et al, 2018) Tomicus yunnanensis (Lu, 2011) Tomicus minor (Lu, 2011) Tomicus brevipilosus (Amman, 1983;Lu, 2011) Curculionidae Elm tree Scolytus multistriatus (Faccoli and Battisti, 1997) Scolytus scolytus (Webber, 1990) Scolytus pygmaeus (Faccoli and Battisti, 1997) Scolytus triarmatus (Faccoli and Battisti, 1997) Hylurgopinus rufipes (Willsey et al, 2017) Curculionidae…”

“…Fungal conidia are produced in sticky masses (conidial droplets) at the apex of stalked conidiophores, inside the galleries created by the bark beetle. Two pests of the Curculionidae family Hylastes macer and Hylastes nigrinus (Table 1), are the most important vectors of L. wageneri in Douglas-fir and ponderosa pine plantations in the western United States (Schowalter, 2018). In the pines tree, L. wageneri is spread by H. nigrinus and by several long-snouted weevils of the Curculionidae family: e.g., Steremnius carinatus, Pissodes fasciatus (Curculionidae; Table 1).…”

Pest survey card on Pissodes cibriani, P. fasciatus, P. nemorensis, P. nitidus, P. punctatus, P. strobi, P. terminalis, P. yunnanensis and P. zitacuarense

“… The pupal cell (i.e. cocoon) is covered with shredded wood fibre and has a structure that is typical for Pissodes (Schowalter, 2018). When terminals are attacked or when the bark is too thin, the pupal cell is excavated in the sapwood (Figure 3).…”