Aspen Skeletonizer, Phratora purpurea pururea / Cottonwood leaf beetle, Chrysomela scripta
 

Fig. 300  Aspen skeletonizer larvae and feeding damage.	Fig. 301   Adult cottonwood leaf beetle.	Fig. 302  Cottonwood leaf beetle larva.
Fig. 303  Cottonwood leaf beetle larvae feeding on leaf.	Fig. 304  Cottonwood leaf beetle eggs.

Distribution:  Both leaf beetle species are found throughout B.C. 

TREE SPECIES ATTACKED:  The aspen skeletonizer feeds on aspen, black cottonwood, balsam poplar, hybrid poplars, paper birch, and red alder. The cottonwood leaf beetle attacks black cottonwood, hybrid poplars, and balsam poplar, but not trembling aspen. Both species also attack willow. Other leaf beetle species that feed on broadleaf trees are listed on page 217 of the Field Guide to Forest Damage in B.C..

What To Look For: Skeletonized leaves with intact veins; groups of grublike larvae with well-developed legs on the thorax but no legs on the abdomen.

Insect Description & Damage Symptoms: Mature Phratora larvae are about 0.6 cm long. They are black and have legs on the thorax but not on the abdomen. Larvae are difficult to identify to species. Adults are unspotted, purplish to greenish metallic beetles, 0.4 to 0.5 cm long. Their wing covers have several rows of punctures, which distinguishes them from flea beetles. Mature Chrysomela larvae are about 1.2 cm long and have legs on the thorax but not on the abdomen. They have black heads, brownish dorsal thoracic plates, yellowish bodies with two rows of black spots along the back, and dark glands that can be turned outward, along each side of their abdomen. Chrysomela larvae are all quite similar, and adults are needed for species identification. Adult cottonwood leaf beetles are elongate-oval and are 0.5 to 1.0 cm long. They have a black head and the dorsal part of the first thoracic segment is black in the centre and reddish on the sides. The wing covers are yellowish with a dark line along the inner edges, and each one has seven elongate black spots. Adult beetles emerge in the spring and feed on the tender shoots by chewing many small holes through the leaves. Females lay their eggs in clusters on the leaves. The gregarious larvae feed by skeletonizing the leaves, consuming the entire leaf tissue except the midrib and most veins. Trees defoliated by leaf beetles often have thin and ragged foliage or a scorched appearance. Adults also feed gregariously on foliage before overwintering in the soil.

Damage: These leaf beetles generally prefer young foliage, and high populations may kill shoots and cause deformed growth. Young trees may be killed. Damage is most prevalent in hybrid poplar plantations. 

Similar Damage: Leaf beetles typically do not consume the midrib or the veins. Other skeletonizers (moth and sawfly larvae) generally consume most veins, leaving only the midrib and the largest veins.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated April 23, 2002