There are many insects which are extremely destructive to potatoes; wire-worms, potato tuber moth, eastern potato leafhopper, eastern potato flea beetle, tuber flea beetle and the true potato aphids, white grubs and seed corn maggot are occasionally troublesome in some districts.
Wireworms.Wireworms are the most destructive insect pests of potatoes. These hard, shiny, yellow worms bore into the potato tubers and into seed pieces. The adults are slender, brown or black, hard-shelled beetles known as click beetles. They are present in the adult stage for but a short time in the spring during the mating egg-laying period.
Almost their entire life of several years is spent beneath the surface of the soil.
Intel-mountain Potato Leafhoppers. Adult intermountain potato leafhoppers are slender, wedge-shaped, pale green insects about 3 cm long. In the adult stage they apparently pass the winter in grass and weeds, at the margins of fields and elsewhere. They emerge in the spring and begin laying eggs in the tissues of their favourite host plants. The eggs hatch in about a week to 10 days, and the nymphs, which are smaller than the adults and wingless, feed upon the leaves of the host plant. Their feeding causes a speckled, white-stippled appearance of the leaves, especially the lower ones. These insects do not cause severe damage to potatoes and are not responsible for early maturity of potato vines.
Aphids. The true potato aphid is very destructive to potatoes in some regions.
Other aphids occur on potatoes but rarely cause damage. Leaves which are heavily infested curl, turn yellow or brown and die. Aphids are small, green or greenish-yellow, softbodied insects which feed in clusters, chiefly on the undersides of leaves. The winged forms migrate to potatoes from other plants or adjacent fields.
Colorado Potato Beetles. Adults of the Colorado potato beetles are plump, yellow and black striped insects. There are five black lines running length-wise on each wing. The eggs are orange-yellow and are deposited in clusters of 10 to 12 on the undersides of potato leaves. The young are brick-red hump backed larvae about 10 — 12 mm long. The colour changes to orange as the larvae grow. There are two rows of black spots along each side of the body.
Both the adults and their young feed upon the foliage of potatoes and closely related plants, often completely defoliating the vines. Mature larvae drop to the ground and burrow into the soil a short distance to pupate. They remain in this stage 5 to 10 days and then change to the adults. They pass the winter as adults at a depth of 15 to 20 cm in the soil. A partial second generation is sometimes produced. Fields should be watched closely during the spring and early summer for the presence of the beetles on the young plants. If only a few beetles are found they may be destroyed by hand with little effort and thus many later infestations prevented. Such procedure might easily delay for some time the need for expensive spraying or dusting machinery.
Dusting potato plants with calcium arsenate is effective in controlling the potato beetle. Calcium arsenate dust applied with a hand duster is especially recommended for use in home gardens and in large fields where the insects are found in only a few scattered places. Calcium arsenate dust is diluted at the rate of 1 part to 3 parts of inert carrier such as talc, diatomaceous earth, hydrated lime or low-grade flour.