Many of our vegetable crops are subject to feeding by one or more species of flea beetles (Figure 1).
Figure 1. Flea beetles on brassica (photo by John Obermeyer)
Flea beetles get their name because they have enlarged hind legs that allow them to jump like fleas. Most species are quite small, and with their ability to jump, often seem to just disappear when disturbed. Flea beetles tend to feed on the leaves, chewing small round holes. When populations are high, the feeding holes with overlap, creating larger holes. Flea beetles tend to be early season pests, primarily because smaller plants are more affected by their feeding. Treatment thresholds vary from crop to crop. For example, eggplants, on of the most commonly damaged vegetable crops, should be treated when there is an average of 4 beetles per plant. For tomato, the threshold is when leaves are 30% defoliated. Crucifers have no particular threshold, so treatment should be made when leaves start to show considerable damage. Flea beetles are easy to control with a variety of insecticides including Sevin® and the pyrethroids. One application is usually all that is required.