Greenhouse Whitefly
May 9, 2008
DESCRIPTION Adults: About 1.5 mm long, the adult is a white insect that resembles a tiny moth.
Eggs: The small oblong eggs, pale green to purple, are deposited on the lower leaf surface, often in a circle or a crescent.
Nymphs: The first instar nymph is mobile and similar to a scale insect crawler. Later nymphal stages are yellowish with red eyes, and are immobile. They resemble soft scale insects, but have an orifice on the back through which honeydew is expelled.
Pupae: The oval pupa is pale green to black when parasitized. The normal color, when empty, is clear-glassy with a fringe of glassysetae, and with some long glassy setae on the dorsal surface. The pupal case sits upon a vertical palisade of closely appressed wax rods (these are readily visible in side view).
BIOLOGY Distribution: Greenhouse whiteflies are worldwide pests of greenhouse-grown ornamentals and vegetables. First discovered in England in 1856, they 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. Even trees may be infested (redbud, Kentucky coffee berry, and avocado).
Damage: Infested plants become chlorotic and unthrifty. Honeydew and sooty mold further detract from the appearance of the crop. Unless controlled, greenhouse whiteflies may completely destroy the commercial value of floricultural crop.
Life Cycle: Greenhouse whiteflies reproduce relatively slowly (one generation every 30 to 45 days), but each may lay up to 400 eggs and live as long as 2 months. Adults are usually found on the lower surface of new leaves. The 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 nymphs and then into pupae. Finally, a new generation of whitish yellow adults emerges. They are soon covered by a white waxy bloom.
CONTROL Lower greenhouse temperatures used in the culture of some bedding and potted plant varieties tend to encourage infestations, because naturally occurring parasitic wasps (Encarsia formosa) are reproductively inhibited at temperatures below 24°C (75°F). The lady beetle Delphastus pusillus also attacks greenhouse whitefly.
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. However, some of the synthetic
pyrethroid and synthetic insect growth-regulator pesticides are extremely effective and need not be applied as often.
Hemispherical Scale
May 9, 2008
DESCRIPTION Adults: Depending on the host plant, the adult scale may vary in size. The scale varies from 4.5 millimeters on Cycas to as small as 2.0 millimeters on Asparagus fern. Relatively hemispherical, brown, smooth, and shiny, the scale may resemble a miniature army helmet. Young females may have a pattern of ridges in the form of the letter “H” on the dorsal surface.
Eggs: The oblong, pinkish beige eggs are about 0.7 millimeter long and are protected by the mother’s body in a mass of hundreds.
Crawlers: The flat, pinkish beige crawler is about 1.0 millimeter long with two red eye spots. The antennae and legs are short and spindly. There are two setae protruding from the rear.
Nymphs: Nymphs are semitransparent, light yellow or pink, and flat (young) to humped (older). They are so closely attached to the host plant that the legs and antennae are concealed. Two pale lines start at the margin on each side and fade in intensity toward the middle. Nymphs and young adults may exhibit the characteristic “H” pattern of the black scale group.
BIOLOGY Host Plants: The hemispherical scale insect has a wide range of hosts including bamboo, camellia, chrysanthemum, crape myrtle, croton, ferns, figs, gardenia, honeysuckle, lily, orchids, and zamia.
Damage: The secretion of honeydew and subsequent formation of sooty mold detracts from the beauty and commercial value of the plant. Feeding causes the plant to become stunted and lose its leaves.
Life Cycle: The hemispherical scale insect is a tropical insect that has become a common greenhouse pest. In warmer temperate areas, the scale can live outside. Unlike many other scales, the hemispherical scale secretes little wax. However, the scales do produce much honeydew which allows sooty mold to grow. Males are unknown and reproduction is by parthenogenesis. Each female may deposit up to 1000 eggs. After laying the eggs, the female dies and her body shrinks to form a cup or helmet over the eggs.
Development for the egg stage and the three nymphal instars requires at least 40 days and may take as long as 105 days. There may be several generations each year in the greenhouse, with all stages being present at any one time. The nymphs do not move much once they have begun to feed. The hemispherical scale insect has a low rate of parasitism indoors, and it often becomes a serious pest.
MANAGEMENT STRATEGIES Biological Control: The most important parasite of hemispherical scale in the United States is Metaphycus helvolus Compere.
Pesticides: Hemispherical scale insects are relatively difficult to control because the eggs and young nymphs are protected by the body of the mother.
