NC State Extension Publications

Key to Pests of Beans and Peas

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The pests of beans, southern peas, and English peas are a diverse group. Mites and beetles are usually the most common pests of beans. Aphids frequently infest English peas, and stink bugs and leaffooted bugs (Figure D) are nuisances of southern peas. Some aphids transmit virus diseases.

A. Pests that feed primarily on the foliage

  1. Insects that mine or eat holes in the foliage
    1. Bean leaf beetle – These reddish to yellowish-brown beetles are 5 to 6 mm long and often have three black spots on each wing cover (Figure 1). They have black margins and a black triangle on the front portion of the wings. Bean leaf beetles consume mostly young leaves although the outer wall of pods are sometimes attacked when vegetative growth ends.
    2. Mexican bean beetle – Copper red, dome-shaped Mexican bean beetles are 6 to 8.5 mm long; each wing cover has eight small black spots that form three rows across the body when wings are at rest (Figure 2). These beetles skeletonize leaves which become lace-like and eventually turn brown from their feeding.
    3. Vegetable leafminer – Colorless to bright yellow, vegetable leafminers are maggots which grow up to 3 mm long (Figure 3). The head is pointed. These maggots make serpentine mines, slightly enlarged at the new end.
  2. Sap-sucking pests that cause discoloration, deformation, or abscission
    1. Aphids – Aphids are soft-bodied, pear-shaped insects with a pair of dark cornicles (tailpipe-like appendages) and a cauda (tail) protruding from the abdomen; they may be winged or wingless - wingless forms most common (Figure 4A-D). Aphids feed in colonies and cause discoloration, curling, and deformation of foliage. They often transmit virus diseases, and they excrete honeydew on which sooty mold grows.
      1. Bean aphid – Dark green to black, bean aphids have white appendages. They grow to 2.6 mm, and the cornicles are about the same length as the cauda (Figure 4A). Nymphs are green; mature nymphs have five to seven pairs of white spots on abdomen.
      2. Cowpea aphid – Cowpea aphids are black with white appendages and up to 2.5 mm long (Figure 4B). The cornicles are barely longer than the cauda. Nymphs are pale green to gray with a powdery coating.
      3. Melon aphid – Yellow to green, melon aphids have dark cornicles and cauda (Figure 4C). They feed in colonies and wingless forms are most common.
      4. Potato aphid – Pink, mottled or light green, potato aphids have a dark stripe (Figure 4D). Adults are up to 3.5 mm long, and the cornicles are slender and about twice as long as the cauda.
        1. Potato leafhopper – Spindle-shaped and up to 3 mm long, potato leafhoppers are green with yellowish to dark green spots (Figure 5). They usually jump instead of fly when disturbed. Potato leafhoppers extract sap from the undersides of leaves causing them to crinkle and curl downward (Figure E). Infested plants become yellow or bronzed and dwarfed.
        2. Thrips – Spindle-shaped and 1.2 mm or less in length, thrips are yellow, amber, brown, or black. Adults have two pairs of wings which are fringed and have brown crossbands (Figure 6). Immature thrips are white or yellow with red eyes. Thrips are pests during hot, dry weather. They cause whitish flecks or streaks on leaves and blossoms, and they deposit black specks of excrement.
        3. Twospotted spider mite – Tiny (almost microscopic) pale to dark green, twospotted spider mites have two or four darkly colored spots. Adults and nymphs have eight legs (Figure 7). Larvae have six legs. Females are oval and 0.3 to 0.5 mm long. Males are somewhat diamond shaped. Infested foliage becomes silvery because of pale yellow stipples. Leaves eventually become pale and die. Silken webs are spun on the underside of leaves as the mites feed.

B. Insects that feed on pods

  1. Corn earworm – Early instars of corn earworms are cream colored or yellowish green with few markings. Later instars are green, reddish or brown with pale longitudinal stripes and scattered black spots (Figure 8). Corn earworms are moderately hairy and grow to 44 mm long. They have three pairs of legs and five pairs of prolegs. They attack beans in fall and eat holes in pods.
  2. European corn borer – These caterpillars are grayish pink with a dark head and rows of small brown doughnut-shaped spots on the back (Figure 9). European corn borers grow to about 26 mm long and bore into the pods.
  3. Cowpea curculio adult and larva (Figure 10A-B) – Adults are black humpbacked weevils 6 to 7 mm long. Larvae are pale yellow and have brown heads. Larvae are legless and grow 6 to 7 mm long. Curculios leave feeding scars - small holes in pods and peas; larvae feed inside green seeds.
  4. Stink bugs – Adults are green or brown shield-shaped insects up to 19 mm long; nymphs are pale green or green with orange and black markings (Figure 11A-B, Figure I). Stink bugs pierce buds, pods, and seeds and cause buds to be malformed and plants weakened.

