Key to Tomato Pests
Tomatoes are subject to attack by a large number of insect pests from the time plants first emerge in the seed bed until harvest. Aphids, flea beetles, leafminers, and spider mites threaten young plant-bed tomatoes. In the field, flea beetles, aphids, leafminers, stink bugs, and fruitworms cause minimal damage to the foliage. However, severe damage may result either from their feeding on the fruit or by spreading certain diseases.
Greenhouse tomatoes have many of the same pests as field tomatoes. Tiny pests such as aphids, whiteflies, leafminers, and spider mites are more likely to infest greenhouse crops than beetles, grubs, or caterpillars. Occasionally moths enter through holes in screens or fans and lay eggs in the greenhouse. Even in screened greenhouses, armyworms, fruitworms, and loopers may be brought into the greenhouses on plants.
A. Pests that feed on the upper plant
- Pests that mine leaves or bore into fruits and / or buds
- Tomato fruitworm – Early instars: cream colored or yellowish-green with few markings; later instars: green, reddish, or brown with pale stripes and scattered black spots; moderately hairy; up to 44 mm long; 3 pairs of legs, 5 pairs of prolegs (Figure 1); holes are chewed in fruits and buds
- Tobacco budworm – This caterpillar is similar to the tomato fruitworm except mature worms are somewhat smaller and slightly more slender than tomato fruitworms (Figure 2); in addition, the microscopic spines on the skin of tobacco budworms are more slender, longer, and occur closer to the setae (hairs)
- Tomato pinworm – Young yellowish-gray larva only a few millimeters long, making blotch mines in leaves; older yellow, green, or gray, purple-spotted larva up to 8 mm long (Figure 3), folding leaves and webbing them together, or boring into stems, buds, and fruit; fruits with pinholes and discolored blotches
- Vegetable leafminer – Colorless to bright yellow maggot, up to 3 mm long, with pointed head; makes serpentine mines in leaves; each mine slightly enlarged at one end (Figure 4)
- Chewing pests that make holes in leaves
- Blister beetles – Several species of slender, elongate beetles up to 19 mm long; have prominent heads; bodies variously colored but usually black (Figure 5A), black with yellow margins (Figue 5B), or black and yellow striped (Figure 5C); stringy black excrement on heavily infested plants; foliage ragged; plants sometimes stunted
- Cabbage looper – Green caterpillar with longitudinal white stripes; body up to 30 mm long, tapers toward the head; 3 pairs of legs near head; 3 pairs of fleshy prolegs (Figure 6); young larva on underside of leaf; consumes tender leaf tissue leaving most veins intact
- Colorado potato beetle – Yellowish-brown, oval, convex beetle up to 14 mm long with 5 black longitudinal stripes on each wing cover and several black spots on the pronotum (area behind the head) (Figure 7); feeds on leaves and terminal growth
- Flea beetles – Various species of tiny, darkly colored beetles 2.5 to 4.5 mm long; have solid color body or black body with pale yellow stripe on each wing cover (Figure 8); tiny round holes in foliage
- Hornworms – Green to reddish-brown caterpillars up to 90 mm long with red or black anal horn; body with 7 diagonal or 8 V-shaped marks on each side; round black spiracles along side of body (Figure 9); strips leaves from vines; infrequently feeds on fruit leaving large, open superficial scars
- Sap-sucking pests which cause leaf discoloration, leaf or fruit deformation, or defoliation
- Aphids – Soft-bodied, pear-shaped insects with a pair of dark cornicles and a cauda protruding from the abdomen; may be winged or wingless -- wingless forms most common; feed in colonies; cause discoloration or mottling of the foliage; excrete honeydew on which sooty mold grows
- Green peach aphid – Pale yellow to green wingless adult up to 2.4 mm long (Figure 10A); winged adult with dark dorsal blotch on yellowish-green body (Figure 10B); nymph with 3 dark lines on abdomen (Figure 10C)
