Gluphisia septentrionis Walker (Lepidoptera: Notodontidae)
Outbreak populations of the common pebble moth, Gluphisia septentrionis can totally defoliate thousands of hectares of poplar trees (Leininger et al. 2004; Del Pozo-Valdivia 2011). Professional IPM practitioners can use this publication as a guide toward identifying Gluphisia, monitoring the population, and controlling Gluphisia outbreaks in the Pacific Northwest.
Worldwide, many Notodontidae species are major defoliators of poplar trees. Packard (1895) was the first to report G. septentrionis in the Pacific Northwest. He identified three other Gluphisia species; G. lintneri (Grote), G. severa Edwards, and G. avimacula Hudson. He found that these other Gluphisia species also fed on poplar in California and New York (Packard, 1895). Crabo et al. (2016) collected G. severa in coastal rain forest and high mountain forest, and G. avimacula in British Columbia, Canada, where larvae feed on aspen (Populus tremuloides).
Gluphisia septentrionis feeds on Populus species, including P. trichocarpa, P. nigra, P. tremuloides, P. balsamifera, and Populus hybrid species. Other host species include Alnus incana (alder), Betula alleghaniensis (birch), B. papyrifera, Juglans cinerea (butternut), Liquidambar styraciflua (sweetgum), Ulmus americana (elm), Salix (willow), and Tilia (linden or basswood; Robinson et al. 2015).
Gluphisia have been collected throughout the US, from Maine to California and South Carolina to Washington, with the exception of some southeastern states (BAMONA 2011). During the mid-1900s, G. septentrionis was reported to occur only in southeastern Canada and parts of the northeastern US.
Gluphisia septentrionis has been called the “common pebble moth,” because the adult’s resting shape is cryptic. Adults are small, dark, grayish moths with a wingspan of 2.5–3.3 cm. The front wings are rounded gray with irregularly shaped beige and dark gray bands, and the hind wings are light gray (Leininger et al. 2004). Males in laboratory conditions have a short lifespan (6 days) and can mate at least three times (Smedley and Eisner 1996). The eggs are small and flattened at the bottom (Stehr 2005). Descriptions of the last instar larva indicates that it is a pale green caterpillar, 3.3–3.8 cm long with small, reddish, transversal stripes dorsally (Leininger et al. 2004; Wagner 2005). Gluphisia possess a classic noctuid pupa (Figure 1) slightly flatted dorsally and ventrally (Miller 1992).
Del Pozo-Valdivia (2011) researched G. septentrionis’ life cycle (Figure 1). This moth flies in some regions of Canada and the Pacific Northwest from early May through June, and also from July through August (Scott 2011). Those two flight periods can be represented with data from the University of Alberta E.H. Strickland Entomological Museum (Anweiler n.d.). Leininger et al. (2004) indicates that G. septentrionis may have two generations per year in Louisiana, with a large adult emergence in June. Gluphisia can develop from an egg to an adult in 28 to 37 days, allowing for a second flight of adults in mid-summer. This second generation of Gluphisia pupates in September and October and overwinters as a pupa (Stehr 2005).