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Chapter 9: insects and other plant pests.

KEY TERMS

contact pesticide degree day gradual honeydew host plant instar metamorphosis molt nonselective pesticide pheromone trap selective pesticide systemic pesticide vector

The interaction between insects and plants can be positive or negative. Insects such as butterflies, moths, bees, and even ants pollinate plants and obtain nectar and pollen as food rewards. But some insects use the plants as food, usually to the detriment of the plants. In the same way that pollinators evolved to serve plants, some insects have evolved to feed off them. In other words, certain plants, sometimes referred to as host plants, attract specific pests. A good example of this is the butterfly milkweed plant and the monarch butterfly. The monarch butterfly is attracted to the butterfly milkweed plant, whose leaves contain a certain chemical compound that is toxic to birds but not to monarchs. Monarch larvae (caterpillars) accumulate this toxin while feeding off the plant, which then makes them toxic to would-be predator birds. Birds have come to recognize monarchs and, finding them distasteful, leave them alone. The milkweed plant is not so lucky, however, as a few monarch larvae can defoliate the plant in a short period of time. Table 9-1 shows major insect pests and the damage they cause.

COMMON PESTS

In part because of the huge number of cultivated species, there are many pests of horticultural plants. Although some are specific to certain species or related species of plants, others are common to a wide variety of plants. Of the latter, aphid, scale, mite, beetles, and larvae of butterflies and moths (caterpillars) are common on a wide range of plant species. Common pests of greenhouse and indoor plants include aphids, whiteflies, mites, fungus gnats, mealy bugs, and shore flies (Fig. 9-1). Individual plants have pests that affect them specifically, and these should be researched and understood before undertaking cultivation of a specific plant or crop.

Insect Families and Related Species

Insects and their relatives are arthropods. This means they have segmented bodies and an exoskeleton and respire by gills or tubes called trachae. Arthropods include insects, spiders, mites and ticks, centipedes, and millipedes. Insects are distinguished from other arthropods in that they have three body segments, usually six legs, and a pair of antennae (Fig. 9-2). There are other characteristics that distinguish different types of insects including their mouthparts, wing structure, and the type of metamorphosis they undergo in their life cycle. Insects generally have one or two pairs of wings, although these may be absent. Mites belong to the Arachnida, having two body segments and eight legs (Fig. 9-3). They lack antennae. The major arthropod orders in which plant-damaging pests are found include the following: Arachnida (spiders and mites), Coleoptera (beetles), Diptera (flies), Hemiptera/ Homoptera (true bugs), Lepidoptera (butterflies and moths), Orthoptera (grasshoppers and locusts), and Thysanoptera (thrips).

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Insects may be identified by direct observation, by their frass, or droppings, and by the crop they are found on and the damage they do there. Some insects, such as aphids and whiteflies, feed on plant juices and excrete a sticky, sugary substance called honeydew, which attracts ants. Honeydew is also a good substrate for molds and fungi, and often black sooty mold is observed when such pests have invaded a plant.

It may be possible to identify a pest problem, even when the pest is not directly observed. Feeding damage often indicates the mouthparts of the offending insect. Some have chewing mouthparts, others have piercing-sucking mouthparts, and yet others have rasping, saw-like mouthparts. The resultant damage may appear as ragged holes in leaves, small, pin-prick-sized necrotic tissue, or ragged edges of a leaf (Figs. 9-4 through 9-15, see pages 154-157). Insects with chewing mouthparts include beetles, grasshoppers, grubs, and caterpillars. Those with piercing-sucking mouthparts include aphids, scales, whiteflies, and leafhoppers. Mites also pierce and suck. Thrips have rasping-sucking mouthparts.

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Insects can harm plants in a number of ways, with feeding being the most obvious. In addition, they also act as vectors for viruses or disease pathogens, they bore holes into plants to lay eggs inside them, and they exude honeydew to support fungal growth (Fig. 9-16). Nematodes are microscopic worms that may live in the soil or inside plants, depending on the species. The population of those that reside in soil can build up if susceptible plants are grown repeatedly in the same location. Crop rotation can help reduce nematode populations in the soil. Some species of nematodes are beneficial, as they eat plant pests and sometimes pathogens (Fig. 9-17).

