Univoltine larvae then enter diapause (developmental inactivity) when they reach the fifth instar, while the bivoltine larvae pupate inside the stalk during July and early August. The larvae complete their growth inside the stalk in about three weeks. Newly hatched larvae chew small, round holes in the leaves and then move to the main stalk. The time required for first-generation egg hatch is approximately seven to ten days after being laid, but hatch is temperature dependent so it could occur earlier or later depending on local weather. Females lay eggs from mid-May to mid-June. First generation adult emergence occurs from early May in southeastern areas to late June in northern counties and mating is facilitated by sex pheromones emitted by female moths. ![]() In spring, diapausing larvae emerge from dormancy and pupate from late April to early June with the univoltine population tending to emerge later than the bivoltine population. One strain is univoltine (one generation per year) and is generally found in the mid-state and northern regions, and the other strain is bivoltine (two or more generations per year) and is found throughout the state, though more so in southern portions. In Pennsylvania, there are two separate strains of ECB. The pupae are smooth, light to dark brown in color, and 1/3 to 5/8 of an inch in length. Pupae remain inside the host plant, and adults emerge in late spring and in July. The pupal stage of the corn borer is rarely visible. (Right) ECB larva tunneled into corn stalk. It is the larval (borer) stage that causes damage to crops. There are numerous dark spots scattered over the sides and top of the body. The larvae are dirty white, often having a pinkish tinge. After 3 to 5 days, the eggs change from white to a yellowish color, and then, just before hatching, a dark spot appears in each egg.Įuropean corn borer egg mass. Each egg is about half the size of a pin head. Clusters resemble fish scales overlapping one another. The eggs are usually glued to undersides of leaves, in small irregular-shaped clusters that are white and very flat, containing about a dozen or more individual eggs. ![]() (Right) European corn borer adult females. (Left) European corn borer adult male on corn leaf. Adults are most active during late evening. During the day, adults take shelter in grass, weeds, and crop residue in and around crop fields. They have several dark zigzag marks across the wings, and their wingspan is 3/4 to 1 inch. The adults are yellowish to light tan in color. Previous research in Pennsylvania suggested that corn borer was responsible for about a 5.5% yearly yield reduction in field corn however, because of widespread adoption of insect-resistant, transgenic corn hybrids (i.e., Bt hybrids) beginning in 1996, ECB populations appear to have declined in many parts of Pennsylvania, reflecting national declines. Instead, economic levels of ECB damage in Pennsylvania occur more commonly in sweet corn, peppers, and snap beans however, occasional moderate damage in corn occurs in some southern Pennsylvania fields. It is more commonly a pest of corn in Midwestern states, whereas losses in Pennsylvania field corn due to ECB are variable depending on historical infestation levels, weather conditions, and management. ECB has a very wide host range including, tomatoes, potatoes, snap beans, peppers, sorghum, corn, and many weed species. ![]() In Pennsylvania, ECB has been present as a pest for over 80 years. Since its introduction, it has established itself as a pest in most states east of the Rocky Mountains. It appears to have been introduced into the United States on broom corn imported from Hungary and Italy. The European corn borer (ECB), Ostrinia nubilalis (Hübner), was first identified near Boston, Massachusetts in 1917.
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