- Potato aphid – Adult and nymph both solid pink, green and pink mottled or light green with dark stripe; adult up to 3.5 mm long; long, slender cornicles about twice as long as cauda (Figure 11)
- Greenhouse whitefly – White moth-like insect about 1.5 mm long; found in conjunction with tiny yellow crawlers and / or green, oval, flattened, immobile nymphs and pupae (Figure 12); leaves yellow and drop from plant; some plants stunted and unreproductive; black sooty mold often present on leaves
- Stink bug – Green or brown (nymph green with orange and black markings) shield-shaped insect; adult up to 19 mm long (Figure 13); pierces buds and fruit causing buds to drop and fruit to be deformed
- Silverleaf whitefly – Adult is slightly smaller (0.96 mm in the female and 0.82 mm in the male), slightly more yellow in color and holds its wings roof-like at about a 45-degree angle; nymphs appear glassy to opaque yellowish and have a flattened and scale-like body with the margin near the leaf surface; pupa is flattened, dome-shaped and lack setae (Figure 14); plants stunted and nonreproductive with black sooty mold present
- Western flower thrips – Adult is about 1 mm long, varies from a pale yellow to dark brown and has a rounded, narrow abdomen; larvae are distinctly yellow; plants are distorted and have a silvery appearance (Figure 15); an important vector of spotted wilt virus
- Aphids – Soft-bodied, pear-shaped insects with a pair of dark cornicles and a cauda protruding from the abdomen; may be winged or wingless -- wingless forms most common; feed in colonies; cause discoloration or mottling of the foliage; excrete honeydew on which sooty mold grows
B. Pests that feed on roots or lower stems
- Cutworm – Fat, basically gray, brown, or black caterpillar 40 to 50 mm long when fully grown; 3 pairs of legs near head; 5 pairs of fleshy prolegs (Figure 16); active at night; young caterpillar climbs on leaves, older caterpillar severs seedling stems near the ground; hides during the day in soil burrows at the bases of plants
- Southern potato wireworm – Slender, wire-like cylindrical larva with 3 pairs of short legs near the head and a pair of fleshy anal prolegs; white, cream, or yellow-gray body with red-orange head capsule; about 17 mm long when fully grown; closed notch in last abdominal segment (Figure 17); ragged, irregular holes in root
Black cutworm, Agrotis ipsilon (Hufnagel), Noctuidae, LEPIDOPTERA
Granulate cutworm, Feltia subterranea (Fabricius), Noctuidae, LEPIDOPTERA
Variegated cutworm, Peridroma saucia (Hubner), Noctuidae, LEPIDOPTERA
Adult – Black cutworm moths have dark brown forewings, light-colored hind wings, and a wing expanse of 38 to 51 mm. Granulate cutworm moths have yellowish-brown forewings and a wingspan of 38 to 45 mm. Variegated cutworm moths may be yellowish or brownish with a wingspan of 38 to 50 mm.
Egg – Cutworm eggs are white and usually laid singly or in small clusters. Variegated cutworm eggs are generally laid in elongate patches.
Larva – Black cutworm larvae are dark greasy gray to black with a light colored line down the center of the back. They are 38 to 45 mm long when mature and the skin is covered with smooth black granules. Granulate cutworm larvae are dusty brown with a more roughly granulate skin and 25 to 38 mm in length. Variegated cutworm larvae have a distinct pale yellow dot on the mid-dorsal line of each segment. About 50 mm long when mature, they are pale dirty brown in color.
Pupa – Cutworm pupae are about 20 mm in length and dark brown or mahogany in color.
Distribution – Cutworms are cosmopolitan in their distribution and are common in Canada and the United States. The black cutworm is more abundant in the northern portions of its range while the granulate cutworm is more abundant southward. In North Carolina, cutworms are generally more of a problem in the Coastal Plain.