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INSECT LIFE CYCLES

If you want to control pests on plants, it is good to understand the life cycle of the pest with which you are dealing. It is especially helpful to learn when they appear during the season, if they lay eggs, where they lay their eggs, and what stage of their life cycle causes the damage to plants. Furthermore, many insects experience more rapid development as the temperature warms up in the spring. Their emergence is determined by degree days (see chapter 7 for a discussion on degree days), not calendar days. Thus, the warmer the spring is, the sooner insect pests will emerge. The same is true in the greenhouse environment, in that the warmer it is, the faster insects will go through a life cycle, and, if a chemical control strategy is used, the more often chemical controls will be required.

Metamorphosis

Many species of insects undergo metamorphosis from egg to larvae to adult. In addition to these phases, some insects experience a pupal stage in which they undergo drastic changes in morphology, often from a crawling to a winged body (Fig. 9-18). Insect pests of plants may undergo either complete or gradual metamorphosis. There are two other types of insect metamorphosis, none and incomplete, but most insects in these groups are not plant pests.

COMPLETE METAMORPHOSIS. Complete metamorphosis has four stages: egg, larva, pupa, and adult. Butterflies and moths undergo complete metamorphosis. The larval form is called a caterpillar. This is the most damaging stage of the butterfly and moth life cycle. Larvae consume vast amounts of vegetation before pupation. Adults generally feed on nectar and are usually short-lived. The cycle is complete when the adults lay eggs. Other insects with complete metamorphosis, such as the Colorado potato beetle have larvae and adults that both damage plants.

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GRADUAL METAMORPHOSIS. Gradual metamorphosis has three stages: egg, nymph, and adult. Some species have several nymphal stages in which the body form is similar but becomes larger in each stage until finally the adult form emerges. Grasshoppers undergo gradual metamorphosis. Nymphs do not have wings, as adults do, but both stages eat vegetation and are therefore the most damaging stages of the life cycle. Egg-laying again completes the life cycle.

As nymphs and larvae grow, they may have to molt, or shed their skin. Molting involves the loss of the old exoskeleton followed by a period of vulnerability in which the new skin is soft and pliable. The stage between molts is called an instar. The number of molts and instars varies by species.

PEST CONTROL METHODS

Manual

When infestations are noticed early, it may be possible to eradicate them manually. This involves removing the offending pest by hand. This only works if there is lots of low-cost labor or very small acreage, as in the home garden. Favorable environmental conditions allow rapid life cycles and result in an exponential increase in insect pests. Often a pest such as tomato hornworm is not present in large quantities, so simply removing them as they appear is enough to maintain total control. Manual methods may be used in conjunction with other controls, depending on how many plants are infected and the convenience and efficiency of manual removal.

Cultural

Cultural control methods rely on strict adherence to sanitary garden management and keen observation. Insects use scents called pheromones for communication and mate attraction. These may be synthesized and used to trap insects in special pheromone traps.

Many insects are attracted to the color yellow, so this attraction is exploited in the use of yellow sticky cards in greenhouses. Because thrips are more attracted to the color blue, blue sticky cards are used to attract them. Pheromone traps and sticky cards can be used to trap pests or to monitor their presence.

TRAP CROP. Trap crops are planted near the desired plant to attract pests to them, thus saving the desired food plant from invasion. It is even acceptable in organic gardening practices to then spray a pesticide on the trap crop to control the insect species, while maintaining a pesticide-free food crop.

MONITORING. Monitoring insect pests for threshold levels is an important component of integrated pest management (IPM). This tool can help in the decision as to when to apply pesticides and which pesticide to use. Threshold levels are based on aesthetic and economic considerations. For the cut flower and potted flowering plant market segments, little to no damage can be tolerated, whereas for other crops, some low level of damage may not harm the overall value of the crop. Economic considerations include the cost of applying pesticide balanced against the increased price that may be obtained by having a cleaner crop. As long as this is a negative value (i.e., the cost to apply is greater than the costs recuperated in sales), it is not feasible to apply pesticide. Costs of applying pesticides include the actual cost of the pesticide plus the time required for applying, use of equipment, and other incidental costs.