C. Insects which damage seeds and roots and bore in stems

  1. Bean leaf beetle larva – The whitish larva (up to 10 mm long) are dark at both ends and have three pairs of prolegs near the head (Figure 12). They are minor pests of bean roots.
  2. Lesser cornstalk borer – These slender, bluish-green caterpillars are up to 19 mm long and have brown rings around the body, three pairs of legs near the head, and five pairs of prolegs on the abdomen (Figure 13). Young larva bore into stems and sometimes disrupt the growing point.
  3. Limabean vine borer – Gray when young, these caterpillars later become bluish-green and sparsely covered with long yellowish hairs. Limabean vine borer caterpillars grow up to 25 mm long and have three pairs of legs near the head and five pairs of prolegs on the abdomen (Figure 14). They move from the leaves into stems, usually near nodes where they cause galls up to 70 mm long and 20 mm around to develop. Short, loose, silky frass tubes are connected to entrance holes.
  4. Seedcorn maggot – White to yellow-white maggots up to 7 mm long (Figure 15) feed on seed contents causing poor germination and tall spindly seedlings. Seedcorn maggots have no legs. The head is pointed.
Figure 1. Bean leaf beetles are reddish to yellowish-brown and

Figure 1. Bean leaf beetles are reddish to yellowish-brown and often have three spots on each wing cover.

Figure 2. Mexican bean beetles are copper red and dome-shaped

Figure 2. Mexican bean beetles are copper red and dome-shaped with black spots.

Figure 3. Vegetable leafminer maggots are colorless to bright y

Figure 3. Vegetable leafminer maggots are colorless to bright yellow with pointed heads.

Figure 4A-D. Aphids are soft-bodied, pear-shaped insects

Figure 4A-D. Aphids are soft-bodied, pear-shaped insects with a pair of dark cornicles (tailpipe-like appendages) and a cauda (tail) protruding from the abdomen; they may be winged or wingless.

Figure 4A. Bean aphids are dark green to black, with white appen

Figure 4A. Bean aphids are dark green to black, with white appendages.

Figure 4B. Cowpea aphids are black with white appendages and up

Figure 4B. Cowpea aphids are black with white appendages and up to 2.5 mm long.

Figure 4C. Melon aphids are yellow to green and have dark cornic

Figure 4C. Melon aphids are yellow to green and have dark cornicles and cauda.

Figure 4D. Potato aphids are pink, mottled or light green and ha

Figure 4D. Potato aphids are pink, mottled or light green and have a dark stripe.

Figure 5. Potato leafhoppers are spindle-shaped, up to 3 mm long

Figure 5. Potato leafhoppers are spindle-shaped, up to 3 mm long and are green with yellowish to dark green spots.

Figure 6. Thrips are spindle-shaped, 1.2 mm or less in length an

Figure 6. Thrips are spindle-shaped, 1.2 mm or less in length and are yellow, amber, brown, or black. Adults have two pairs of wings which are fringed and have brown crossbands.

Figure 7. Twospotted spider mites are tiny (almost microscopic),

Figure 7. Twospotted spider mites are tiny (almost microscopic), pale to dark green, and have two or four darkly colored spots. Adults and nymphs have eight legs.

Figure 8. Corn earworms are green, reddish or brown with pale lo

Figure 8. Corn earworms are green, reddish or brown with pale longitudinal stripes and scattered black spots.

Figure 9. European corn borers are grayish pink with a dark head

Figure 9. European corn borers are grayish pink with a dark head and rows of small brown doughnut-shaped spots on the back.

Figure 10A-B. Cowpea curculio adults are black humpbacked weevil

Figure 10A-B. Cowpea curculio adults are black humpbacked weevils 6 to 7 mm long. Larvae are pale yellow and have brown heads.

Figure 11A-B. Stink bug adults are green or brown shield-shaped

Figure 11A-B. Stink bug adults are green or brown shield-shaped insects up to 19 mm long; nymphs are pale green or green with orange and black markings.

Figure 12. Bean leaf beetle larva are whitish larva (up to 10 mm

Figure 12. Bean leaf beetle larva are whitish larva (up to 10 mm long), dark at both ends and have three pairs of prolegs near the head.

Figure 13. The lesser cornstalk borer is a slender, bluish-green

Figure 13. The lesser cornstalk borer is a slender, bluish-green caterpillar up to 19 mm long and has brown rings around the body, three pairs of legs near the head, and five pairs of prolegs on the abdomen.

Figure 14. The limabean vine borer is gray when young and later

Figure 14. The limabean vine borer is gray when young and later becomes bluish-green and sparsely covered with long yellowish hairs. The caterpillars grow up to 25mm long and have three pairs of legs near the head and five pairs of prolegs on the abdomen.

Figure 15. Seedcorn maggots are white to yellow-white maggots up

Figure 15. Seedcorn maggots are white to yellow-white maggots up to 7 mm long.

Figure D. Leaffooted bug.

Figure D. Leaffooted bug.

Figure E. Leafhopper damage to beans.

Figure E. Leafhopper damage to beans.

Figure I. Stink bug nymph and adult.

Figure I. Stink bug nymph and adult.

Bean and Cowpea Aphids

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Bean aphid, Aphis fabae Scopoli, Aphididae, HEMIPTERA
Cowpea aphid, Aphis craccivora Koch, Aphididae, HEMIPTERA

DESCRIPTION

Adult – These soft-bodied, pear-shaped insects have antennae which are shorter than their bodies and a pair of cornicles (tailpipe-like appendages). They may be winged or wingless but the wingless forms are most common. The bean aphid has a dark green to black body between 2 and 2.6 mm long with white appendages. The cowpea aphid has a shiny black body with white appendages and ranges from 1.5 to 2.5 mm long.

