European corn borer
|European corn borer|
|Ostrinia nubilalis 
The European corn borer (Ostrinia nubilalis), also known as the European corn worm or European high-flyer, is a moth of the family Crambidae which includes other grass moths. This family of Lepidopterans has a distinct tympanic structure at the base of the abdomen called a praecinctorium, where two tympanic membranes are joined. This moth is a pest of grain, particularly maize. The insect is native to Europe, originally infesting varieties of millet, including broom corn. The European corn borer was first reported in North America in 1917 in Massachusetts, but was probably introduced from Europe several years earlier. Since its initial discovery in the Americas, the insect has spread into Canada and westward across the United States to the Rocky Mountains.
European corn borer caterpillars damage the ear, stalk, leaf sheath, and ear shank of corn by boring tunnels in the crops. In the United States, the economic impact from corn crop yield losses and population control expenses exceeds $1 billion annually. The damage the moth causes reduces the plants ability to photosynthesize, uptake nutrients and water, and fight infection.
- 1 Description
- 2 Geographic range
- 3 Life cycle
- 4 Mating
- 5 Parental care
- 6 Host plants
- 7 Pest of crop plants
- 8 Mutualism
- 9 Climate change
- 10 Gallery
- 11 See also
- 12 Notes
- 13 External links
The corn borer moth is about one inch long with a one-inch wingspan. The female moth is light yellowish-brown with dark, irregular, wavy bands across the wings. The male is slightly smaller and darker in coloration. The tip of its abdomen protrudes beyond its closed wings. The fully-grown larva is three-quarters to one inch in length. This borer is usually flesh-colored, but may range from light gray to faint pink, with conspicuous small, round, brown spots on each segment.
Female corn borer moths lay clusters of eggs on corn leaves, usually on the undersides. The egg masses, or clusters, are laid in an overlapping configuration and are whitish-yellow in color. As the larvae develop inside their eggs, the eggs become more and more transparent and the immature caterpillar black heads are eventually visible. The caterpillars hatch by chewing their way out of the eggs.
The European corn borer (Ostrinia nubilalis) is native to Europe and was introduced to North America in the early 20th century. This moth plagues corn crops in France, Spain, Italy, and Poland. In North America, the European corn borer is found in Eastern Canada and every state in the United States east of the Rocky Mountains.
The European corn borer progresses through four developmental stages. These are the egg, larva, pupa, and adult. The insect is referred to as a borer in its larval stage and as a moth in its adult stage. The adult moths lay their eggs on corn plants. Larva hatch from the eggs. Larvae have five instars or sub-stages of development. The larval stage is followed by a period of diapause or hibernation in a pupa. During the pupal stage, the borers progress through metamorphosis in a suspended chrysalis. Following this intense period of development, an adult moth emerges from the pupa. The length of the pupal stage is determined by environmental factors such as temperature, number of light hours, and larval nutrition in addition to genetics.
The bivoltine populations of European corn borers undergo the pupal stage twice during the spring months, first in May-June and then again in July-August. During the colder winter months, the European corn borer stays in its larval stage. Temperatures exceeding 50 degrees Fahrenheit induce the other developmental stages. The North American corn crop grows during these warmer months and provides a food source for the borers.
A female moth can lay two egg masses per night over 10 nights. The number of eggs per egg mass decreases each day with a majority of eggs laid before the seventh night. The female lays white eggs which then become pale yellow and finally translucent before hatching. The eggs hatch within three to seven days of oviposition.
Larva vary in color from light brown to pinkish grey and have distinctive dark spots along the body. As they grow they reach between 2mm and 20mm. The larva feed on the corn whorl and burrow into the stalk and ear. They have high mortality right after egg emergence but as soon as a feeding site is established, they have better survival rates. Total development before pupation is on average 50 days.
Diapause, also known as hibernation, in European corn borers is induced by temperature and changes in number of daylight hours. At higher temperatures, shorter photoperiods are sufficient to induce diapause. At 13.5 hours of light followed by 10.5 hours of dark, 100% of European corn borer larva entered diapause regardless of temperature with the range of 18 to 29 degrees Celsius. At high temperatures and long photoperiods, fewer larva enter diapause.
Adult corn borers are small, with the females having a greater wingspan of 35mm compared to the 25mm wingspan of males. They are generally a yellow to brown coloring. They are most active during the early dark hours of the day. The adults spend most of their time feeding and mating and have been found to have differing sex pheromones. 
The original European corn borers introduced to North America in the early 20th century established a population in New York. These populations were univoltine, meaning they produce one brood per year. A second population of European corn borers was introduced in Massachusetts and spread to Long Island and the Hudson River Valley. This second population is bivoltine meaning it produces two broods per year.
