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 facts about this insect (Epitrix cucumeris) which follow were written by S. Arthur Johnson for Colorado Agricultural Experiment Station, "Bulletin No. 175":
When tomatoes are first set out or potatoes first come up there may often be found on them tiny black beetles which jump when alarmed. They are called the flea beetles because of this habit, though they are not closely related to the flea.
The adult insects live over winter and appear during the latter part of May and first of June. They get their living by eating tiny holes in the surface of the leaves of plants of the potato family, and often attack cucumbers and beans. The insects often congregate in such numbers that the leaves of the plants appear almost black with them. Newly set tomato plants and young potatoes frequently have their leaves so badly eaten that they shrivel and the tomatoes may die. Ordinarily, the stand of the potato crop is not seriously injured in this way. Their greatest damage to potatoes in Colorado is done by the larvae, which live under ground. These larvae are tiny white grubs which attain a length of about a quarter of an inch. The first brood is to be found during June or early July. They frequently cut into and destroy the young tuber stems of the potatoes, thus preventing a regular setting of the crop. The second brood of larvae appear during August and September. This brood bores into the flesh and under the skin of the potatoes, causing a pimply or scabby development, which may cause great waste in preparing the tubers for the table and seriously depreciate their market value.
No satisfactory remedy for this pest is known. The leaf injuries to young potatoes and tomatoes may be largely avoided by spraying the leaves thoroughly with Bordeaux mixture to which Paris green is often added. The insects appear to avoid the parts of the plant covered with these disagreeable substances and to seek fresh tissues upon which to feed. It is not certain where the insects hibernate, but they are found often in the fall in large numbers feeding on stray potato plants or pieces of tubers which have been left in the fields. It is well to clear up the fields immediately after the crop is gathered. These insects are seldom, if ever, found on new ground, and are much worse where potatoes are planted in succession.'