Host Plants – Cutworms attack many field crops, grasses, and vegetable crops such as asparagus, bean, crucifers, cucurbits, corn, cowpea, lettuce, onion, pea, pepper, potato, spinach, sweet potato and tomato.
Damage – Several species of cutworms may injure vegetable seedlings and newly set plants in the field. Larvae hide under clods and in cracks in the soil by day and appear at night cutting off young plants near the ground and feeding on the foliage. The black cutworm is one of the most destructive cutworms. One larva often severs numerous plants in a row during a single night. Small populations can cause considerable injury resulting in the need to replant. The granulate cutworm and the mature variegated cutworm also sever plants. Early instars of the variegated cutworm, however, climb plants and feed on the leaves.
Life History – Cutworms pass the winter as larvae or pupae. In early spring, larvae which have overwintered resume activity and feed until they are mature. Pupation then takes place in the soil. Moths emerge from pupae 2 to 4 weeks later. Soon afterwards, females begin depositing eggs at night in clusters on the undersides of leaves. Each female lays hundreds of eggs. Under favorable, warm conditions, eggs hatch in 3 to 5 days.
Young larvae may feed on leaves, but larger larvae are most commonly found in the soil around the bases of plants. After feeding for 3 to 4 weeks and developing through 5 to 8 instars, larvae pupate in the soil. A new generation of moths soon emerges. Most cutworms complete 3 or 4 generations per year in North Carolina.
Since extensive damage may occur in a short period of time, plant beds and newly set plants should be inspected frequently. A bait may be used in infested plant beds or on newly set plants in the field. For up-to-date control recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Tomato fruitworm, Helicoverpa (Heliothis) zea (Boddie), Noctuidae, LEPIDOPTERA
Tobacco budworm, Heliothis virescens (Fabricius), Noctuidae, LEPIDOPTERA
Adult – The tomato fruitworm moth is usually light yellowish-olive with a single dark spot near the center of each forewing. Tobacco budworm moths are light olive to brownish-olive with a wingspan of 3.2 to 3.8 cm. Each forewing bears 3 slanted dark olive or brown bands. Hind wings are white with white borders.
Egg – Eggs of both species are similar in appearance. They are almost spherical with a flattened base, about 0.6 mm in diameter, and white or cream color. They develop a reddish-brown band just prior to hatch.
Larva – Both species are similar in appearance. Newly emerged larvae are yellowish-white with a brown head. Color varies from greenish-yellow and reddish-brown or even black with paler stripes running lengthwise on the body. The skin of the tobacco hornworm has microscopic spines which are longer and closer to the setae than those of the tomato fruitworm.
Pupa – Pupae of both species are typical for this family (Noctuidae). Shiny and reddish-brown at first, they become dark brown before adult emergence.
Distribution – Tomato fruitworm occurs throughout the Western Hemisphere extending as far north as Canada and as far south as Argentina. The tobacco budworm has a similar distribution but is more abundant in warmer regions, whereas the tomato fruitworm is more abundant in cooler regions. In North Carolina, fruitworms occur throughout the state but are generally more severe in the southern Coastal Plain.
Host Plants – The tomato fruitworm feeds on at least 16 cultivated plants. Corn is the most important host of the tomato fruitworm. The tobacco budworm does not infest corn, but both species are common on cotton and soybeans. Cotton, soybeans, tomatoes and tobacco are the only cultivated crop hosts of the tobacco budworm in North Carolina. Wild hosts include deergrass and toadflax.
Damage – Fruitworms, primarily the tomato fruitworm, feed on tomato leaves and fruit. Distorted leaves often result from feeding upon the tips of the leaves in the developing bud. Both species may also bore in stalks or midribs.