If presented with the opportunity, female European corn borers, like most moths, mate with multiple males in a reproductive strategy known as polyandry. Polyandry produces several benefits to female European corn borers. Multiple matings increase female fecundity and longevity, because female moths receive both nutritional resources and multiple spermatophores from males. Mating with multiple males ensures that the female receives enough sperm to completely fertilize her eggs. Additionally, it increases the reproductive fitness of females, because it increases the genetic diversity of the female’s offspring making it more likely that at least some of them will mate in the future and pass on her genes.
Female calling behavior in European corn borers involves the extrusion of the pheromone gland and release of sex pheromones. This calling behavior is influenced by the circadian rhythm of the moth and tends to occur at night. Higher humidity also induces the calling behavior, while desiccation, or drying out of the moths, decreases the calling behavior.
There are two strains of European corn borers that are defined by their sex pheromone communication variant. These strains are the Z and E strains named after the stereochemistry of the predominant isomer of 11-tetradecenyl acetate that these moths produce. The E variant of pheromone has a trans- configuration of hydrogen molecules around its double bond, while the Z variant has a cis- configuration. The Z strain produces a 97:3 ratio of Z to E isomer pheromone while the E strain produces a 4:96 ratio of Z to E isomer pheromone. A mixture of isomers is much more efficient at producing flight in a particular direction in both the Z and E strain as compared to a single component alone. 
The female European corn borer moth first lays eggs in June. The eggs are laid on the underside of corn plant leaves near the midvein. Oviposition forms a relatively normal distribution with 87.1% of egg masses laid on the leaf just below the primary ear leaf and an equal number of egg masses laid above and below this leaf with a slight bias towards the lower leaves. The egg masses are all laid within 5 leaves of the central ear leaf. Brood sizes range from 15-30 eggs and egg masses are about 6 mm in diameter.
The male European corn borer produces a spermatophore ejaculate that contains spermatozoa to fertilize the female and protein to nourish the female. The cost of producing a spermatophore is relatively low compared to the female investment in oviposition. Males mate an average of 3.8 times during their life time. On average, the refractory period between matings for the male European corn borer moth is 1.6 days. With each successive mating, the volume of the spermatophore decreases. This decreased spermatophore volume is associated with a decrease in female fecundity and fertility. Females who mate with males that have already mated before are less likely to deposit all of their eggs.
The European corn borer lives and feeds primarily on field corn, but also eats sweet corn, popcorn, and seed corn. The first generation of corn borers which develops during the late spring months feeds on the leaves and stalks of corn plants. The second generation feeds on these components of the plant in addition to the ear of corn, the leaf sheath, and the ear shank. If a third generation is produced, it will feed on the ear of corn, the leaf sheath, and the ear shank.
When corn is not abundantly present or is at the end of its harvest season, European corn borers will infest lima beans, peppers, potatoes, and snap peas. Rarely, these moths will live on various grains and soy plants or flowers.
Pest of crop plants
The European corn borer gets its name from boring holes into all components of the corn plant. The damage to the leaves reduces corn photosynthesis. Damage to the corn stalk decreases the amount of water and nutrients the plant can transport to the ear. European corn borers also eat the ear—which reduces crop yield—and the ear shank which often results in corn falling to the ground and making it unfit for harvest.
Bt corn, a variety of genetically modified maize, has had its genome modified to include a gene from the Bacillus thuringiensis ssp. kurstaki. As a result, the corn variety produces a protein that kills Lepidoptera larvae, in particular European corn borer.
Immature maize shoots accumulate a powerful antibiotic substance, DIMBOA, that serves as a natural defense against a wide range of pests and is also responsible for the relative resistance of immature maize to the European corn borer.
The presence of European corn borers on corn crops and the damage caused by them increases the likelihood of stalk rot caused by the pathogen Fusarium graminearum. The tunneling done by European corn borers makes it easier for F. graminearum to infect corn stalks and increases the amount of necrotic stalk tissue. The presence of F. graminearum in the tissue of corn infested by European corn borers speeds up the development of larva.
With the increase in temperature, it is predicted that the habitable region of the European corn borer will expand, further affecting agricultural crops. Additionally, an increase in the number of generations is expected. The CLIMEX model, which uses climatic responses of an organism and meteorological data, predicts that the area of arable land that will be affected by the European corn borer in Europe will increase by 61%.
- "Ostrinia nubilalis". Integrated Taxonomic Information System. Retrieved July 6, 2007.
- S., ARORA, R., SINGH, BALWINDER, GOSAL, S. BIOLOGICAL AND MOLECULAR APPROACHES IN PEST MANAGEMENT. [Place of publication not identified]: SCIENTIFIC PUBLISHER (IND. ISBN 9386102277. OCLC 958782397.
