Large moncultures of Populus spp. grown for pulp, non-structural timber, or biofuels are commonly attacked by Chrysomela scripta. Integrated pest management (IPM) professionals in the Pacific Northwest (PNW) need to be able to identify leaf beetle damage, prepare a monitoring program, and develop a management protocol to prevent or remedy an outbreak of this pest.
Chrysomeloidea is a superfamily with four families, one of which is Chrysomelidae, the leaf beetles. The genus Chrysomela identified by Linnaeus, was further divided into a subgenus Chrysomela (Macrolina). The species name scripta was attributed to Fabricius. Two other Chrysomelidae species attack Salicaceae trees. These include the imported willow leaf beetle, Plagiodera versicolora (Laicharting), introduced into the US in 1915 from Europe and widely distributed in the eastern US and southern Canada. It is sporadically found throughout North America (Riley et al. 2003). The other species is Altica populi, a defoliating leaf beetle found in the US; however, its distribution is unknown (Charles et al. 2014).
Cottonwood leaf beetle hosts include poplar, willow, aspen, and alders.
Cottonwood leaf beetles are common from southeastern Alaska, coast to coast throughout the northern states, and south to Florida in the east.
Adults survive the winter under leaf litter or within bark crevices. They become active in April. Gravid females deposit yellowish, oval-shaped eggs in clusters (Figure 1) on leaves. Each female can deposit multiple egg masses during her lifespan. Upon hatching, first instars feed gregariously as they skeletonize the leaf surface. Larvae consume large portions of the leaf in later instars. Eversible larval glands secrete salicylaldehyde as a defensive secretion.
Poplars grown for biofuels retain a large proportion of their biomass as succulent, long-shoot foliage preferred by C. scripta (Coyle et al. 2005). Cottonwood leaf beetle defoliation can reduce tree volume in certain clones by 70% over three growing seasons (Coyle et al. 2002).