Composite Thrips
May 9, 2008
DESCRIPTION Adults: Females of this species are yellowish brown to dark brown, and the head is small with black eyes and red ocelli. Intermediate antennal segment, apex of fore femora, and all tarsi lighter, becoming yellow brown to yellow. The forewings are brownish gray. Prothorax longer than wide and moderately covered with setae. Males are smaller and paler than females. Males have a dark brown head and pale yellow body.
Eggs: The eggs are yellowish and small, almost spherical (with a slightly narrow anterior end). Eggs average 0.12 mm long and 0.08 mm in diameter.
Larvae: The first instar is translucent to whitish yellow and is 0.36 to 0.68 mm long. The second instar is yellow with the head smaller in relation to thorax and abdomen. Body length is 0.68 to 1.0 mm.
Pupae and Prepupae: The prepupa is sluggish and moves only when disturbed. It is pinkish yellow and 0.71 to 1.0 mm long. It rests in the outer bracts of the flower or between the lower ends of florets. The pupa is inactive, robust, and pinkish yellow. Male pupae are 0.63 to 0.81 mm and female pupae are 0.89 to 1.4 mm long.
BIOLOGY Distribution: The composite thrips is a new world thrips found throughout most of North America. It is an occasional inhabitant of greenhouses throughout the southeastern United States.
Host Plants: Adults and larvae usually are found in the flowers and are rarely found on the foliage. Composite thrips occurs in great abundance on flowers of chrysanthemum, cosmos, zinnia, and marigold.
Damage: Heavy infestations cause damage to the corolla, stamens, and developing seed of plants in the Compositae. Petals lose pigmentation, senesce early, and drop prematurely.
Life Cycle: The life cycle requires 11 to 13 days at 27° C. Eggs hatch in 72 to 80 hours. The first and second instars last about 3 days each, the prepupal stage requires 24 hours or less, and the pupal stage varies from 24 to 48 hours. Eggs are laid inside the tissue of the disc floret. Females are 15 times more numerous than males. Reproduction is both sexual and parthenogenetic. New females begin to lay eggs 72 to 96 hours after emergence from the pupal stage.
Citrus Whitefly
May 9, 2008
DESCRIPTION Adults: The adult is a tiny, moth-like, four-winged, mealy-white insect with a wing span of less than 4.3 mm. Most often they rest on the undersides of leaves and fly about when plants are disturbed.
Eggs: The citrus whitefly lays yellow eggs with a nearly smooth surface. The eggs are about 0.25 mm long, elliptical, and most frequently laid on young tender leaves.
Nymphs: The first instar is the only mobile nymphal stage. After the first instar the nymphs are flattened, oval, and similar in appearance to soft scale insects. Nymphs are translucent, oval in outline, and very thin. The leaf color will show through the thin nymphal body, therefore nymphs are difficult to see.
Pupae: The pupal case is very similar to nymphs, but is slightly thickened and more opaque. The red eye spots of the adult are very prominent in developing pupal cases.
BIOLOGY Distribution: Reported from Virginia southward and around to Texas, then westward to California.
Host Plants: The primary host plant is citrus of all types, but many ornamentals are also hosts. The most common are Allamanda, banana shrub, Boston ivy, chinaberry, English ivy, gardenia, lilac, pear, osage orange, and privet.
Damage: Direct damage is caused by the removal of sap. Indirect damage is caused by the excretion of copious amounts of honeydew where sooty molds grow. This black mold will contribute to poor aesthetics and perhaps interfere with photosynthesis.
Life Cycle: Winter or colder periods are passed as late nymphal stages on the undersides of leaves. These may be on some remaining plants or weeds growing under benches. In the spring or when heat is applied adults will emerge and deposit eggs on the undersides of new plant growth. These eggs will hatch in 8 to 24 days, depending on the temperature. The nymphal stage will last from 23 to 30 days. Overall the life cycle from egg to adult will vary from 41 days to more than 300. The adult will live as long as 27 days.
CONTROL Controls are difficult because the eggs and nymphs are located on the underside of leaves, and they may also be resistant to some aerosol chemicals. Adult control usually will involve multiple applications as the nymphs mature and all have emerged as adults. Some of the new synthetic pyrethroids make controls much more successful. However, chemicals must be alternated to lessen the chance of a chemical-tolerant or resistant population developing. In some states biological control using Encarsia lahorensis has been very successful. This parasitoid should be functional in the Gulf Coast states and warmer areas of other states.
Melon or Cotton Aphid
May 9, 2008
DESCRIPTION Adults: This is a small aphid, smaller than most other aphids. The winged adults are about 1.25 millimeters long, soft bodied, and yellow to dark green with a black head and thorax. The wings are held rooflike over the abdomen at rest. Wingless adults tend to be 1.0
to 1.5 millimeters long, uniform in color, and yellow to dark green. The antennae and cornicles are shorter than those of winged adults. Cornicles are small, tail-pipe-like structures on the end of the body. Pale individuals tend to be smaller and to have fewer antennal segments than dark individuals.