BARRIERS. Some greenhouses install physical barriers to pests and diseases. For example, ventilators may be covered with screening fabric to keep out small-sized insects. Double-door entryways may reduce the introduction of pests through doorways, and foot baths containing a disinfectant solution and placed at the entryway can reduce spread of disease pathogens carried on shoes.

Another type of barrier that can be readily applied in the garden is the use of row cover fabric to prevent pests from getting to the plants. Often this is necessary only for a window of time when the adult pests emerge and are looking for a place to feed. If they cannot access your plants, they will move on and not return. Understanding degree days can aid in monitoring for adult pest emergence and allow for effective preventive measures. Other barriers include collars placed around the base of individual plants or trees to prevent crawling pests from reaching the top of the plant. Tree wraps can protect fruit trees from rabbit and vole damage.

COMPANION PLANTS. Gardeners can benefit from the use of companion plants. This topic includes a lot of folklore, and scientists are just beginning to explore some of the claims. It is now known that some cultivars of marigolds exude a substance called thiopene through their roots that repels nematodes. Tomatoes are well-known for attracting root-knot nematodes. The nematode population builds up if tomatoes are grown in the same location in successive years. Marigolds can be used in rotation with tomatoes to effectively reduce root-knot nematode populations in the soil. There are many examples of companion plantings, but not all of them have been scientifically studied. There are probably sound reasons for the practice of companion planting, as this is a practice that has been used for a very long time.

CROP ROTATION. It is important to understand pest life cycles and whether they overwinter in the soil. In the case of those that do, crop rotation can provide a method of avoiding infestation in successive years. Because it also works for disease pests, crop rotation is always recommended. As a general rule of thumb, crops should be rotated with those from other families (i.e., do not follow a solanaceous crop such as eggplants or tomatoes with another solanaceous crop such as potatoes). Also, root, leaf, and fruiting crops should be rotated with each other.

Genetics

Traditional breeding techniques have produced some crops with insect resistance, although these are not available on the same scale as those bred with resistance to various diseases. Plant breeders look for plants that produce chemicals toxic to insects or those that have traits that make them undesirable to insects, such as thick cuticles or dense trichomes. Other plants withstand or outgrow the damage caused by insects and may have qualities that can be bred into improved cultivars. Molecular genetic procedures are used to develop insect-resistant plants while bypassing the lengthy process of traditional breeding. One common gene that is introduced using this technique is Bt from the bacterium Bacillus thuringiensis, which allows the plant to produce its own insecticide. These crops will be resistant to certain lepidopterous insects.

When purchasing seeds or plants, seek out resistant and tolerant cultivars and avoid susceptible ones. As each crop species has a particular pest complex, familiarize yourself with these problems before selecting what you will grow. Also, certain pests are more of a problem in certain geographical areas, so consult your local extension service personnel for guidance and information.

Chemical

Pesticides are available in a large variety of chemical and nonchemical formulations. In general, they may be either selective or nonselective in their activity on insects. Selective pesticides are very specific in which pests they control. Nonselective pesticides have a wider range and may kill all insects or a large group of related species. If you want to maintain beneficial insects, such as lady beetles and green lacewings, use selective pesticides.

Some pesticides may work only when they contact the insect directly; otherwise the pest will not be affected. These are called contact pesticides. Systemic pesticides are applied to the plant and translocated throughout it. When insect pests feed on the plant, they ingest the toxin and are killed.

Chemical controls fall into several major categories, based on their mode of action or their chemical class. Organophosphates, carbamates, insect growth regulators (juvenile growth hormones), and ovicides are some examples of insecticides. Conventional synthetic insecticides include chemicals such as diazinon, carbaryl, malathion, and methoxychlor.