Egg – The egg stage probably does not occur in North Carolina.

Nymph – Though smaller than adults, nymphs resemble the wingless forms in shape. Bean aphid nymphs are green, the last instar having five to seven pairs of white spots on the back of its abdomen. Cowpea aphid nymphs are pale green to gray with a powdery coating.

BIOLOGY

Distribution – Bean and cowpea aphids occur in many temperate and subtropical regions of the world. In North America, the bean aphid can be found from New Brunswick to Florida and westward to California. The cowpea aphid has been reported in at least 28 scattered states and in three Canadian provinces.

Host Plants – A general feeder, the bean aphid infests a large number of fruit, vegetable, agronomic, and ornamental plants as well as many weeds. A few of its vegetable hosts include asparagus, broad and lima beans, carrot, celery, corn, cowpea, cucumber, eggplant, lettuce, onion, pea, pepper, potato, spinach, tomato, and turnip. In states where winters are more severe than here in North Carolina, the euonymus shrub serves as the primary winter host plant. In many southern states, weeds such as dock, lambsquarters, and shepherdspurse are favored summer hosts.

Host plants of the cowpea aphid include alfalfa, apple, carrot, cotton, cowpea, dandelion, dock, goldenrod, kidney bean, lambsquarters, lettuce, lima bean, pinto bean, peanut, pepperweed, pigweed, red clover, shepherdspurse, vetch, wheat, white sweet clover, and yellow sweet clover.

Damage – Congregating on lower leaf surfaces and on terminal buds, aphids extract plant sap. Leaves curl and pucker and seedling plants may become stunted and die. On lima bean, bean aphids attack terminal leaves, flower heads, and stems of pods. Infested plants develop yellow foliage, may become dwarfed and malformed, and lose vigor. A dark sooty mold often grows on the honeydew-coated surfaces of aphid-infested plants.

Feeding and reproduction increase with warm weather in spring. Wingless female adults, known as "stem mothers," give birth to about 80 nymphs over a 212 week period. At temperatures of about 11.5°C (53°F), nymphs develop into adults in about 22 days. At warmer temperatures of about 28.5°C (83°F), development takes only 5 days. Most nymphs mature into wingless females, but periodically, winged females develop and migrate to new host plants. These adults produce offspring like theie wingless counterparts and thereby colonize new plants. Reproduction continues throughout the winter at a reduced rate and many generations are produced each year. Cowpea aphids have a similar life history though rates of development may vary.

Lady beetles and their larvae, lacewing larvae, syrphid fly larvae, and stilt bugs all feed on aphids. During periods of high humidity, fungus diseases also reduce populations.

CONTROL

For up-to-date chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Aphids. A-B. Bean aphids. C. Cowpea aphid.

Aphids. A-B. Bean aphids. C. Cowpea aphid.

Brown Leaf Beetle

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Bean leaf beetle, Cerotoma trifurcata (Forster), Chrysomelidae, COLEOPTERA

DESCRIPTION

Adult – Though the adult varies greatly in color and markings, it is typical reddish-brown to yellow with black margins and about 5 to 6 mm long. Each wing cover usually, but not always, is marked with three black spots. All bean leaf beetles, however, have a black triangular-shaped spot on the forward margin of the wings.

Egg – The lemon-shaped egg is orange and about 0.85 mm long.

Larva – The larva is basically whitish with both ends colored dark brown. Conspicuously segmented, it has three pairs of legs near the head. It grows to a length of about 10 mm.

Pupa – The pupa is exposed, white, soft-bodied, and about 5 mm long.

BIOLOGY

Distribution – The bean leaf beetle is abundant in the southeastern states particularly in the coastal counties. Its range, however, extends into Canada, New York, Minnesota, Kansas, Texas, and New Mexico. The insect appears to prefer poorly drained clay and organic soils.

Host Plants – Hosts of the bean leaf beetle include bean, clover, corn, cowpea, soybean, peanut, and several leguminous weeds.

Damage – Damage to bean, pea, and cowpea is caused primarily by the foliar-feeding adults. Bean leaf beetles prefer the youngest plant tissue available; when vegetative growth terminates, they will consume tender pod tissue. Pod damage is usually limited to outer layers of pod, developing beans themselves being infrequently attacked. In North Carolina, these beetles damage leaves and stems from late May through September. In addition to the beetles' direct attack, adults are also known vectors of the bean pod mottle, cowpea mosaic, and southern bean mosaic viruses. Bean leaf beetle larvae do a little damage by feeding on roots.