Nymphs: Nymphs resemble adult aphids except for size (about 0.5 to 1.0 millimeter long). Those destined to be winged adults have wing buds in the later instars.
BIOLOGY Host Plants: Melons and other cucurbits, okra, hops, strawberries, beans, spinach, tomatoes, clover, asparagus, citrus, catalpa, violet, hydrangea, begonia, ground ivy, and weeds are some melon aphid hosts. They have been discovered feeding on plants in 25 plant families. The melon aphid is an important pest of cotton and is also called the cotton aphid.
Damage: The melon aphid feeds by piercing the plant surface with its threadlike mouthparts to suck out plant juices. This feeding causes distorted growth, decreased yield, reduced quality of yield, and prematurely ripened fruit. The fruit may be covered by the feeding aphids’ honeydew and by cast skins. The melon aphid transmits several important plant viruses including cucumber mosaic, onion yellow dwarf, citrus quick decline, lily symptomless diseases, and lily rosette.
Life Cycle: The melon aphid is an important pest of both agricultural and ornamental plants. Being practically omnipresent, it feeds upon many host plants. The melon aphid spends the winter on weed hosts and on cold-tolerant plants probably both as nymphs and adult females in the south. During warm periods of winter they start feeding until cold weather inactivates them again. In the spring the adult females move to new hosts and start feeding and rapidly reproducing. In northern climates the aphid overwinters in the egg stage. Indoors and in greenhouses the aphids feed and reproduce throughout the winter. Melon aphids commonly start out on one plant and spread out from that point. On woody ornamentals such as gardenias, feeding is confined to new growth in the spring.
For the melon aphid there are two kinds of hosts, primary and secondary. In late fall, aphids feed upon primary plants mate and lay overwintering eggs. Melon aphids feeding on secondary plants always give birth to live young. In spring, winged forms usually infest new plants, both primary and secondary, and the females produce live nymphs. Within about a week the new nymphs mature into wingless females that begin to bear young of their own. As the plant becomes crowded, more and more of the offspring develop into winged females which in turn migrate to other plants to begin new infestations. Wingless forms usually predominate in low aphid populations.
MANAGEMENT STRATEGIES Biological Control: Natural enemies may control minor infestations on outdoor ornamentals. Syrphid fly maggots and ladybird beetles and their larvae feed upon melon aphids. Braconid wasps parasitize the aphids, and ants feed on the honeydew excreted by feeding aphids.
Pesticides: Because the winged forms are 2 to 3.7 times more resistant to organophosphate pesticides than are wingless forms, infested plants in the greenhouse should be sprayed thoroughly when aphids are first noticed.
Click HERE or HERE for information on controlling Aphids
Chrysanthemum Aphid
May 9, 2008
DESCRIPTION: Adults: The winged adults are about 2 to 2.5 millimeters long; soft bodied; and dark, shining mahogany brown. Due to their dark color they were once called “blackflies.” Wingless adults are only 1.5 millimeters long. Small, black, sturdy cornicles are found on the end of the body.
Nymphs: Nymphs resemble smaller versions of the adult aphids (0.6 to 1 millimeters). Nymphs have a dull, brick-red bodies with relatively long legs and antennae. The cornicles are short and dark. The outer two-thirds of the legs and antennae are gray (young nymphs) to dark gray. Older nymphs have proportionally longer cornicles. Those destined to be winged adults have wing buds in the later instars.
BIOLOGY Host Plants: Chrysanthemum is the only known host for this aphid in North America, but it has been reported on a few related plants in Asia.
Damage: The chrysanthemum aphid feeds by piercing the plant surface with its threadlike mouthparts to suck out plant juices. They gather about the terminal buds and feed on the new growth. This feeding causes distorted growth and the leaves may be covered by the feeding aphids’ honeydew and cast skins. Sooty mold may grow on the honeydew giving the leaves and stems a black appearance. Chrysanthemum aphids are able to transmit chrysanthemum vein mottle virus and chrysanthemum virus B.
Life Cycle: Only female chrysanthemum aphids are known. They reproduce by giving live birth to more females, without mating. Chrysanthemum aphids overwinter in greenhouses where they feed throughout the winter. During the warmer months they leave the greenhouses in search of new plants. They also may be moved about as plants are shipped or sold. When the winged female stage infests new plants, it usually starts feeding and producing live nymphs. Each female can produce four to eight young aphids per day.