Juvenile growth hormones target a specific pest at a specific point in its life cycle, causing its development to cease and not allowing it to metamorphose into its adult stage. Ovicides are effective on eggs. This is important, because many insecticides do not penetrate or affect the eggs and thus do not offer complete control of a pest. Other insect controls (biological, beneficial insects, natural derivatives, and horticultural soaps and oils) are discussed in the sections that follow.

Biological

The use of Bacillus thurengensis, or Bt, as it is commonly called, has made a major contribution to pest control in the United States in the past 20 or so years. It is a species of bacteria that kills lepidopterous insect larvae (caterpillars) when they ingest it. Bt is available in powders or can be mixed in a solution and sprayed on. It is not toxic to humans or animals. In fact, it is considered so safe that it is one of the controls approved for organic farming practices.

Beneficial Insects

Predator insects work in several different ways. They may simply feed on the insect pest, or they may parasitize it. Parasitizing wasps and tachinid flies lay their eggs in a host insect, such as a caterpillar (Figs. 9-19 and 9-20). When the eggs hatch, the larvae feed on the host insect and kill it, after which the larvae emerge and complete their development. Green lacewing larvae (Fig. 9-21), lady beetles (Fig. 9-22), praying mantises (nymphs and adults), ambush bugs, and spiders are carnivorous and will feed on insect pests (see Fig. 9-17). Predator insects exist in the environment, and their existence should be encouraged by limiting the uses of nonselective pesticides. In addition to their natural occurrence, predator insects can be purchased, and their use will be more successful if certain guidelines are followed.

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Natural Derivatives

There are naturally occurring chemicals that have pesticidal properties. These chemicals are often considered to be less toxic to the environment, although they may be more toxic than some synthetic chemicals. Nicotine is commonly used as a greenhouse fumigant. Pyrethrum is a toxic chemical produced by the flowering perennial, Chrysanthemum coccineum (Fig. 9-23). Synthetic compounds that resemble pyrethrum are called pyrethrins.

Azadirachtin is derived from the neem tree and has been found to have pesticidal activity. It is sold under a variety of trade names such as Azatrol, Align, Azatin, and Turplex.

Horticultural soaps and oils are effective against some pests and are a method of low to no toxicity or danger. Most insecticidal soaps contain salts of potassium or sodium, which dry the cuticle of soft insects such as whiteflies and aphids. Horticultural oils may be used to control aphids, lacebugs, spider mites, thrips, and whiteflies. The oil suffocates both adults and eggs and thus effectively reduces insect populations. Horticultural oil should not be applied when temperatures exceed 90[degrees]F or when plants are stressed or in bloom.

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Alien Pest Species

Some insects have become serious pests because they were introduced into an area where they lack natural predators. Some examples include gypsy moth, potato beetle, and emerald ash borer. Host plants also have not had time to evolve natural defense mechanisms against such exotic pests. Despite efforts by the Animal and Plant Health Inspection Service (see box) to prevent entry of potentially damaging pests into this country, they are still able to enter on clothing, airplane wheel wells, furniture, and so on.

IPM

IPM continues to develop as its use becomes widespread throughout the practice of agriculture and horticulture. Components of IPM in pest control include some of the areas discussed in other sections of this chapter: using genetic controls, using beneficial insects, using chemicals with lower toxicity, monitoring pest emergence and population size, and targeting susceptible stages of the pest life cycle. The USDA Agricultural Research Service (ARS) conducts extensive research on IPM programs for economically important crops.

ANIMAL AND BIRD PESTS

Animals and birds often cause greater problems than diseases or insects (Fig. 9-24). Deer eat many different fruits, vegetables, and landscape plants. In some areas they are not easily frightened by the presence of humans. As suburban areas grow into traditionally rural areas, this problem is expected to increase. For some people, the only solution is to abandon gardening altogether or to construct wire cages and fencing around everything. Some deer-resistant flowers and woody perennials are listed in chapters 16 and 17.