Life History – Adults overwinter in leaf litter or other vegetation, primarily in wooded areas. They become active in April and move to the earliest host plants available. In the southeastern United States, beetles usually do not attack beans or peas until mid-May. They feed voraciously for several days and then mate. Each female lays 175 to 250 eggs in clusters of 12 to 24 in the soil at the plant's base. Eggs hatch in 1 to 3 weeks, depending upon temperature. Larvae find their way to the base of the stem or roots and feed there for 3 to 6 weeks. Mature larvae form earthen cells within which the pupae form. In southern states, peak periods of adult activity generally occur the last of May, the last of July, the second and third weeks in August, and the second and third weeks of September. Second generation beetles overwinter in North Carolina.

CONTROL

Chemical control consists of applying foliar insecticides or using a granular insecticide in furrow at planting. Control practices for the Mexican bean beetle will control the bean leaf beetle.

For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Bean leaf beetle. A-B. Adults. C. Egg. D. Larva. E. Pupa.

Bean leaf beetle. A-B. Adults. C. Egg. D. Larva. E. Pupa.

Cowpea Curculio

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Cowpea curculio, Chalcodermus aeneus Boheman, Curculionidae, COLEOPTERA

DESCRIPTION

Adult – This black weevil is humpbacked, slightly tinged with bronze, and 6 to 7 mm long (Figure C).

Egg – Each oval egg is slightly less than 1 mm long. Translucent when first laid, it becomes an opaque white before hatching.

Larva – This pale yellow, brown-headed grub is legless. It is 6 to 7 mm long when fully grown.

Pupa – The pale yellow pupa, about 5 mm long, darkens as it matures. Its shape is similar to that of the adult.

BIOLOGY

Distribution – In the United States, the cowpea curculio is most common throughout the South Atlantic and Gulf Coast States. It has been reported as far north as Maryland and Iowa, as far west as Texas and Oklahoma, and as far south as Mexico and parts of South America.

Host Plants – The cowpea curculio infests field peas, stringbeans, soybean, lima bean, cotton, and strawberry. Black-eyed pea and crowder pea are most commonly attacked. Several leguminous weeds, including vetch, are also hosts.

Life History – Cowpea curculio adults pass the winter in crop refuse or weeds, particularly brown sedge, around previously infested plants. The black humpbacked snout beetles, or weevils, leave their overwintering sites from April through July. Weevils puncture developing pods with their snouts as they feed. Females lay a single egg in some of the feeding wounds. About 4 days later, brown-headed grubs emerge and infest the seeds of beans and peas. After feeding for 2 or 3 weeks, grubs chew exit holes through the pods, drop to the ground, bore into the soil and pupate. All grubs usually leave the pods within 7 days of each other. Approximately 10 days later, a new generation of adults emerge. There are two overlapping generations each year in North Carolina.

CONTROL

Late peas or beans isolated from earlier plantings are not likely to be severely infested by the cowpea curculio. Periods of hot, dry weather also reduce the level of damage by this pest. Since this weevil migrates by crawling or flying, crop rotation and sanitation measures are valuable in controlling this pest.

Chemical control of the cowpea curculio is necessary in the commercial production of beans and southern peas. An insecticide should be applied when blooms first appear and repeated at 5-day intervals as needed. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Cowpea curculio. A. Adult. B. Egg. C. Larva. D. Front view of la

Cowpea curculio. A. Adult. B. Egg. C. Larva. D. Front view of larval head. E. Pupa. F. Infested bean. G. Infested bean opened to show larva. H. Infested pod.

Figure C. Cowpea curculio.

Figure C. Cowpea curculio.

Lesser Cornstalk Borer

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Lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), Pyralidae, LEPIDOPTERA

DESCRIPTION

Adult – The moth has a wingspan of nearly 25.5 mm. The male's front wings are brownish-yellow and have grayish margins with several dark spots. The female's front wings are nearly black.

Egg – The egg is greenish-white and less than 1 mm in diameter.

Larva – The larva is a slender, bluish-green, brown-striped caterpillar about 19 mm long.

Pupa – The pupa is brownish and about 8.5 mm long.

BIOLOGY

Distribution – Though the lesser cornstalk borer is found from Maine to southern California, the bulk of its damage occurs in the southern states, particularly Alabama, Georgia, and South Carolina. It is also found in Mexico, Central America, and South America.

Host Plants – The lesser cornstalk borer prefers corn and legumes, but it also feeds on bean, cowpea, crabgrass, johnsongrass, pea, peanut, sorghum, soybean, and wheat.

Damage – Larvae of this small moth have been sporadically injurious to seedlings of many plant species and seem to be on the increase in the South. Injury is caused when a larva bores into the stalk of a host plant, thereby disrupting the growing point. Damage can be slight, or it can kill the plant. Damage is most prevalent in crops grown on sandy soils during dry conditions.

Life History – Lesser cornstalk borers hibernate as larvae or pupae. In North Carolina, they usually overwinter as larvae which develop into pupae before spring. Moths emerge early in spring and lay eggs on or near the host's leaves or stems. Eggs hatch in 2 to 7 days. Larvae feed first on leaves or roots of peanuts. On peas, the larvae tunnel up the main stems causing them to wilt. They can seldom penetrate older stems, however. Later they construct underground silken tubes or burrows from which they bore into plants near the ground line. They become full grown in 2 to 3 weeks, leave their burrows, and spin silken cocoons under trash on the surface of the ground. In these cocoons, they change to pupae from which moths emerge in 2 to 3 weeks. Two generations are known to occur in the mid-Atlantic States; three generations occur in South Carolina; and four generations occur in south Georgia and Florida.

