Western Poplar Clearwing
Solomon, J.D. 1995. Guide to Insect Borers in North American Broadleaf Trees and Shrubs. Agriculture Handbook 706. Washington, DC. United States Department of Agriculture, Forest Service. 735 p.
Poplar, willow, birch. Poplars are generally favored. Black cottonwood, balsam poplar, and white poplar, as well as several hybrids poplars, are recorded hosts (Beutenmuller 1901, Engelhardt 1946). Many other species of poplars are probably susceptible. Willows seem preferred in some areas of California and Oregon (Thompson 1927). Birch is occasionally attacked, and black locust has been listed as a host but needs to be confirmed (Beutenmuller 1901, Duckworth and Eichlin 1978).
From sea level to near timber line (Duckworth and Eichlin 1978), Alaska southward along the Pacific Coast to southern California and throughout the Rocky Mountains into the desert Southwest and as far east as Kansas and North Dakota (Engelhardt 1946).
Yellow-black clearwing moth. Male wingspan 23 to 30 mm and female wingspan 30 to 36 mm (Engelhardt 1946). Forewings orange brown with somewhat darker veins (Beutenmuller 1901). Hindwings transparent with conspicuous deep yellow discal mark; fringed with dark brown scales (Engelhardt 1946). Orange-brown antennae (Beutenmuller 1901), bipectinate in male and simple in female (Engelhardt 1946). Black head with yellow face and collar of depressed black and yellow scales (Engelhardt 1946). First three abdominal segments black; segments 2 and 3 with narrow yellow bands on posterior edges; remaining segments essentially yellow (Beutenmuller 1901). Coxae and femora of legs black and tibiae and tarsi yellow (Engelhardt 1946).
Oval and brown with reticulated surface, 1.0 to 1.2 mm across greatest axis.
White to grayish white with brown head and thoracic shield. Larva with pair of jointed legs on each thoracic segment and reachs 23 to 30 mm long. A setal map of body chaetotaxy can distinguish P. robiniae larva from closely related P. dollii (Eroles-Harkins 1983).
Brown, shiny, and 18 to 20 mm long.
Adults emerge mostly March to August, depending on location (Doane and others 1936). In central California, most emerge by mid-June; in eastern Washington, as late as mid-September (Thompson 1927). In the species' extreme southern range in California, specimens have been taken from February through May and again in November (Duckworth and Eichlin 1978). Females oviposit singly in bark crevices, around knots and wounds, and on other rough places of the bark of trunks and large limbs (Thompson 1927). Eggs hatch after about 20 days. Newly hatched larvae crawl over the bark for a few hours before selecting suitable sites to begin feeding. The larvae initially excavate cavities in the phloem and cambium and later galleries into the wood. Galleries are 5 to 10 cm long. Larvae feed during two successive summer and fall seasons; the first winter in galleries loosely packed with frass and the second winter in pupal chambers near the distal ends of the galleries. Distal ends are capped with silk, but no cocoons are formed. Pupation lasts 2 to 3 weeks (Duckworth and Eichlin 1978) to 30 days (Thompson 1927), depending on range. A generation requires 2 years over most of its range but may be of shorter duration in its southern range (Duckworth and Eichlin 1978).
Injury and Damage
Trunks and larger branches (particularly of young trees) are most apt to be attacked (Duckworth and Eichlin 1978). Sap oozing from the bark and light brown granular frass ejected from bark are good evidence of infestation. Heavily infested trunks may become swollen and appear galled and cankered and have numerous entrance and exit holes. Dissection of infested stems reveals irregularly shaped cavities in the cambium and galleries extending into wood. Trees weakened or stressed by planting or transplanting, disease, wounds, and poor sites are most susceptible. Repeatedly attacked trees have open entrances and bark scars in all degrees of healing. Branches broken at tunneled sites and cast pupal cases protruding from exit sites are good evidence of infestation. The western poplar clearwing is a serious pest of ornamental trees in residential areas and parks in the West, where it kills and seriously deforms many trees. More recently this borer has damaged nurseries and young plantations.
Little is known about natural and cultural controls. One hymenopterous parasite--Apanteles paranthrenidis Mueseback--has been recorded (Marsh 1979); woodpeckers take large numbers of the larvae in some areas. The nematode Steinernema feltiae Filipjev has been used experimentally and has given 88 to 90% control of natural infestations (Kaya and Lindegren 1983). Because the borer prefers weakened trees, infestations could undoubtedly be reduced and injury minimized by cultural practices that promote tree health and vigor. Preliminary trials with chemical sprays have provided some control.