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SUMMARY

Plant pests can be specific to certain plants, or they may generalize and feed on a large number of plant species. In addition to the damage they cause by their feeding, they may also transmit plant pathogens. Insects usually have three pairs of legs whereas spiders and mites have four pairs. Their droppings are known as frass, which can sometimes aid in identifying them. Honeydew is another type of insect excrement. Insects have complete or gradual life cycles. Their development from egg to larva to adult is strongly affected by temperature. Degree days have been calculated to measure this response in some insect pests. Insect pests may be controlled in numerous ways, including multiple techniques referred to as integrated pest management.

HANDS-ON ACTIVITIES

* Study one crop and a major pest of that crop. Research the pest's life cycle and conditions for its successful survival. Identify IPM techniques used to monitor and control this pest. What other plants does this insect feed on? Where does this pest lay its eggs?

* Interview a farmer or nursery or greenhouse grower in your area. Ask him or her about major pest problems and strategies used to control them. Write a report about your findings.

* Interview a long-time local grower about pest control strategies they use today compared with what they would have done 20 or 30 years ago. How has the challenge of pest control changed, based on their experience? What kind of changes do they see for the future of pest management?

REVIEW QUESTIONS

1. What three body features distinguish insects from other arthropods?

2. Insect droppings are called--.

3. How many general stages are there in complete metamorphosis? Name them.

4. How many general stages are there in gradual metamorphosis? Name them.

5. What is molting?

6. What is an instar?

7. Compare and contrast selective and nonselective pesticides.

8. How does a systemic pesticide work?

9. What are pheromones? How does a pheromone trap work?

10. Discuss how parasitic wasps can control insect pests.

SELECTED REFERENCES

Lindquist, R. K. (1998). Identification of insects and related pests of horticultural plants. Columbus, OH: O.F.A. Services.

Nixon, P. L., Anderson C. D., Pataky N. R., Wolf, R. E., Ferree, R. J., & Bode, L. E. (1995). Illinois pesticide applicator training manual. Champaign, IL: University of Illinois at Urbana-Champaign.

Orton, D., & Green, T. Coincide. Carol Stream, IL: Labor of Love Conservancy.

APHIS: The Animal and Plant Health Inspection Service

APHIS "is responsible for protecting and promoting U.S. agricultural health, administering the Animal Welfare Act, and carrying out wildlife damage management activities."

Their mission was developed by the U.S. Department of Agriculture (USDA) in its efforts to ensure safe and affordable food. If such protection was not available, threats to America's food supply would be enormous. Some examples of APHIS protection involve the Mediterranean fruit fly and the Asian longhorned beetle. Both of these are major agricultural pests. If their entry into the country was not monitored, several billions of dollars in production and marketing losses would occur annually.

APHIS does its work by inspecting produce and livestock entering the country at our borders. They may quarantine products known to be vulnerable to a pest to determine whether the pest is indeed present.

Dr. Marietta Loehrlein currently teaches horticulture classes at Western Illinois University in Macomb, Illinois. She earned both her bachelor's degree in Agronomy and her master's degree in Plant Genetics at The University of Arizona. Her master's research project was concerned with germination problems associated with triploid seeds, from which seedless watermelons grow. Following that she worked for 5 years in a breeding and research program for Sunworld, International near Bakersfield, California. She worked with peaches, nectarines, plums, apricots, and cherries. Then she returned to school to earn her Ph.D. in Horticultural Genetics at The Pennsylvania State University. Her Ph.D. research focused on flowering processes in regal pelargonium (also called Martha Washington geraniums). While at The Pennsylvania State University, she bred a new cultivar of regal pelargonium, "Camelot." At Western Illinois University, Dr. Loehrlein teaches nine courses: Greenhouse and Nursery Management, Introductory Horticulture, Landscape Design, Landscape Management, Home Horticulture, Plant Propagation, Turf Management, and two courses in Plant Identification.
TABLE 9-1

Major Pests of Plants

                 DAMAGING                DESCRIPTION AND
PEST             STAGE(S)                DAMAGE

                 Arachnida (spiders and mites)

Mites            Adult                   Small, spider-like, having
                                           eight legs. Pierce and
                                           suck plant juices,
                                           creating pinprick holes.
                                           May construct
                                           webbing on plant.
                                           Some cause gall
                                           formation.

