Life cycle and description

• Adult stage: Female moths are pale yellow to light brown in color with a wingspan ranging from 25 to 35mm. Male moths are usually slightly darker and smaller with a wingspan of 20 to 25mm. Both males and females have forewings and hindwings characterized by dark zigzag lines with yellow patches. Adult moths are nocturnal and remain motionless in border vegetation during the day. Adult longevity ranges from 18 to 24 days. Females begin oviposition 4 days after emergence and continue oviposition for up to 14 days. On average, females lay 20 to 50 eggs a day. Females can mate multiple times resulting in increased fecundity. Minimum temperature required for flight is 13 to 15°C.
• Egg stage: Eggs are oval in shape (1mm in length and 0.75mm in width) and flattened. Eggs are initially creamy white in color but darken with age and the black head of the larva is visible just before hatching. Eggs are deposited in masses of 5 to 30 eggs on the underside of leaves where they overlap like roof tiles or fish scales. Eggs hatch in 4 to 9 days. Warm temperatures favor early hatching, although warm, dry winds can desiccate eggs.
• Larval stage: Larvae have 6 instars. Body length during the first instar is approximately 1.5mm, expanding to approximately 20mm in the final instar. Larvae are generally light brown, grayish or pinkish in color, with a dark brown or black head capsule and a light colored thoracic plate. The dorsal side of the body has a series of four anterior spots in each segment followed by two small posterior spots. Early instars feed in the whorl, predominantly on the tassel. Following tassel emergence, larvae burrow into the stem and ears. Total development time for larvae can take as long as 50 days although this is variable and depends on prevailing weather conditions. Larvae in the final instar stage can overwinter in tunnels in the maize stem.
• Pupal stage: Pupae are generally light brown in color and measures 13 to 17mm in length and 2 to 4mm in width. Female pupae are generally slightly larger than male pupa. The pupa is anchored to its cocoon by up to 8 spines emerging from the tip of the abdomen. Duration of the pupa stage ranges from 7 (26°C) to 12 (21°C) days depending on temperatures.
• There can be 1 to 4 generations per growing season depending on climatic regions and species strain. Warmer conditions favor more generations.
• Mature larvae overwinter in the diapause state in tunnels in maize stems, ears, and alternate hosts. Larvae make a small hole in the stem from which the adult can emerge.

Confirmation

Light and pheromone traps can be used to detect and confirm the identity of adult moths. Plants should be inspected for characteristic signs of damage, egg mass and presence of larvae. Larvae may need to be reared to adulthood for 100% confirmation via male genital examination.

Problems with similar symptoms

The European maize borer is often confused with the Asian maize borer (Ostrinia furnacalis) due to similar appearance and feeding damage. However, they can be distinguished by differences in geographic distribution. In North America, the European maize borer is likely to be confused with Smartweed borer (Ostrinia obumbratalis). Symptoms of damage (pinhole perforations in the whorl) are similar to that caused by the Southwestern corn borer (Diatraea grandiosella), Neotropical corn borer (D. lineolate) and the Sugarcane borer (D. saccharalis).

Why and where it occurs

Ovipositing females are attracted to weedy or grassy fields. Reduced tillage methods favor infestation as the larvae are able to overwinter in crop debris. Low precipitation, low wind, and warm temperatures favor moth survival and egg hatch.

Host range

European maize borers have an extremely wide host range and attack almost all herbaceous plants that have a stem large enough for the larvae to bore into. In addition to maize and other cereals, the European maize borer is a pest of legumes, pepper, potato, ornamental flowers, soybean, cotton, sunflower, tomato, and various wild grasses and weeds.

Geographic distribution

North America, Europe, north Africa

Damage

• Mechanism of damage: Boring in the stems and upper part of the maize plant will weaken the plant and can cause lodging or tassels to break off, in addition to impeding water and nutrient uptake. Boring in the ears can lead to ears breaking off, loss of kernels, commercial loss due to cosmetic damage to ears, and can make ears vulnerable to fungal infection and cob rots. Boring in the stems also interferes with translocation of water and nutrients, which is particularly serious if plants are under water stress.
• When damage is important: Boring of the stem can lead to serious crop lodging, while boring in the ear can lead to direct yield loss, cob rots and loss of commercial value. Boring of the ear can also make the ear vulnerable to fungal infection and ear rots that produce mycotoxins.
• Economic importance: Studies have indicated that yield loss as high as 6% are incurred per borer per plant. Yield losses as high as 30% have been recorded in Poland.

Management principles

Monitoring

• Sampling adult moth populations using light traps or pheromone traps can be used to assess incidence of European maize borers.
• Plants should also be inspected for characteristic egg masses on the underside of leaves and for first generation larvae feeding within the whorls.

Cultural control

• Management of stalks, which are the overwintering sites of larvae, can help reduce pest levels in the subsequent season. Mowing of stalks close to the soil level has been shown to eliminate up to 75% of larvae.

• In regions where a single generation of the pest occurs during the growing season, late planting can reduce damage. However, in seasons where multiple pest generations occur, later planted maize is often severely damaged.

Host resistance

• Host resistance is available in many maize hybrids. Hybrids have been developed with strong stalks that resist lodging after being bored by the European maize borer.
• Some resistant varieties release a chemical known as DIMBOA which serves as a repellent and feeding deterrent.

Biological control

• Parasitoid wasps such as Trichogramma species that attack the eggs have been used with some success in North America and Europe. However, this method usually requires extensive coordination and favorable weather conditions to be effective.
• Parasitoids native to Europe have been introduced to North America.
• Use of Bacillus thuringiensis (Bt) products can suppress pest infestations. For successful treatment Bt should be applied in the whorl when larvae are at the first instars. Bt is harmless to predators and parasitoids and integrated use of Bt and egg parasitoid release has been successful.

Chemical control

• Under sever infestation application of chemicals, particularly in granular form in the whorl, can provide effective means of pest management. Chemicals should be applied when larvae are still in the first or second instar in the whorl, just prior to tassel emergence. Chemicals can also be applied as a liquid spray to coincide with egg hatch.

References

Beres, P. and F. Lisowicz. 2005. Effectiveness of Trichogramma species in maize protection against European corn borer (Ostrinia nubilalis) in ecological farms. Progress in Plant Protection 45: 47-51.

Bohn, M., R.C. Kreps, D. Klein and A.E. Melchinger. 1999. Damage and grain yield losses caused by European corn borer (Lepidoptera: Pyralidae) in early maturing European maize hybrids. Journal of Economic Entomology 92: 723-31.

CAB International. 2002. Crop Protection Compendium. Wallingford, UK: CAB International.

Davidson, R.H. and W.F. Lyon. 1987. Insect Pests of Farm, Garden and Orchard. Hoboken, NJ: John Wiley & Sons.

Heinrichs, E.A., J.E. Foster and M.E. Rice. 2000. Maize Insect Pests in North America. Radcliffe’s IPM World Textbook. University of Minnesota. http://ipmworld.umn.edu/chapters/maize.htm#ECB (24 January 2007).

Capinera, John L. 2000. European corn borer. University of Florida Institute of Food and Agricultural Sciences. http://creatures.ifas.ufl.edu/field/e_corn_borer.htm (8 August 2007).

Contributors: Gabrielle Turner, David Bergvinson, and Biswanath Das