CONTROL

Cultural practices, such as clean cultivation and weed destruction along fence rows, have long been recommended for lesser cornstalk borer control. Recent research findings in Georgia, however, indicate that cultivation promotes, not retards, injury by this insect on corn. The fact that damage by lesser cornstalk borer is rare under no-tillage cropping systems has been attributed to higher soil moisture and to the fact that larvae feed on old crop residue. Under conventional cropping systems, the cultural practice of late fall plowing may still be of some benefit since it kills overwintering life stages. For up-to-date chemical control recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Lesser cornstalk borer. A-B. Adults. C. Egg. D-E. Larva. F. Pupa

Lesser cornstalk borer. A-B. Adults. C. Egg. D-E. Larva. F. Pupa.

Limabean Vine Borer

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Limabean vine borer, Monoptilota pergratialis (Hulst), Pyralidae, LEPIDOPTERA

DESCRIPTION

Adult – This brownish-gray moth has whitish scales on the edge and across the end of its forewings. The forewings are marked with small black streaks and are black along the veins. Hind wings and the outer edges of the forewings have a brownish-gray fringe-like border. Male's hind wings are white, while the female's are more grayish. The wingspan is 21 to 23 mm.

Egg – The dull gray oblong-oval egg is 0.7 mm long and 0.4 mm wide.

Larva – Gray when very small, the larva gradually becomes bluish-green and sparsely covered with long yellow hairs (Figure F). Behind the black or brown head capsule is a yellowish-brown prothoracic shield. When fully grown, this caterpillar is 18 to 25 mm long.

Pupa – The yellowish to reddish-brown pupa is 12 to 14 mm long and is enclosed in a 16 mm long cocoon.

BIOLOGY

Distribution – Although this pest occurs throughout much of the east central and southeastern United States, it is primarily a problem along the Coastal Plain from Delaware and Maryland south to Florida and west to Alabama. The limabean vine borer also occurs in some southwestern states like Arizona.

Host Plants – This pest heavily infests pole and lima beans. Though its occurrence on other hosts is rare, this caterpillar has been reared on snap bean, cowpea, and dahlia. Large stemmed bean varieties are preferred.

Damage – Young larvae feed on leaves, slightly skinning the lower epidermis and leaving tell-tale frass, webbing, or excrement behind. As larvae mature, they bore into stems, typically just above or below nodes, and hollow out cavities. As a result, infested stems gradually swell and form galls up to 70 mm long and 20 mm in circumference. The galls eventually turn brown and develop a woody texture. Short, loose, silky frass tubes are attached to the entrance holes on the galls. Usually, infested plants are weakened and have lower yields. When galls are located near the tips of small stalks, the tops of plants often wilt and full-sized pods cannot be produced. The extent of damage varies with the position of the gall and the vigor of the host plant.

Life History – Limabean vine borers overwinter as prepupae on or near the soil surface. Moths emerge from late April to mid-May in eastern North Carolina and deposit eggs on leaves or in naturally occurring depressions in host plant stems. Two to 6 days later, eggs hatch and larvae begin feeding on leaves. After feeding for 4 to 7 days, larvae bore into stems where they continue feeding and complete their development. When fully grown, larvae bore exit holes in the galls, drop to the ground and enter the soil where they spin cocoons and pupate. A new generation of moths emerges about 15 days later. Larvae usually can be found from May through October. Later in the season, larvae may take over galls formed by previous generations instead of creating their own. In North Carolina, approximately three generations occur each year.

CONTROL

Hand removal of galls does more harm than good to infested plants. Fall plowing or winter cultivation helps reduce populations by destroying overwintering prepupae. Where practical, crop rotation is recommended. Foliar sprays to control this pest should begin when pods start to form. For up-to-date chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Limabean vine borer. A-B. Adult. C-D. Larvae. E. Cocoon. F. Dama

Limabean vine borer. A-B. Adult. C-D. Larvae. E. Cocoon. F. Damage.

Figure F. Limabean viner borer (left) and gall.

Figure F. Limabean viner borer (left) and gall.

Mexican Bean Beetle

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Mexican bean beetle, Epilachna varivestis Mulsant, Coccinellidae, COLEOPTERA

DESCRIPTION

Adult – This copper red beetle is 6 to 8.5 mm long and dome shaped (Figure G). Overwintering beetles are lighter in color. Each wing cover has eight small black spots that form three rows across the body when the wings are at rest.

Egg – The yellow egg is about 1.3 mm long and elliptical in shape.

Larva – The mature yellow larva is about 8.5 mm long and covered with dark, branched spines.

Pupa – The yellow- to copper-colored pupa is about 6 mm long. It moves very little and has fewer spines than the larva.

BIOLOGY

Distribution – Formerly, the Mexican bean beetle was limited from Colorado southward. It is now common throughout the United States with the exception of the Pacific coast states.

