Leaf Beetles-Chrysomelidae



Leaf Beetles-Chrysomelidae

Commonly called leaf beetles, the Chrysomelidae are closely related to the Cerambycidae. Both families are plant eaters, and they share certain morphological similarities, especially in their leg structures. However, the two families are easy to separate. Except for the members of the subfamily Donaciinae (the long-horned leaf beetles), the Chrysomelidae do not display the lengthy antennae common to the Cerambycidae. Also, chrysomelids tend to be compact, oval, and small.

All the leaf beetles found in the United States are less than V2 inch in length. Most leaf beetles are handsomely colored. Many are serious pests; the adults and larvae can cause extensive damage to agricultural crops.

The Tortoise Beetles of the subfamily Cassidinae feed primarily on sweet potatoes, bindweeds, and morning glories. Chelymorpha cassidea, the largest member of this subfamily, is shaped much like a box turtle.

The larvae of the tortoise beetle are interesting in that they display a bizarre forked process at the end of the abdomen that resembles a second tail. This second tail, usually arched forward over the larva's body, collects excrement and skins cast off during molting; eventually, it resembles a dirty umbrella under which the beetle travels.

The Colorado Potato Beetle, Leptinotarsa decemlineata, is the best known North American pest in the family Chrysomelidae. Once confined to the Rocky Mountain area, this beetle originally fed on nightshades and wild potatoes. When potatoes began to be cultivated in the area in the early years of the iQth century, however, L. decemlineata moved down from the mountains and attacked the surrounding fields voraciously. Moving from potato crop to potato crop, the tiny beetle spread to most of the United States and was eventually exported to many parts of Europe.

The larvae of the Colorado potato beetle are brick red during the beginning of the larval stage. Later, they become yellow with black heads and markings. The larvae feed on potato leaves for about three weeks and then pupate underground. After 5 or 10 days, the new adult emerges and immediately flies to the nearest potato plant.

After mating, the females deposit their eggs on the undersides of potato leaves. A single female can produce more than 2,000 eggs, and there may be four generations in the span of a single year. The number of Colorado potato beetle generations depends upon the temperature, showing a marked increase in warmer regions.

Long-Horned Leaf Beetles. Leaf beetles of the subfamily Donaciinae have unusually long antennae and in this respect resemble the Cerambycidae. Dark, metallic, active beetles, they are usually found on water lilies, pond-weed, and other aquatic vegetation. The females usually lay their eggs on the undersides of water lilies. The larvae lead an underwater life, feeding on submerged vegetation and breathing through the stems of aquatic plants.

Cucumber Beetles. Acalymma vittata, the striped cucumber beetle, and its cousin Diabrotica undecempunctata, the spotted cucumber beetle, are both serious pests, feeding on the leaves, blossoms, and stems of a number of plants, including the cucumber. The spotted cucumber beetle is yellowish green and its elytra are marked with twelve black spots. The larvae of this species feed on corn and are commonly known as southern corn rootworms. The striped cucumber beetle is also yellowish-green but its elytra are decorated with three black stripes.

Both the striped and the spotted cucumber beetle are notable in that they are carriers of bacteria that cause a disease known as bacterial wilt. This disease causes plants to wilt and eventually die by plugging the water vessels of the stems and leaves. The cucumber beetles feed on diseased plants and then carry the wilt bacteria to healthy plants as they move in search of food. Even more significant in the spread of this disease is the fact that the bacteria live in the beetle's digestive tract during the winter, thus enabling them to survive the low temperatures.

Flea Beetles. Chrysomelids of the subfamily Alticinae, the tiny flea beetles have powerful hind legs that enable them to leap to safety when they are attacked. Many are serious pests-for example, Phyllotreta striolata, the striped flea beetle; Altica chalybea, the grape flea beetle; Chaetocnema confinis, the sweet potato flea beetle; Disonychia xanthomelas, the spinach flea beetle; and Epitrix cucumeris, the potato flea beetle.

Usually black, blue, green, or black with light markings, flea beetles injure plants by drilling tiny holes in the leaves. Plants wounded by flea beetles become especially vulnerable to bacterial wilt and blight.

Asparagus Beetles. Crioceris asparagi and C. duodecempunctata-the checkered and spotted asparagus beetles-are two other noted pests of this family. Both species feed on tender young asparagus shoots.

Asparagus beetles hibernate during the winter months, usually in old stalks of asparagus plants or in piles of garden debris. They emerge when the first asparagus shoots begin to appear and feed on the tender buds at the tips of the asparagus spears. The females, once they have satisfied their hunger, attach their bright black eggs to asparagus stalks. The small green or gray larvae feed on the plants on which they were born.

The major enemy of the asparagus beetles is Tetrastichus asparagi, the tiny "warrior wasp." All of the members of this species are females. These tiny spinster wasps feed on the eggs of the asparagus beetle, stabbing them with their ovipositors and then sucking out the tasty contents. T. asparagi, however, does not feed on all the eggs she finds-in some she lays her own eggs.

For a time, the egg of the asparagus beetle is not affected by this alien. An apparently normal asparagus beetle larva emerges from the egg and begins to feed on the asparagus plant as though the almost microscopic wasp egg were not present in its body. After a week or ten days, however, the asparagus beetle larva, in accordance with its nature, drops to the ground and begins to build a shell in which to pupate. This action on the part of the host prompts the wasp egg to hatch; the emerging larva begins to feed on the young beetle. Within a week, the asparagus beetle larva is dead.

Chrysomefa. Not all of the Chrysomelidae are pests. Some, like Chrysomela gemellata, are highly beneficial to man. C. gemellata, a purplish green, pea-sized beetle, was imported from Australia in 1949. It aids cattlemen by clearing range land of Klamath weed, a poisonous plant sometimes known as Saint John's wort. Acre after acre of Klamath weed has been replaced by healthy bunch grass.


INDEX : Insects   January 11, 2016 02:26:00 PM