Life History – Fruitworms overwinter as pupae in the top 4 cm of soil. Tomato fruitworm adults emerge from early May to early June. Females generally emerge earlier than males. Tobacco budworm adults emerge in North Carolina from late April to mid-May. Eggs are deposited on the leaves or buds of tomato plants. After hatching, larvae may first feed on leaves and then move to buds or fruit. Tomato fruitworm larvae have 5 to 6 instars with the development period varying from 21 to 25 days. Tobacco budworm development is similar. Pupation occurs in the soil. Tomato fruitworm pupae enter diapause in August in North Carolina and tobacco budworms begin diapause in September. Both species have 4 generations per year in North Carolina.
The wasp parasite Campoletis sonorensis kills small tobacco budworms and another wasp parasite, Cardiochiles nigriceps, kills budworms in the prepupal stage. Predators include several Polistes paper wasps. Several diseases including the microsporidian Nosema heliothidis Lutz and Splendor also reduce budworm populations. For specific chemical control recommendations, see the current North Carolina Agricultural Chemicals Manual.
Greenhouse whitefly,Trialeurodes vaporariorum (Westwood), Aleyrodidae, HEMIPTERA
Adult – About 1.5 mm long, the adult is a white insect which resembles a tiny moth.
Egg – The oblong eggs, pale green to purple, are inserted into the lower leaf surface, often in a circle or a crescent. Each egg is about 0.2 mm long.
Nymph – The tiny, first instar nymph (or crawler) is yellow with red eyes and has functional legs and antennae. Second and third instar nymphs are flattened, immobile scale-like insects.
Pupa – About 0.75 mm long, the oval, flattened pupa is a pale green (normal) or black (parasitized) insect with long hairs on its back and around its body margin. After the adult has emerged, a white, almost transparent pupal skin is left behind.
Distribution – Greenhouse whiteflies are worldwide pests of greenhouse-grown ornamentals and vegetables. First discovered in England in 1856, the were found in the northeastern United States in 1870. Tropical Central or South America are suggested origins of the greenhouse whitefly.
Host Plants – Greenhouse whiteflies infest a wide variety of ornamental and vegetable crops, and they can survive outdoors during the growing season, particularly in sheltered locations. Some of the more important hosts include bean, melon, lettuce, cucumber, tomato, squash, potato, eggplant, strawberry, grape, tobacco, and rose. Even trees such as avocado may be infested.
Damage – Nymphs and adults extract plant sap through their needle-like mouthparts, the adults preferring to feed on tender new growth. As a result, leaves turn yellow and drop from infested plants. In addition to having an unthrifty appearance, plants may be stunted and unreproductive. Sooty mold often grows on leaves covered with honeydew secretions of whiteflies and interfere further with the growth of plants.
Life History – Greenhouse whiteflies reproduce relatively slowly (one generation every 30 to 45 days), but each female lays about 250 eggs and lives as long as two months. Adults usually are found on the lower surface of new leaves. There they insert their eggs which hatch 5 to 7 days later. New crawlers move about the plant for a day or two, often from leaf to leaf, before inserting their mouthparts to feed. Once this occurs, they probably do not move again until mature. The crawlers molt into later nymphal instars and then into pupae. Finally, a new generation of whitish-yellow adults emerges. They soon are covered with a white waxy bloom.
Parasitic wasps, Encarsia formosa, sometimes help keep greenhouse whitefly populations under control. However, at temperatures below 24°C (75°F), the reproduction of these parasites is inhibited. As a result, whitefly infestations are encouraged by lower greenhouse temperatures.
Control of whiteflies is difficult because the eggs and immature forms are resistant to many aerosol and insecticide sprays. One must make regular applications of pesticides to control emerging adults until the last of a whole generation of immature whiteflies has emerged. Methomyl and some of the synthetic pyrethroid and synthetic insect-growth-regulator pesticides, however, are extremely effective and need not be applied as often. For specific chemical control recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Tobacco hornworm, Manduca sexta (Linnaeus), Sphingidae, LEPIDOPTERA
Tomato hornworm, Manduca quinquemaculata (Haworth), Sphingidae, LEPIDOPTERA
Adult – Adult tobacco hornworm moths have a wingspan of about 112 to 127 mm and are slate brown compared to the ash gray color of tomato hornworms. Tobacco hornworms have 6 orange spots on each side of the abdomen, whereas tomato hornworms have 5 similar, but less distinct, spots on each side. Wavy lines on the hind wings of the tomato hornworm are more distinct and jagged than the lines on the hind wings of the tobacco hornworm moth.