- Caffrey, D. J.; Worthley, L. H. Details - A progress report on the investigations of the European corn borer / - Biodiversity Heritage Library. doi:10.5962/bhl.title.108390.
- "The European Corn Borer | The European Corn Borer". www.ent.iastate.edu. Retrieved 2017-10-25.
- Vinal, Stuart Cunningham (1917). The European Corn Borer, Pyrausta Nubilalis Hu Bner: A Recently Established Pest in Massachusetts. Chicago: Massachusetts Agricultural Experiment Station. pp. 147–149.
- Martel, C.; Réjasse, A.; Rousset, F.; Bethenod, M.-T.; Bourguet, D. (2003). "Host-plant-associated genetic differentiation in Northern French populations of the European corn borer". Heredity. 90 (2): 141–149. doi:10.1038/sj.hdy.6800186. ISSN 0018-067X.
- "The European Corn Borer | The European Corn Borer". www.ent.iastate.edu. Retrieved 2017-10-25.
- "Life Cycle and Generational Ecotypes of the European Corn Borer | The European Corn Borer". www.ent.iastate.edu. Retrieved 2017-10-25.
- Phelan, P. L.; Norris, K. H.; Mason, J. F. (1996-12-01). "Soil-Management History and Host Preference by Ostrinia nubilalis: Evidence for Plant Mineral Balance Mediating Insect–Plant Interactions". Environmental Entomology. 25 (6): 1329–1336. doi:10.1093/ee/25.6.1329. ISSN 0046-225X.
- Beck, S.D.; Hanec, W. "Diapause in the European corn borer, Pyrausta nubilalis (Hübn.)". Journal of Insect Physiology. 4 (4): 304–318. doi:10.1016/0022-1910(60)90056-1.
- "European corn borer - Ostrinia nubilalis (Hubner)". entnemdept.ufl.edu. Retrieved 2017-10-30.
- Glover, T. J.; Tang, X.-H.; Roelofs, W. L. (1987-01-01). "Sex pheromone blend discrimination by male moths fromE andZ strains of European corn borer". Journal of Chemical Ecology. 13 (1): 143–151. doi:10.1007/BF01020358. ISSN 0098-0331.
- Fadamiro, Henry Y; Baker, Thomas C. "Reproductive performance and longevity of female European corn borer, Ostrinia nubilalis: effects of multiple mating, delay in mating, and adult feeding". Journal of Insect Physiology. 45 (4): 385–392. doi:10.1016/s0022-1910(98)00137-1.
- Royer, L.; McNeil, J. N. (1991-11-01). "Changes in calling behaviour and mating success in the European corn borer (Ostrinia nubilalis), caused by relative humidity". Entomologia Experimentalis et Applicata. 61 (2): 131–138. doi:10.1111/j.1570-7458.1991.tb02405.x. ISSN 1570-7458.
- Klun, J. A. (1975-12-01). "Insect Sex Pheromones: Intraspecific Pheromonal Variability of Ostrinia nubilalis1 in North America and Europe2". Environmental Entomology. 4 (6): 891–894. doi:10.1093/ee/4.6.891. ISSN 0046-225X.
- Orr, David B.; Landis, Douglas A. (1997-08-01). "Oviposition of European Corn Borer (Lepidoptera: Pyralidae) and Impact of Natural Enemy Populations in Transgenic Versus Isogenic Corn". Journal of Economic Entomology. 90 (4): 905–909. doi:10.1093/jee/90.4.905. ISSN 0022-0493.
- "Plant and Soil Sciences eLibrary". passel.unl.edu. Retrieved 2017-10-25.
- Royer, L.; McNeil, J. N. (1993). "Male Investment in the European Corn Borer, Ostrinia nubilalis (Lepidoptera: Pyralidae): Impact on Female Longevity and Reproductive Performance". Functional Ecology. 7 (2): 209–215. doi:10.2307/2389889.
- University of Kentucky Extension Service Bt Corn - What it is and how it works
- Chiang, H. C.; Wilcoxson, R. D. (1961-10-01). "Interactions of the European Corn Borer and Stalk Rot in Corn". Journal of Economic Entomology. 54 (5): 850–852. doi:10.1093/jee/54.5.850. ISSN 0022-0493.
- Kocmánková, E.; Trnka, M.; Eitzinger, J.; Dubrovský, M.; Štěpánek, P.; Semerádová, D.; Balek, J.; Skalák, P.; Farda, A. (2011). "Estimating the impact of climate change on the occurrence of selected pests at a high spatial resolution: a novel approach". The Journal of Agricultural Science. 149 (2): 185–195. doi:10.1017/s0021859610001140. ISSN 1469-5146.