Within about a week the new nymphs mature into wingless females which begin to bear young of their own. One aphid on a plant in a short time may build the population up to hundreds of individuals . As the plant becomes crowded, more and more of the offspring develop into winged females which in turn migrate to other plants to begin new infestations.
MANAGEMENT STRATEGIES Infested plants in the greenhouse should be sprayed thoroughly when aphids are first noticed. On outdoor plantings, natural enemies may control minor infestations.
Melon Thrip
May 9, 2008
DESCRIPTION Adults: Melon thrips have a clear yellow body without darker blotches but with thick, blackish body setae. Antennal colors variable. The pronotum has two pairs of major setae and posterior angles and antennal segments 3 and 4 each have a forked sense cone.
Eggs: No description available.
Larvae: No description available.
Pupae and prepupae: No description available.BIOLOGY Distribution: The melon thrips was first established in the United States in Hawaii around 1982. An established field population was first discovered in the continental United States in 1991 in Florida. It has been distributed in South and Southeast Asia, Pacific Islands, and Caribbean Islands.
Host Plants: The melon thrips has an extremely wide range of host plants, including nearly all kinds of vegetables, many fruit trees and weeds, and several flowering plants such as chrysanthemums and carnations. They quickly build up heavy infestations causing severe injuries.
Damage: Immature thrips and adults feed on leaves, (first along midribs and veins), stems (near growing tip), flowers (all parts), and fruits (on the surface). Severe damage results from sucking plant sap leaving silvery scars from empty cells. Heavy feeding results in a silvered or bronzed appearance and will kill the plant.
Life Cycle: The melon thrips eggs are deposited within plant tissues singly. Larvae have two stages, that feed on plant tissues. The second instar larvae, when mature, fall to ground, where they molt to prepupae and pupae in the soil. After emergence, the adults move to the growing parts of the plants such as young leaves, flowers, or young fruits, where they feed and lay eggs. Adults are usually found on young leaves, while larvae are found on lower or older leaves. Few thrips are found on flowers or fruits. At higher temperatures generation times are shorter. The average development times are: 80.2 days at 15° C, 40.7 days at 20° C, 24.8 days at 25° C, and 20.5 days at 30° C. The reproductive rate reaches maximum at 25° C. The adults reproduce sexually and parthenogenically.
CONTROL: Chemical insecticides have not been consistent in controlling this pest. None cause more than 80 percent mortality. Several predators attack the melon thrips, including predaceous mites in the genera Amblyseius and Phytoseiulus (Acari: Phytoseiidae), insidious flower bugs, and several species of predaceous thrips, ants, and rove beetles.
Mexican mealybug
May 9, 2008
DESCRIPTION Adults: The female Mexican mealybug adult is 3 to 4 millimeters long, oval, grayish and covered with a thin waxy secretion. There are three parallel rows of small waxy tufts down the back. This insect is a short-tailed mealybug (the caudal filaments do not exceed 1/4 the body length). The lateral filaments are also short. Males are small gnat-like insects with only two wings. Adult Mexican mealybug males have four waxy, posterior filaments.
Eggs: The egg sac is white, dense, narrow, and longer than the female secreting it.
Nymphs: The nymphs are small and yellowish with white waxy secretions.BIOLOGY Host Plants: The Mexican mealybug is found commonly on numerous ornamental plants, a few of which are aralia, chrysanthemum, English ivy, geranium, Gynura, hollyhock, Ixia, lantana, and poinsettia. This insect is also a minor pest of lima beans in the warmer parts of the United States.
Damage: Wilting and stunting are common symptoms of Mexican mealybug attack. This insect can be as damaging as the citrus mealybug. The mealybugs and ovisacs also disfigure heavily infested plants.
Life Cycle: In the greenhouse, the Mexican mealybug may have seven complete generations in one year. The average time required from oviposition to the adult stage is 47 days. Each female deposits about 400 eggs. The eggs are enclosed in an elongate cottony mass called the ovisac that originates at the back of the female. The ovisac is about 6 millimeters long. The eggs hatch in 6 to 14 days. The life cycles of the male and female Mexican mealybugs differ. A female passes through three nymphal stages only. Male Mexican mealybugs pass through two nymphal stages and two resting stages (prepupal and pupal stages). Normally, these mealybugs are found above ground on the leaves, stems or flowers, but occasionally will be found feeding on the roots.
MANAGEMENT STRATEGIES Pesticides: For chemical control recommendations, consult the Cooperative Extension Service.