              Coleoptera (beetles, larvae worm-like or grub)

Bean leaf        Larvae                  Adult is yellow to red with
  beetle                                   four black spots on
                                           back.

Colorado         Adults and              Yellow- and black-striped
  potato           larvae                  beetle. Larvae are red
  beetle                                   with black legs and
                                           head and have two
                                           rows of black spots.

Cucumber         Adults and              Larvae is Southern corn
  beetle           larvae                  rootworm. Adult is
  (spotted                                 yellow beetle with
  and                                      black spots or yellow
  striped)                                 with black stripes.

Japanese         Larvae, adults          Adult is metallic green;
  beetle                                   larva is a white grub.

Various beetle   Larvae                  White or brownish white
  grubs                                    C-shaped larvae.
                                           Adults vary by species.

                            Diptera (fly)

Apple maggot     Larvae                  Adult is a small, dark
  fly              (maggots)               brown fly. Larvae are
                                           white, tapered
                                           maggots

Fungus gnat      Larvae                  Small black winged adult.
                                           Larvae are translucent
                                           white with shiny black
                                           heads.

Leafminers       Larvae feeds,           Adult is a winged fly
                   adult                   whereas larvae
                   punctures by            resemble caterpillars.
                   laying eggs             Larvae create
                                           serpentine tunnels in
                                           inner layer of leaf cells
                                           where they pupate.

                       Hemiptera/Homoptera (true bugs)

Aphids           Adult                   Pear-shaped, variously
                                           colored. Give live birth.
                                           Pierces and sucks plant
                                           juices, excretes
                                           honeydew.

Chinch bug       Larvae (nymphs)         Black body with white
                   and adults              wings. Wing length
                                           varies by species.
                                           Larvae may be red or
                                           black, depending on
                                           stage. Eggs are white
                                           with a red dot.

Leaf hoppers     Nymphs                  Colors and sizes vary by
                                           species. Nymphs suck
                                           phloem and excrete
                                           honeydew.

Mealybug         Nymphs suck             Nymphs suck phloem and
                   phloem,                 excrete honeydew.
                   excrete
                   honeydew

Scales (soft     Adults                  Females wingless, covered
  and                                      with waxy or hard
  armored)                                 covering. Round or
                                           oval shaped.

Tarnished        Adults and older        Brown bug with yellow,
  plant bug        nymphs                  black, and white
                                           markings. Nymphs
                                           resemble adults but
                                           lack wings; they have
                                           wing buds instead.

Whiteflies       Adult pierces           Pinprick holes in leaves,
                   and sucks               honeydew excretion.
                   leaf juices

             Lepidoptera (butterflies and moths, larvae
                       are caterpillars)

Cabbage          Larvae                  Green larva with white
  looper                                   stripes running
                                           lengthwise, looper-type
                                           movement, adult is a
                                           brown and gray moth.

Cabbage moth     Larvae                  Green larva, adult is cream
                                           colored moth. Big
                                           holes in leaves to
                                           complete defoliation.

Corn earworm     Larvae                  Tan to green striped
                                           caterpillars

European         Larvae                  Adult moth is cream to
  corn borer                               beige with brown
                                           markings.

Tomato/          Larvae                  Larva has green body with
  tobacco                                  conspicuous "horn" on
  hornworm                                 the rear end. Green
                                           frass, holes in leaves,
                                           leaves eaten down to
                                           the midrib, complete
                                           defoliation. Adult is a
                                           sphinx or hawk moth.

                 Orthoptera (crickets and grasshoppers)

Grasshoppers     Adult                   Hind pair of legs enlarged
                                           for jumping. Large fan-
                                           shaped back wings
                                           provide ability to
                                           appear to fly.

Mole cricket     Larvae and              Brown insect having two
                   adult?                  pairs of wings. Front
                                           pair of legs shaped for
                                           digging, just like a
                                           mole's.

                     Nematoda (various orders)

Nematodes        Adult                   Microscopic worm found
                                           in roots, stems, leaves.