Egg – Hornworm eggs are smooth, spherical, and about 1.3 mm in diameter. Light green at first, they turn white before hatching.
Larva – Mature tobacco hornworm larvae usually have green bodies with fine white pubescence and seven diagonal stripes on each side; the posterior horn is usually curved and red. Tomato hornworm larvae have 8 V-shared markings on each side; the horn is straight and black. Both species are about 75 to 85 mm long when fully grown.
Pupa – Pupae are brown, hard, spindle-shaped, and about 5 cm long. They have a curved, projecting, pitcher-handle-like tongue case. The tongue case of the tomato hornworm is longer and more curved than the tongue case of the tobacco hornworm.
Distribution – The tobacco hornworm ranges from southern Canada to Argentina. The range of the tomato hornworm, however, extends only from southern Canada through the southern United States.
Host Plants – Hornworms feed primarily on solanaceous plants. These hosts include tobacco, tomato, eggplant, pepper, and some weedy plants. Tobacco and tomato plants are preferred for oviposition.
Damage – Hornworms strip leaves from tomato vines. If a heavy infestation develops, caterpillars also feed on developing fruit. Rather than bore into fruit, they feed superficially leaving large open scars. Fruit damage, however, is much less common than defoliation. Hornworm damage usually begins to occur in midsummer and continues throughout the remainder of the growing season.
Life History – Hornworms overwinter in the soil as pupae. Moths of this overwintering generation begin to emerge in early June and may continue to emerge as late as August. Nocturnal in habit, hornworm moths frequently can be seen hovering over plants at dusk. At night, eggs are deposited on the underside of leaves. Each moth deposits one to 5 eggs per plant visit and may lay up to 2,000 eggs.
Hornworms emerge from the eggs about 4 days later, depending upon temperature. After feeding for 3 weeks, hornworms burrow into the soil and spend 4 days as prepupae. In summer, the pupal period lasts 3 weeks after which a new generation of moths emerges. Heavy egg deposition is common in August and early September. At least two generations occur each year in North Carolina.
In small gardens, hornworms can be controlled simply by picking the larvae off the plants. Most seasons, however, hornworms are kept at subeconomic levels by a wasp parasite. Parasitized hornworms are easily recognized by the small white oblong cocoons attached to their backs. Such worms should be left in the garden so the emerging wasps can parasitize other hornworms.
For chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Tomato pinworm, Keiferia lycopersicella (Walsingham), Gelechiidae, LEPIDOPTERA
Adult – The small gray moth has a reddish-brown, mottled head and thorax. Its body is about 6 mm long with a 9 to 12 mm wingspan.
Egg – The tiny oval egg is about 0.4 mm long. Light yellow when newly deposited, it turns pale orange before hatching.
Larva – The newly hatched larva is yellowish-gray and about 0.8 mm long. The mature fourth instar may be yellow, green, or ash gray and is covered with dark purple spots. Such a larva averages 6.5 mm long.
Pupa – A little over 6 mm long, the pupa gradually changes from green to brown. It occurs in the soil enclosed in a pupal cell made of loosely woven silk and covered with soil particles.
Distribution – This pest lives year round in the worm agricultural areas of Mexico, California, Texas, and Florida. The pinworm is primarily a greenhouse problem in Mississippi and states further north where it cannot overwinter outdoors. Even in these states, outdoor infestations occur but they usually are limited to fields near infested greenhouses.
Host Plants – The tomato pinworm feeds only on solanaceous plants. Common hosts include crops such as tomato, potato, and eggplant. The weeds nightshade and horsenettle are also subject to attack.
