European Corn Borer
Ostrinia nubilalis (HÅbner)


Life Cycle and Description: The number of generations varies from one to four, with only one generation occurring in northern New England and Minnesota and in northern areas of Canada, whereas three to four generations occur in Virginia and other southern locations. In many areas generation number varies depending on weather, and there is considerable adaptation for local climate conditions even within strains. European corn borer overwinters in the larval stage, with pupation and emergence of adults in early spring. Diapause apparently is induced by exposure of last instar larvae to long days, but there also is a genetic component. Moth flights and oviposition usually occur during June-July and August-September in areas with one to two generations annually. In southern locations with three generations, moth flights and oviposition typically occur in May, late June, and August. In locations with four generations, adults are active in April, June, July, and August-September.

Egg: Eggs are deposited in irregular clusters of about 15 to 20. The eggs are oval, flattened, and creamy white in color, usually with an iridescent appearance. The eggs darken to a beige or orangish tan color with age. Eggs normally are deposited on the underside of leaves, and overlap like shingles on a roof or fish scales. Eggs measure about 1.0 mm in length and 0.75 m in width. The developmental threshold for eggs is about 15°C. Eggs hatch in four to nine days.

Larva: Larvae tend to be light brown or pinkish gray in color dorsally, with a brown to black head capsule and a yellowish brown thoracic plate. The body is marked with round dark spots on each body segment. The developmental threshold for larvae is about 11°C. Larvae normally display six instars. Head capsule widths are about 0.30, 0.46, 0.68, 1.03, 1.66, and 2.19 mm in instars 1 through 6, respectively. Mean body lengths during the six instars are about 1.6, 2.6, 4.7, 12.5, 14.5, and 19.9 mm, respectively. Young larvae tend to feed initially within the whorl, especially on the tassel. When the tassel emerges from the whorl, larvae disperse downward where they burrow into the stalk and the ear. Mortality tends to be high during the first few days of life, but once larvae establish a feeding site within the plant survival rates improve. Larvae in the final instar overwinter within a tunnel in the stalk of corn, or in the stem of another suitable host. Duration of the instars varies with temperature. Under field conditions development time was estimated at 9.0, 7.8, 6.0, 8.8, 8.5, and 12.3 days for instars 1 through 6, respectively, for a mean total development period of about 50 days, but this varies considerable from year to year according to weather conditions.

Pupa: Pupae usually occur in April or May, and then later in the year if more than one generation occurs. The pupa is normally yellowish brown in color. The pupa measures 13 to 14 mm in length and 2 to 2.5 mm in width in males and 16 to 17 mm in length and 3.5 to 4 mm in width in females. The tip of the abdomen bears five to eight recurved spines that are used to anchor the pupa to its cocoon. The pupa is ordinarily, but not always, enveloped in a thin cocoon formed within the larval tunnel. Duration of the pupal stage under field conditions is usually about 12 days. The developmental threshold for pupae is about 13°C.

Adult: The moths are fairly small, with males measuring 20 to 26 mm in wingspan, and females 25 to 34 mm. Female moths are pale yellow to light brown in color, with both the forewing and hind wing crossed by dark zigzag lines and bearing pale, often yellowish, patches. The male is darker in color, usually pale brown or grayish brown, but also with dark zigzag lines and yellowish patches. Moths are most active during the first three to five hours of darkness. The sex pheromone has been identified as 11-tetradecenyl acetate, but eastern and western strains differ in production of Z and E isomers. The preoviposition period averages about 3.5 days. Duration of oviposition is about 14 days, with oviposition averaging 20 to 50 eggs per day. The female often deposits 400 to 600 eggs during her life span. Total adult longevity is normally 18 to 24 days.