Of the dozens of species in the flea beetle family, most have specific taste in regards to the type of plant they feed upon; examples are beetles that feed solely on spinach, potato or corn plants. These insects can invade and devastate a crop within one night, if left unchecked. Affected plants can be harvested or destroyed.
Flea beetles are smal beetles ranging between 1/16 to 1/8 inch long, according to the University of Minnesota. Identification can be made by their color variations between black, blue, bronze, brown or metallic gray. They are called flea beetles because of their ability to jump like fleas; this is because of their large back legs, which are similar to fleas. The Penn State College of Agricultural Science notes that the larval stage of these beetles resembles a slender version of the corn rootworm. The larvae are milky white with a dark head and three pairs of legs immediately after the head. Evidence of flea beetle eggs can be identified by white, oblong tiny dots on plants.
Flea beetles can be found in crop field rows, roadsides and protected areas during winter; their preferred hibernation spots include the underside of fallen leaves and dirt clods. Common crops affected by various flea beetle species include corn, spinach, cabbage or any broadleaf vegetable plant.
The flea beetle hibernates during winter as an adult. In early spring, when vegetation first begins growth, the adult beetles exit hibernation and begin looking for food and places to deposit eggs. Beetle eggs are laid on leaves or in the cracks of the soil near root systems of the host plant, according to Penn State. The larval stage of this insect takes around 30 days to complete its cycle. The larvae dig into the soil and emerge later as adults. Flea beetles only have one or two generations during a single year.
Damage from flea beetles can be minor for small infestations with the greatest damage occurring to foliage, cotyledons and stems, according to the University of Minnesota, although larger infestations can destroy an entire garden. Every species of flea beetle leaves similar markings to damaged plants. The University of Minnesota identifies this damage as shallow pits or small, irregular rounded holes in leaves. Feeding paths run parallel to the veins, although these paths can cross the veins in a zigzag form. Heavier infestations can cause wilted and stunted plants. Biological pathogens can be introduced by the beetle causing seedlings to wilt and die. Lesions may appear on leaves indicating a pathogen introduced by the insect.
Flea beetle controls fall into four categories: cultural, physical, biological and insecticidal. Before attempting control, confirm flea beetles by placing sticky yellow traps.
Removing old crop debris, ground waste and leaves deprive adult beetles of hibernation spots near gardens. Planting the vegetable garden as late as possible allow plants to outgrow damage from beetles. Screens over gardens deprive the beetle of access while seedlings establish root systems. These screens must be removed before flowering to allow pollination. Trap crops, such as radish, that sprout greens early attract flea beetles away from the main crop which sprouts later in the season. This allows for easier extermination of the insect because this beetle finds the earliest and tallest crop to feed upon. Microctonus vittatae is a micro wasp that lays eggs in adult flea beetles. These wasps sterilize the female beetle as larvae and then kill the beetle as the wasp emerges from the beetle. Insecticides are applied as sprays stem the feeding of the adult beetle.