Ground Beetle
May 9, 2008
Ground beetles make up one of the largest groups of beetles in North America, with more than 2200 species. Although there is some variation in their body shape and coloring, most are shiny and black (some are metallic), and have ridged wing covers. Another characteristic common to ground beetles is a smaller head than thorax, and threadlike antennae.
They may be confused with cockroaches such as the oriental roach (both are shiny and very dark) but beetles have hardened front wings where roaches either have leathery wings or no wings.
Adults are active at night and tend to hide under rocks during the day. They will run when exposed. They come out at night to feed o unsuspecting insects. Likely targets include caterpillars, root maggots, snails, and other soft bodied insects. The fiery searcher, a very brilliantly colored ground beetle, was imported to assist in the control of gypsy moth larvae Most species do not use their wings, but a few may fly to lights at night. One group of ground beetles, called bombadier beetles, have an interesting defensive mechanism.
When threatened, they raise the end of their body and fire a chemical gas with popping sound and smokelike puffs. The gas is irritating to enemies such as toads and would-be collectors. Ground beetle larvae, like adults, are important predators. The larvae live below ground, where they use their large pincher-like mandibles to devour soil-dwelling insects.
Adults may wander into homes by crawling through small openings or under doors. They will not stay inside-they prefer the outdoors. Since ground beetles are beneficial insects, control is not warranted. However, if they are creating a nuisance, move or remove hiding places next to the house such as log piles, mulch, and debris around the perimeter. Caulking and weatherstripping will close some entrance points. Beetles found indoors may be swept up and discarded.
If beetles are creating a nuisance by flying to lights at night, repositioning the lighting or changing white lights to yellow may reduce the attraction.
Onion Thrips
May 9, 2008
DESCRIPTION Adults: Adult females of onion thrips are about 1.1 to 1.2 mm long, yellow, with
brownish blotches on the thorax and the median portion of abdomen. Antennae are gray with the first
segment lighter than other segments. Males are rare.
Eggs: The eggs are very small, about 0.2 mm long, kidney shaped, and white. They are deposited
within plant tissues.
Larvae: The first instar larva is white, about 0.35 to 0.38 mm long. The second instar larva is
yellowish, about 0.7 to 0.9 mm long.
Pupae and Prepupae: The pupa and prepupa are similar to the second instar larvae in color and shape,
except for having small wing pads.
BIOLOGY Distribution: Onion thrips have been found in most countries throughout the world.
Host Plants: Onion thrips are extremely polyphagous. They inhabit leaves, shoots, and flowers of many
plants. It prefers to feed on onions, but feeds on many field crops, vegetables, various flowers,
and bedding plants. It may cause heavy damage to chrysanthemums and carnations.
Damage: Generally feeding of onion thrips cause yellowing or dropping of leaves, buds, or flowers.
High infestation results in stunted growth, brown blisters, white blotches, silvery whitish areas or
feeding scars. Young terminal leaves frequently show malformation when heavily attacked, with crinkly
surfaces, sunken and raised thin areas, marginal erosion, margin curling inwardly, and a chlorotic
yellowish appearance with grayish color along all large veins. Young buds may be killed as soon as they
come out. In addition, they freely feed within flowers, attacking the tender portions.
Life Cycle: Onion thrips have six to ten generations depending on temperature. Adults and larvae
overwinter in the soil or plant litter on the ground. Pupae and prepupae overwinter in the soil. The
average length of development is: 6 to 8 days for eggs, 10 to 14 days for larvae, 5 to 9 days for prepupae
and pupae, and about 20 days for a generation. It may take as long as 35 days for a generation if temperature
is at 15° C. The lower developmental threshold is about 11.5° C and using this threshold as a base,
development required 191 degree days. Adults reproduce parthenogenically through out the season, rarely
reproduce sexually, and resulting m that most adults in the field are female. The average adult life is
around 32 days, and pre-oviposition, oviposition and post-oviposition periods are 6.1, 22.5, and 3.9 days,
respectively. The average number of eggs laid by an unmated female is 37.4 (20 to 200).
CONTROL: The application of chemical insecticides is the common control measure.
The onion thrips problem in an integrated pest management program can be solved by using
selective pesticides or by using selective treatments such as soil drenches. A combination
of selective chemical insecticides and a predaceous mite in the genus Amblyseius (
Acari: Phytoseiidae) have been successfully used to control this thrips.
Login to your account
Hydroponics Tools
Related Links
Glossary of Terms
Shopping
FAQ
Contact Us
Write a Column!
Photo Gallery
Videos
Articles
del.icio.us
Digg
reddit
StumbleUpon
Green Lacewings
Mexican Mealybug