Host Plants – Mexican bean beetles have a wide host range. They are most commonly encountered on garden and field beans as well as cowpea. Soybean, clover, alfalfa, and closely related weeds may also be attacked.

Damage – The Mexican bean beetle is the most injurious pest of beans (snap, lima, pole, kidney, pinto, navy, bush). If overwintering populations are high, seedling damage may occur, though economic damage usually does not occur before August. Both larvae and adults feed on leaves, leaving the upper surface intact. Damaged plants have a characteristic lace-like (skeletonized) appearance. These remaining tissues die in about 2 days and turn brown, often giving the entire field a "burnt" cast. Pods and stems are often attacked, and shredded plants may die before any crop is matured.

Life History – Adult beetles overwinter in hedgerows, ditchbanks, and woodlands and may attack plants soon after seedlings emerge in spring. Most beetles leave their winter quarters over a 2-month period. Following feeding, adult females deposit eggs in clusters of 40 or more on the undersurface of leaves. Eggs hatch in 5 to 14 days and larvae continue to feed for 2 to 5 weeks. Larvae pupate on leaves and adults emerge after about 10 days. Adults feed, mate, and lay eggs over a period of 2 weeks. Generation time from egg to adult is about 30 days. In North Carolina, there are three or four generations each year.

CONTROL

Snap bean varieties such as Wade, Logan, and Black Valentine are generally less severely damaged than other varieties by the Mexican bean beetle. Since damage is usually most severe during July and August, very early maturing bean varieties and fall plantings may be grown with little injury. Prompt removal of pods and destruction of old plants are suggested as insurance against population buildup. An extensive parasite release program is operational in the Delmarva Peninsula.

Chemical control consists of applying foliar insecticides to the undersides of leaves or using a granular insecticide in furrow at planting. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Mexican bean beetle. A-B. Adults. C. Eggs. D. Larvae. E. Pupa.

Mexican bean beetle. A-B. Adults. C. Eggs. D. Larvae. E. Pupa.

Figure G. Mexican bean beetle with larva, pupa, and eggs.

Figure G. Mexican bean beetle with larva, pupa, and eggs.

Pea Aphid

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Pea aphid, Acyrthosiphon pisum (Harris), Aphididae, HEMIPTERA

DESCRIPTION

Adult – The pea aphid adult is long-legged, light to deep green with reddish eyes. It has a body length of 2.0 to 4.0 mm though a winged individual may be as long as 4.5 mm from its head to the tip of its wings. Cornicles (a pair of tailpipe-like structures projecting from the abdomen) of this aphid are characteristically long and slender.

Egg – Approximately 0.85 mm long, the light green egg turns a shiny black before hatching. The egg stage does not occur in North Carolina.

Nymph – The immature aphid is smaller than but similar to the larger wingless adult. It requires four molts to reach the adult stage.

BIOLOGY

Distribution – The pea aphid is found throughout the United States and Canada wherever peas, English peas, and alfalfa are grown.

Host Plants – Pea aphids infest garden, field, and sweet peas, sweet clover, alfalfa, and some leguminous weeds. Vetch and crimson clover are important overwintering hosts.

Damage – Pea aphids extract sap from the terminal leaves and stem of the host plant. They also feed on pods causing them to curl, shrink, and partially fill. Their feeding can result in deformation, wilting, or death of the host depending upon the infestation level and size of the plant. Plants less than 15 cm (6 in) high are easily killed by a few aphids, whereas larger plants are only slightly damaged. Plants are often coated with shiny honeydew secreted by aphids, and cast skins may give leaves and ground a whitish appearance. These aphids also transmit pea enation mosaic and yellow bean mosaic viruses. The first of these viruses, pea enation mosaic, has been a problem in New York but has not been reported in North Carolina.

Life History – In North Carolina, wingless female pea aphids continue to feed and breed throughout the winter months. In spring, aphid activity increases. Each adult female gives birth to 10 to 14 nymphs each day until she has produced about 100 offspring. Nymphs mature into adults in 10 to 14 days. Most nymphs develop into wingless female adults. However, when overcrowding occurs, winged aphids develop, migrate to other host plants, and establish new colonies. Since generations overlap and reproduction continues all year, the number of annual generations is difficult to determine. The pea aphid thrives best and reproduces most rapidly at temperatures around 18°C (65°F) and humidities near 80 percent.

CONTROL

For up-to-date chemical control recommendations, consult the current North Carolina Agricultural Chemical Manual.

Pea aphid. A-B. Winged adults. C. Wingless adult. D. Nymph.

Pea aphid. A-B. Winged adults. C. Wingless adult. D. Nymph.

Seedcorn Maggot

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Seedcorn maggot, Hylemya platura (Meigen), Anthomyiidae, DIPTERA

DESCRIPTION

Adult – This gray, black-legged fly has scattered bristles on its body and is approximately 5 mm long.

Egg – Each white elongate egg has a rough surface and is about 1 mm in length.

Larva – This 12-segmented, white to yellow-white maggot is 5 to 7 mm long when mature. It is legless and tough skinned with a sharply pointed head and a rounded tail.

Pupa – The last larval skin hardens to form a puparium (about 5 mm long) in which the pupa develops. The ivory puparium gradually turns reddish-brown as the pupa matures.