Damage – Blotch-like leaf mines, folded and tied leaves, pinholes in stems and fruit, and fruit blotches all can be caused by pinworms. First and second instar larvae mine leaves in a manner similar to that of serpentine and vegetable leafminers. These mines, however, are widened gradually into one large blotch.
Upon emerging from leaf mines, third instar larvae fold and web leaves to protect themselves and feed from inside these shelters. Some of the larvae bore into stems, buds, and fruit leaving small "pinholes" on the surface. The fruit usually is entered near calyx lobes or the stem. Larvae rarely penetrate deeper than 18 mm and usually feed just below the skin. In addition to the presence of pinholes, injured tomato fruits have discolored blotches. Damage to leaves and vines is of little importance, but injury to the fruit can cause a substantial loss.
Life History – In California, Florida, Texas, and Mexico, tomato pinworms overwinter outdoors as pupae at or near the soil surface. In North Carolina and most other states, pinworms spend winter in greenhouses. The nocturnal moths may emerge as early as March or April. Eggs, usually deposited on the undersides of leaves, hatch about one week later. During summer, larvae mine the leaves for about 6 days and then fold leaves or bore into fruit for another 6 days. Mature fourth instar larvae either remain in folded leaves or drop to the soil to pupate. About 12 days later, a new generation of moths emerges.
In summer, a generation can be completed every 26 to 34 days. In cooler weather, the life cycle is longer. Seven to 8 overlapping generations occur each year in Florida. It is probable that just as many occur in North Carolina greenhouses. If moths escape to the outside, several generations may occur in field tomatoes during summer.
Sanitation and prevention are good control measures for tomato pinworms. Infestations usually result from shipped in or local greenhouse-grown transplants. Therefore, close inspection of new plants can prevent serious problems later in the season. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Silverleaf whitefly, Bemisia argentifolii Bellows and Perring, Aleyrodidae, HOMOPTERA
Adult – The silverleaf whitefly is slightly smaller (about 0.96 mm in the female and 0.82 mm in the male) and slightly yellow than other whiteflies. The head is broad at the antennae and narrow toward the moth parts. The wings are held roof-like at about a 45 degree angle, whereas other whiteflies usually hold the wings nearly flat over the body. Hence the silverleaf whitefly appears more slender than other common whiteflies.
Egg – The eggs are inserted on end in the undersides of new leaves. The eggs are whitish to light beige with the apex tending to be slightly darker.
Nymph – The nymphal stage appear glassy to opaque yellowish and may or may not have dorsal spines, depending on leaf characteristics. The body is flattened and scale-like with the margin relatively near the leaf surface. There is not a marginal palisade of waxy spines.
Pupa – The pupa or fourth nymphal instar will be somewhat darker beigeish-yellow and opaque. Pupae are relatively more plump compared to previous nymphal stages. The apex of anterior and caudal spiracular furrows have a small amount of white wax deposits. The caudal setae are prominent, and the caudal end is somewhat acute. Dorsal spines are present when the host leaf is hairy and absent when the host leaf is smooth.
Distribution – Silverleaf whitefly occurs around the world in tropical and subtropical areas and in greenhouses in temperate areas. It has been reported from all southeastern states. Additionally, it has been reported from Arizona, California, District of Columbia, Maryland, and Texas.
Host Plants – The number of host plants is extensive; however, the plant families most often reported are Leguminosae, Compositae, Malvaceae, Solanaceae, Euphorbiaceae, Convolvulaceae, Cucurbitaceae, Labiatae, Verbenaceae, Cruciferae, Amaranthaceae, Rosaceae, and Moraceae. The most frequently reported hosts in the southeastern United States are poinsettia, gerbera daisy, and tomato.
