European Corn Borer
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Hosts
Sycamore, polar, yellow-poplar, peach, apple, pear. This polyphagous species feeds on plants representing 131 genera of 40 families including grains, grasses, weeds, herbaceous plants, flowers, and trees (Hodgson 1928). Corn is the preferred nonwoody plant. Trees are attacked only occasionally unless growing near heavily infested preferred hosts (Anonymous 1979, Tedders and others 1981).
Range
Introduced into the United States during the early 1900's and spread throughout the corn-growing areas east of the Rocky Mountains (Baerg 1951).
Description
Adult
Brownish moth with 24- to 29-mm wingspan (Vinal and Caffrey 1919). Forewings yellowish and brown with some streaking, banding, and spotting; hindwings grayish brown (Vinal and Caffrey 1919). Head covered with light yellowish brown scales. Dorsum of thorax cinnamon brown in males and light yellowish brown in females.
Egg
Circular to oval and slightly convex on upper surface, averaging 0.97 mm long and 0.74 mm wide. Egg surface sculptured with shallow pentagonal pits. When first deposited, eggs opaque to iridescent white and within 2 days assume yellowish tinge (Vinal and Caffrey 1919).
Larva
Measures about 25 mm long with head capsule width of about 2.2 mm when mature. Head and thoracic shields shiny brown and mottled with black. Dirty white to pink body, gray or light brown with narrow, dark brown median line on dorsum; broad, pale brown to pink subdorsal line; and narrow, pale brown lateral line. Freshly abdominal prolegs bear almost complete circle of crochets (Peterson 1962, Vinal and Caffrey 1919).
Pupa
Light to dark brown and about 14 to 17 mm long. Tenth abdominal segment extended to form dark brown to black cremaster bearing eight long, hooked spines.
Biology
This borer overwinters within tunnels in its host as mature larvae, which pupate in May and emerge as adults during June in Illinois. Females deposit 500 to 600 eggs on leaves of host plants; egg incubation is about 1 week. In herbaceous hosts, young larvae feed on tassels and leaf sheaths and later burrow in stems and fruits. Development of first generation is completed in July; most moths emerge during August. Larvae of the second generation feed on, or within, hosts until the advent of severe winter weather. Larval feeding is resumed during spring. This borer has one or two generations per year (Baerg 1951, Vinal and Caffrey 1919).
Injury and Damage
On tree seedlings, the first sign of infestation is rapid wilting and dying of foliage, terminal leaders, and lateral branch tips, which at first may appear to be caused by a leaf disease. Closer inspection reveals large holes, up to 6.5 mm in diameter, in stems just above the lateral leaf axils, or occasionally just below the leaf axils. Noticeable quantities of large granular frass and excrement accumulate near entrances. The larval tunnel, kept relatively free of frass, extends in the pith from the entrance hole almost to the terminal bud and may extend several centimeters below the entrance hole.* On peach seedlings, injury can range from 2-mm-diameter holes in the bark to injuries that cause 10-mm-diameter limbs to break under their own weight. A conspicuous gummy exudate mixed with frass accumulates at larval feeding sites (Tedders and others 1981). In northern Italy, it causes considerable injury in tree nurseries by boring into succulent stems and lateral shoots of poplar seedlings, particularly clones that have strongly developed medullary tissue like that in eastern cottonwood (Anonymous 1979). About 90% of the limbs on 1- and 2-year-old trees in a Georgia peach orchard were damaged by larvae that had migrated late in the season from browntop millet that had been interplanted among the trees (Tedder and others 1981). In a similar case, 30% of the terminal shoots of 1-year-old sycamore nursery stock, and some yellow-poplar seedlings, were tunneled by larvae in an Indiana nursery.* In every recorded instance of significant damage to tree seedlings, more preferred hosts such as corn, cover crops, or weeds, either grew nearby or were interplanted with the trees. In such cases, the trees were attacked in late summer by larvae that had migrated from the herbaceous plants.
Control
Numerous parasites have been recorded (Arnaud 1978, Krombein and others 1979). Several insect parasites have been introduced from Europe to control the borer, and appreciable results have been obtained in some areas. Populations are adversely affected by dry summers and cold winters. Crows and other birds are effective larval predators (Baerg 1951). Despite many natural enemies of this borer, populations have to be controlled by insecticides, cultural methods, and planting resistant plant varieties. Cultural controls include plowing under infested herbaceous host plants and shredding or storing hosts in silos to destroy hibernating larvae. Several insecticides are registered for control and are effective when properly timed and applied.
- Marshall, P.T. August 31, 1978. (personal communication). Indiana Department of Natural Resources, Vallonia, IN.
Gallery
 Photo by James Solomon, USDA Forest Service, Bugwood.org |  Photo by Ronald Smith, Auburn University, Bugwood.org |
References
Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC: U.S. Department of Agriculture, Forest Service. 735 p.