BIOLOGY

Distribution – Common throughout the temperate zones of the world, the seedcorn maggot is found in all arable portions of North America from southern Canada into Mexico. It has not been found at altitudes above 1.4 km (4500 feet). This pest is usually a problem during cold, wet seasons and on land high in organic matter.

Host Plants – Although it feeds primarily on decaying organic matter, the seedcorn maggot infests roots and / or seeds of more than 47 kinds of plants. In North Carolina, it is a pest of bean, pea, cucumber, melons, onion, corn, pepper, potato, and other vegetable crops.

Damage – Seedcorn maggots damage newly planted seeds by feeding on seed contents often leaving empty shells and resulting in poor germination. Seedlings which do emerge are tall and spindly with few leaves. They rarely mature or mature late because of poor seed quality. Occasionally, seedcorn maggots tunnel in seedling stems. Either type of feeding allows entry of disease-causing organisms.

Life History – In North Carolina, all stages of the seedcorn maggot can be found throughout the winter. Further north, however, these insects overwinter in the soil as pupae. Adult flies emerge from puparia at night or early in the morning and push themselves up to the soil surface. For a variable length of time, adults feed on nectar and honeydew. At the end of this period, each fertilized female begins laying an average of 270 eggs, singly or in small clusters, in moist soil. Freshly distributed soil, fields with decaying seed or crop remnants, and/or organically fertilized soils are all attractive to ovipositing female flies.

Eggs hatch in 7 to 9 days depending on temperature. Newly hatched larvae tunnel in seeds or other decaying vegetable matter. Maggots remain active at temperatures as low as 4.4°C (40°F). They develop through three larval stages. After feeding for 1 to 3 weeks, the larvae burrow as deep as 18 cm in the soil to pupate. Pupation may last 7 to 26 days or all winter.

In the eastern United States, three to five generations of seedcorn maggots develop each year. Generations which occur during spring and fall are the most abundant and destructive. During summer, only a limited number of adults survive.

CONTROL

For control of seedcorn maggots in field or vegetable crops, shallow planting in a well-prepared seedbed, sufficiently late for quick seed germination, is one means of preventing injury. Land where manure is heavy or where a cover crop is turned under should be plowed early in the fall, if possible. This renders the field less attractive to egg-laying flies the following spring. Prompt resetting or replanting of damaged crops usually gives a good stand.

Combination fungicide-insecticide seed treatments or soil-applied insecticides can be used to prevent seedcorn maggot damage. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Seedcorn maggot. A-B. Adults. C. Maggot. D. Puparium.

Seedcorn maggot. A-B. Adults. C. Maggot. D. Puparium.

Figure EE. Seedcorn maggot on corn seed (right) and on bean root

Figure EE. Seedcorn maggot on corn seed (right) and on bean roots.

Flower thrips, Frankliniella tritici (Fitch), Thripidae, THYSANOPTERA
Soybean thrips, Sericothrips variabilis (Beach), Thripidae, THYSANOPTERA
Tobacco thrips, Frankliniella fusca (Hinds), Thripidae, THYSANOPTERA

DESCRIPTION

Adult – Thrips are 1.25 mm or less in length and have two pairs of long, narrow wings fringed with long hairs. The flower thrips is yellowish-brown to amber with an orange thorax. The soybean thrips has a yellow body with a dark blotch on the thorax and two distinct crossbands on the forewings. The tobacco thrips is dark brown or black.

Egg – About 0.2 mm long, thrips eggs are cylindrical and slightly kidney shaped with a smooth white or yellow surface.

Larva – The two larval instars range from 0.6 to 1.0 mm long. Larvae are white when newly hatched, then gradually turn yellow with age. The soybean thrips' larva eventually turn orange with some red pigmentation, though the body sometimes has a greenish tint due to ingested chlorophyll.

Prepupa and Pupa – Pupal stages resemble larvae in shape and color but have short (prepupae) to long (pupae) wing pads. The prepupa is about 1.2 mm long and shrinks to about 1.0 mm as it becomes a pupa. The pupa usually remains motionless unless disturbed.

BIOLOGY

Distribution – All three thrips species are common throughout the eastern United States. Soybean thrips also occur in California, Arizona, Utah, and Texas. Flower thrips migrate in frontal wind systems, especially in June.

Host Plants – Flower and tobacco thrips have been collected from many plant orders, including a wide range of flowers, trees, grasses, field crops, vegetables, vines, and weeds. Flower thrips seem to prefer grasses and yellow or other lightly colored blossoms. Soybean thrips feed primarily on soybean, bean, and other legumes, but also infest cotton, cucumber, smartweed, and a number of grasses.

Damage – Among damaging thrips species, soybean thrips have been ranked ninth in economic importance, yet they are relatively minor pests. These thrips feed on the underside of bean and soybean leaves throughout the growing season reaching maximum densities about a month after planting. Six to 10 thrips per leaf may cause some yellowing but relatively little economic damage. Early season drought may cause an ordinarily harmless thrips population to become a problem. Thrips damage occurs primarily during periods of vegetative growth and is difficult to distinguish from that of a wide range of pests and diseases which cause yellowing and browning of leaves in late summer. On soybeans, populations of 30 to 60 thrips per leaf have been reported to cause substantial injury.