Damage – Direct damage is caused by the removal of sap, and indirect damage as a disease vector. The silverleaf whitefly is a vector for several important virus diseases of lettuce and melons in the southwestern United States. Both the adult and nymphal stages contribute to direct damage. Chlorotic spots sometimes appear at the feeding sites on leaves, and heavy infestations cause leaf wilting. The excretion of honeydew and the subsequent development of sooty mold fungi also may reduce photosynthesis and other physiological functions of the plant. Even though the silverleaf whitefly is considered an economic pest, little information is known about the damage it causes or the economic thresholds.
Life History – Developmental times from egg deposition to adult emergence appears to be primarily controlled by temperature, humidity, and host plant. These times will vary from 16 to 38 days depending on these factors. The number of eggs laid by each female over her lifetime varies considerably, but appears to be around 80 to 100. There have been reports (in Israel) that repeated applications of insecticides have produced a highly fecund (300 eggs per female) strain of silverleaf whitefly. Apparently at temperatures above 36°C, eggs fail to hatch. "Crawlers" hatch from the eggs and crawl about until they insert thread-like mouthparts into the underside of the leaf to feed. They tuck their legs and antennae underneath and settle down closely to the leaf surface.
Crawlers molt into scale-like nymphs that also suck out sap. Nymphs molt a second and third time. The fourth stage eventually becomes a nonfeeding pupa. The adult whitefly develops within the pupa. Adults emerge from the pupa through a T-shaped slit about a month from the time the egg was laid. Females live about 2 weeks.
Control of silverleaf whiteflies is difficult because the eggs and older immature forms are resistant to many aerosol and insecticide sprays (in addition, the adults are extremely resistant to dry pesticide residue). For good control, the pesticide mixture must be directed to the lower leaf surface where all stages of the whiteflies naturally occur. One must make regular applications of pesticides to control crawlers and second stage nymphs until the last of a whole generation of immature whiteflies has hatched. However, some of the pyrethroid pesticides are somewhat more effective and need not be applied as often. Neem seed extract is not as acutely toxic as some of the synthetic pesticides, but has the advantage of being toxic to young nymphs, inhibiting growth and development of older nymphs, and reducing oviposition by adults. For specific chemical control recommendations, see Cooperative Extension publications on ornamental plant and vegetable pests.
Vegetable leafminer, Liriomyza sativae Blanchard, Agromyzidae, DIPTERA
Adult – This shiny black fly has variable yellow markings and is 1.0 to 1.8 mm long.
Egg – The white oval egg, about 0.2 mm long, sometimes is visible through the upper epidermis of the leaf.
Larva – The newly hatched larva is nearly colorless and only 0.1 mm long. The fully grown maggot, about 3.0 mm long, has a bright yellow, translucent body, and black mouthparts. Each maggot has a slightly pointed head and a more rounded abdomen.
Pupa – The flattened, segmented pupa is bright yellow at first but gradually turns brown. It is oblong-oval in shape and slightly less than 2 mm long.
Distribution – The vegetable leafminer is found from the tropics into the southeastern and southwestern United States. It occurs at least as far north as Tennessee and Ohio. Since this leafminer has been confused with closely related species for a long time, the extent of its distribution is not known precisely.
Host Plants – Closely related to the serpentine leafminer which feeds almost exclusively on crucifers, the vegetable leafminer infests a wide variety of plants. Some economically important weed and cultivated crop hosts include squash, okra, pea, tomato, bean, cabbage, turnip, potato, tobacco, cotton, radish, spinach, watermelon, beet, pepper, alfalfa, clover, vetch, and plantain.
Damage – Like serpentine leafminers, vegetable leafminers create lightly colored, irregularly winding mines in leaves. The mines are generally S-shaped and may be enlarged at one end. Infested leaves are favorable habitats for invading bacterial and fungal plant pathogens. Also, since heavily mined leaves may have nearly 100% of their mesophyll removed, photosynthetic efficiency is greatly reduced.
