This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
The following is by S. Arthur Johnson, in "Bulletin 175' of the Colorado Agricultural Experiment Station:
This insect (Leptinotarsa decemlineata) is a native of a strip of country which lies just east of the Rocky Mountain range and includes eastern Colorado. In its native state the beetle lives upon the wild weeds of the potato family. The chief of these is the buffalo bur, but the beetle is quite a general feeder on plants of this group, including not only potatoes, but tomatoes, eggplant, tobacco, and pepper.
The adult beetle is oval in shape, about three eighths of an inch in length and a trifle narrower than long. The ground color is yellow and the wings are marked by ten black lines running lengthwise. There are also black markings on the thorax. The eggs are bright yellow when fresh and are generally laid on the under surface of the leaves in patches containing from ten to fifty each. The young are dark red or brown grubs with black heads. The color becomes lighter as the grubs mature.
The adult beetles live over winter usually in the ground at a depth of from four to six inches. Where the ground is loose they frequently go much deeper. When the ground becomes warmed by the spring sun the beetles emerge and seek food plants on which they may feed and lay eggs. They are more or less abundant every year and do considerable damage to early potatoes. The late crops in Colorado generally escape because most of the adult beetles die off before the potatoes appear above ground.
The eggs hatch in from four to eight days, depending on the temperature. The larvae feed at first on the surface of the leaf where they hatch, but soon migrate to the top of the plant and eat the tender young leaves which are just unfolding. The young reach full growth about three weeks later. Soon eggs are laid again and the second generation hatches. Ordinarily, two broods are all that we may expect.
The best and most practical remedy is spraying with some arsenical poison. In commercial fields the best machine is a power sprayer drawn by horses. In garden patches a hand sprayer does very good work. Arsenate of lead, altogether the best poison, is a white paste which must be carefully mixed in a little water before it is poured into the spray machine. It should be strained through a fine screen in order to remove all lumps which might clog the nozzles. Apply the poison at the rate of six or eight pounds to a hundred gallons of water. The proper time to spray is when the grubs begin to appear at the tops of the stems. Arsenate of lead does not kill as quickly as Paris green, but it sticks to the leaves much longer and the benefits can be seen for weeks, even after rains. Paris green is the old standby, is cheaper for a single application, and is still the most used. This poison is mixed with water at the rate of a pound to seventy-five or one hundred gallons. There is danger that this substance will burn the foliage of the potato, and to avoid this it is well to add the milk from two pounds of slaked lime to each hundred gallons of water used. While spraying either of these poisons the contents of the spraying machine should be kept well agitated. Sometimes the pest is confined to small areas. In such cases the insects are often controlled by the use of dust sprayers, which either blow the Paris green out in fine clouds, or dust out the same poison when it has been mixed with flour or carefully screened air-slaked lime."