Life History – In North Carolina, thrips overwinter as hibernating adults in sheltered areas, as larvae on plants or as pupae in the soil. They resume development in spring. Adults emerge and fly in search of suitable host plants. Though weak fliers, adult thrips are capable of flying from plant to plant and may be carried long distances by wind.

The number of eggs laid by each female soybean thrips has not been determined, but most species of thrips insert 10 to 100 eggs, singly, into plant tissue. About 4 days later, eggs hatch. At temperatures of 22°C (72°F), larvae feed for about 7 days on the underside of leaves, often hiding near large leaf veins. Mature second instar larvae drop to the soil and make chambers in the center of small dirt clods. Here they turn into quiescent nonfeeding prepupae. The next day prepupae transform into pupae. About 3 days later a new generation of adults emerges. Most thrips species complete five or more generations in North Carolina.

Though soybean thrips develop most rapidly at temperatures of 32°C (90°F), 26°C (78°F) is considered optimum for their development because at this temperature, thrips mortality is lowest. In addition to temperature, several predators have an effect on the size of thrips populations. These include a cocoon-spinning thrips, Aeolothrips fasciatus (Linnaeus) (about 1.5 mm long, dark as an adult, yellow as a larva), the insidious plant bug, Orius insidiosus (Say) (a tiny chinch-bug-like insect), and several phytoseiid mites.

CONTROL

For up-to-date chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual.

Thrips. A. Flower thrips. B. Soybean thrips. C. Tobacco thrips.

Thrips. A. Flower thrips. B. Soybean thrips. C. Tobacco thrips. D. Thrips damage.

Twospotted Spider Mite

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Twospotted spider mite, Tetranychus urticae Koch, Tetranychidae, PROSTIGMATA

DESCRIPTION

Adult – The eight-legged adult is almost microscopic, being only 0.3 to 0.5 mm long. Oval in shape, the active summer female is yellowish to dark green with two or four dark dorsal spots. Smaller and more active than the female, the male has a narrower body and a more pointed abdomen.

Egg – The egg is spherical, minute and transparent when first deposited. It gradually assumes a yellowish-green color.

Larva – The six-legged larva, not much bigger than the egg, is colorless except for carmine eyes.

Nymph – The two nymphal stages are difficult to distinguish. Both are pale green, oval, and eight-legged. The pair of dark spots is visible at this point of development.

BIOLOGY

Distribution – Twospotted spider mites are widely distributed throughout the world. In the southeastern United States, they are pests throughout the Coastal Plain area.

Host Plants – Twospotted spider mites have been found on more than 180 host plants, including at least 100 cultivated species. Violets, chickweed, pokeweed, wild mustard, hairy vetch, red clover, Carolina geranium, and blackberry are common hosts from which infestations spread to crops nearby.

Damage – Mites pierce the epidermis and extract sap from the undersides of leaves. Infested foliage soon assumes a whitish or bronze appearance. Lightly infested leaves have pale blotches or spots showing through the leaf; heavily infested leaves turn completely pale and dry up. The undersurfaces of leaves usually are covered with silken webs over which the mites crawl. Heavily infested plants may have webs all over them. Close examination reveals adult mites on the leaves, but the larvae initiate damage.

Life History – Twospotted spider mites overwinter as females resistant to low temperatures. These females are red as opposed to the active summer forms which are yellowish-green. In greenhouses or during mild winters, some feeding and egg-laying activities may continue.

In warm weather, egg-laying activities increase; each female produces up to 19 eggs per day and up to 100 eggs in all. The number of eggs laid depends largely on temperature. After an incubation period of 3 to 19 days, six-legged larvae hatch from the eggs and feed. Immature mites go through a resting period between the larval and nymphal stages and again after each of the two nymphal instars. The mites may mature into adults in as few as 5 days or as many as 20, depending on temperature. Development is most rapid during hot, dry weather. Many generations are produced each year.

CONTROL

One form of cultural control is the destruction of weeds around the field in fall or early spring. This practice reduces the overwintering population. Destruction of weeds along fence rows or around the edges of fields during the growing season is not advisable. Such weed control forces mites to migrate into the field. The tomato variety Campbell 135 is highly resistant to twospotted spider mites.

Spider mites are distributed over a field in two ways: (1) migration of females from a heavily infested area to a lightly infested one, and (2) natural or mechanical transportation of mites (by wind, mammals, and man) from an infested area to an uninfested one. Consequently, known "hot spots" should be investigated last, not first when entering the field.

Several miticides provide effective chemical control. A second application is often advised 5 to 7 days after the first. For recommended miticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

Stages of twospotted spider mites.

Stages of twospotted spider mites.

Authors

Extension Specialist (Fruits & Vegetables)
Entomology and Plant Pathology
Professor Emeritus
Entomology and Plant Pathology
Retired Extension Specialist (Identification & Diagnosis)
Entomology and Plant Pathology

Publication date: Feb. 10, 2003
AG-295

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