Severe infestations may cause the foliage to turn brown and appear burned. Damaging infestations are most likely to occur after crops have been treated weekly with insecticides such as methomyl or carbaryl. These pesticides kill parasitic wasps which normally keep the leafminer populations at acceptable levels.
Life History – Vegetable leafminers feed and breed year round in the southern areas of Florida and Texas. In North Carolina, they overwinter in soil as pupae. Generally, adult flies which emerge in April or May live only 4 to 10 days. After mating, females insert eggs into leaf tissue from the underside of the leaf. Three to 8 days later, eggs hatch and young larvae begin feeding, each one creating its own mine. Although the leafmining stage may last up to 12 days, it is usually completed in 4 or 5 days during summer. Larvae pupate for about 10 days (longer in spring and fall) at the enlarged ends of the mines or in the soil. A new generation is produced approximately every 23 days. At least 5 generations occur each year in southern states. The number is higher in the tropics and under greenhouse conditions.
Practical on a small scale, the removal of infested tomato leaves helps keep leafminer populations at a manageable level. Economically important leafminer damage rarely occurs on cucurbits. Butternut 23 and Cozella are the only squash varieties which show resistance. On vegetable crops other than cucurbits, however, the use of insecticides remains the most reliable method of control. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.
Western Flower Thrips
Western flower thrips, Frankliniella occidentalis (Pergande), Thripidae, THYSANOPTERA
Adult – Western flower thrips is about 1 mm long, with the female larger than the male. The female varies from yellow to dark brown, and has a more rounded abdomen. The male is always pale yellow and has a narrower abdomen.
Egg – Yellowish eggs cannot be seen because they are laid into the plant tissue.
Larva – The larva develop through two instars and are distinctly yellow. Second instars become whitish before molting.
Prepupa and Pupa – Both prepupa and pupa are yellowish, quiescent nonfeeding stages. The antennae and wing pads are typical for most thrips species.
Distribution – The distribution was thought to be limited to west of the Mississippi River before 1980. However, this thrips has become the most prevalent species attacking greenhouse flowers throughout the United States and Canada, and many countries in Europe and Asia.
Host Plants – This thrips feeds on almost any flowering plant. Carnations, chrysanthemums, gerberas, geraniums, marigolds, pansies, peppers, tomatoes, and roses are the major host plants.
Damage – The western flower thrips feeds on the flowers and foliage by inserting its modified left mandible into the tissue, and sucking the fluids from cells. Oviposition and feeding scars reduce the aesthetic quality and marketability of ornamental plants. When thrips feed on developing tissues, affected cells are unable to expand, and mature leaves and petals are distorted. When thrips feed on expanded tissue, affected cells become filled with air, which imparts a silvery appearance. This thrips also is an important vector of tomato spotted wilt virus and impatiens necrotic spot virus.
Life History – Females lay eggs in tender plant tissue. The eggs hatch in 2 to 14 days, depending on temperature. First-instar larvae begin feeding on egg eclosion. Second-instar larvae also feed on plant tissue, usually in flowers. These larvae are found in the protection of perianth of the flower or within developing terminal foliage. Late in the second instar they stop feeding and move down the plant to pupate. Thrips develop through two quiescent, nonfeeding pupal stages in the soil, plant litter, or in a protected area on the plant. Adults emerge and resume feeding on flowers, buds, and terminal foliage. The entire life cycle from oviposition to adult emergence can take 12 days in hot weather to 44 days in cool weather.
The thrips are difficult to manage with pesticides because of their thigmotactic behavior causes them to feed deep in the flowers and buds where they are sheltered from chemicals. Chemical management of western flower thrips has received much attention, but control remains difficult. Natural enemies have been investigated and biological control programs using insidious plant buts on predaceous mites in the genus Amblyseius have been used in greenhouses. Screening has been shown to effectively exclude western flower thrips. For insecticide rates, consult current Cooperative Extension publications on ornamental plant and vegetable pests for your state.
Publication date: Feb. 10, 2003
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