European corn borer

The European corn borer (Ostrinia nubilalis), also known as the European corn worm or European high-flyer, is a moth of the family Crambidae. It is a pest of grain, particularly maize (Zea mays). 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.^[2] Since its initial discovery in the Americas, the insect has spread into Canada and westwards across the United States to the Rocky Mountains.

The adult European corn borer is about 25 millimetres (0.98 in) long with a 26–30 millimetres (1.0–1.2 in)^[3] wingspan. The female is light yellowish brown with dark, irregular, wavy bands across the wings. The male is slightly smaller and darker.

European corn borer caterpillars damage corn by chewing tunnels through many parts of the plant, leading to a decrease in agricultural yield.

Geographic range[edit]

The European corn borer is native to Europe and was introduced to North America in the early 20th century.^[4] 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 U.S. state east of the Rocky Mountains.^[5]

Mating[edit]

Breeding cycle[edit]

The original European corn borers introduced to North America in the early 20th century established a population in New York. This population produced one brood per year. A second population was introduced in Massachusetts and spread to Long Island and the Hudson River Valley. This second population produces two broods per year.^[11]

Polyandry[edit]

If presented with the opportunity, female European corn borers, like most moths, mate with multiple males in a reproductive strategy known as polyandry. Polyandry confers several benefits to the females. For example, multiple matings increase female fecundity and longevity, because female moths receive both nutritional resources and multiple spermatophores from males. Furthermore, 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 – thus increasing the likelihood that they will mate and pass on her genes.^[12]

Sex pheromones[edit]

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 moth's circadian rhythm and tends to occur at night. Higher humidity also induces the calling behavior, while desiccation, or drying out, decreases the calling behavior.^[13] Both male and female European corn borers produce sex pheromones.^[14]

There are two strains of European corn borers that are defined by their sex pheromone communication variant. These are the Z and E strains, named after the stereochemistry of the predominant isomer of 11-tetradecenyl acetate that they produce.^[11] 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 in attracting the moth than a single component.^[15]^[11] The Z and E strains can mate and produce intermediate variants.^[16]

Host plants[edit]

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 feeds on the leaves and stalks of corn plants. In addition, the second generation feeds on the ear of corn, the leaf sheath, and the ear shank. If a third generation is produced, it will feed on the ear, the leaf sheath, and the ear shank.^[4]^[19]

When corn is not abundant or near the end of the harvest season, European corn borers will infest lima beans, peppers, potatoes, and snap peas. Rarely, these moths will live on other grains, soybeans, or flowers.^[19]

Mutualism[edit]

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 corn infested by European corn borers also speeds the development of larvae.^[25]

Climate change[edit]

With the increase in temperature associated with climate change, it is predicted that the habitable region of the European corn borer will expand. Additionally, an increase in the number of generations is expected. The CLIMEX model, which models organisms' response to climate change, predicts that the area of arable land affected by the European corn borer in Europe will increase by 61%.^[26]