The European corn borer was first discovered in Massachusetts in 1917. Since then it has spread rapidly throughout North America westward to the Rockies. This insect is known to feed on over 200 different species of plants including corn, potatoes, beans, beets, celery, and peppers. Recently growers have complained about it's occurrence in the potato crop in some areas of the Maritimes.
Identification
The adult female of the European corn borer is about 19-25 mm in length with light brown wings and a dark irregular line across the wings. Males are generally smaller in size and darker in color. Both sexes have palps extending forward of the head which resembles a snout, characteristic of this family of moths.
Mature larvae are about 15-18 mm in length and are easily identified by their dark head capsule and paired dark spots running the length of the body along the back.
Life history
The European corn borer overwinters as fully grown larvae in the stem of its host plant. The larvae pupate in the spring and emerge as adults about the middle of July on Prince Edward Island. Flights of adults can be predicted when 300 degree-days have been accumulated. Degree-days are calculated by subtracting a base temperature of 10EC from the average daily temperature. Eggs are laid in masses containing 15 to 50 eggs per mass on the undersides of leaves of the potato plant. The black head capsules of developing alrvae become more visible within the eggs as they mature and are an indication that the larvae are about to hatch. Eggs hatch in about three to nine days in Maine and presumably in the same time span in Prince Edward Island. The newly emerged larvae feed on the leaves for a few days then bore into the stem of the plant. The larva completes its development in the stem and prepares to overwinter.
Crop injury
The larva damages the crop by entering the stem and destroying the pith, xylem, and phloem. Damaged plants are susceptible to wind damage, water stress, and invasion from pathogens such as blackleg. The impact of the European corn borer on the potato plant appears to be a function of larval numbers, phenological stage of the plant at the time of attach, the cultivar, presence of other insect pests and diseases, and other stress factors such as temperature, water, and fertility. Because the young larvae are present on the foliage for only a few days the window for control with a bacterial or synthetic insecticide is quite small. Insecticides are no longer effective after the larva has entered the stem.
Pest management
At present, no thresholds exist for control of the European corn borer on potatoes. However, data from Prince Edward Island indicated that 1.2 larvae/stalk/week reduced yields of Russet Burbank by a margin of 8-9%. Monitoring for this pest is best accomplished with water pan traps baited with the "Iowa" strain pheromone. The trap should be located in a grassy area adjacent to potato fields and checked frequently for adult males. When males are detected the field should be monitored for egg masses. Any applications of insecticides, if required, should be timed to control newly hatched larvae before they enter the plant's stem.