                          Thysanoptera (thrips)

Thrips           Adult and larvae        Adult has slender pale to
                                           blackish minute body;
                                           color varies by species.
                                           Rasping mouthparts.

                              Dermaptera (earwigs)

Earwig           Adult                   Dark brown to black,
                                           narrow long body with
                                           conspicuous pincers
                                           on rear.

                 Stylommatophora (gastropods)

Snails and       Adult                   Slimy body with shell
  slugs                                    (snail) or lacking shell
                                           (slug) and having
                                           antennae.

                 AFFECTED PLANTS/
PEST             ORGANS

Mites            Stippled leaves on many
                   ornamental crops and
                   greenhouse crops.
                   Two-spotted and red
                   spider mites favor dry
                   or droughty
                   conditions.

Bean leaf        Beans of various species
  beetle           and corn. Larvae feed
                   on roots and other
                   underground plant
                   parts. Feeding damage
                   may girdle young
                   plants.

Colorado         Potato, tomato, eggplant,
  potato           pepper
  beetle

Cucumber         Chew holes and tunnel
  beetle           into roots, stems,
  (spotted         shoots, and leaves of
  and              cucurbits, beans, corn,
  striped)         peanuts, potatoes and
                   other vegetables.
                   Transmit bacterial wilt.

Japanese         Adults feed on ornamental
  beetle           plant foliage and
                   skeletonize leaves.
                   Larvae feed on roots of
                   living plants.

Various beetle   Feed on roots. Adults may
  grubs            emerge and feed, as
                   with Japanese beetle.
                   Are easily found by
                   digging in soil. May be
                   Japanese beetle, May
                   or June beetles.

Apple maggot     Maggots tunnel through
  fly              flesh of apples, pears,
                   and cherries. Egg
                   punctures in fruit may
                   be covered with white
                   wax.

Fungus gnat      Lay eggs in soil, larvae
                   hatch and feed on
                   roots, spread
                   pathogens, and may
                   enter stems to feed.

Leafminers       Foliage on a wide range of
                   host plants.

Aphids           Pinprick feeding holes;
                   honeydew encourages
                   sooty mold; can vector
                   viruses. Plant becomes
                   covered with aphids as
                   they give live birth
                   while feeding.

Chinch bug       Turfgrass species. Irregular
                   patches of turf turn
                   yellow and then die.
                   Adults and nymphs
                   feed on turf foliage in
                   mainly sunny areas.

Leaf hoppers     Plant juices of many
                   different plants and
                   crops, including
                   grasses, sedges,
                   broad-leafed woody
                   and herbaceous plants,
                   and conifers. Transmit
                   pathogens.

Mealybug         Many plants, major ones
                   are hibiscus, grapes,
                   foliage plants, flowers,
                   and vegetables. Found
                   on leaf nodes, leaves,
                   crotches, roots.
                   Honeydew results in
                   sooty mold.

Scales (soft     Orchard trees, ornamental
  and              shrubs; stems, leaves.
  armored)         Soft scales produce
                   honeydew and can
                   move during their life
                   cycle; armored scales
                   cannot.

Tarnished        Terminal flower shoots
  plant bug        punctured; flowers wilt
                   and die. Leaf bud
                   spotting, a general
                   bronzing on leaves.
                   Catfacing on fruit, fruit
                   drop on tree fruits and
                   vegetables.

Whiteflies       Many plants. Leaves. Eggs
                   laid on undersides of
                   leaves.

Cabbage          Plants in the Cruciferae
  looper           (mustard) family. All
                   parts of plant.

Cabbage moth     Plants in the Brassica
                   family. All parts of
                   plant.

Corn earworm     Corn, especially the ears;
                   tomato, gladiolus,
                   others.

European         Corn. Larvae bore into
  corn borer       stems, stalks of corn,
                   may cause lodging
                   (toppling over) due to
                   stem damage.

Tomato/          Tomato, tobacco, other
  tobacco          solanaceous plants.
  hornworm         They feed on foliage
                   and tomato fruits.

Grasshoppers     Irregular holes in leaves,
                   chewing at leaf margin.
                   Leaves may be eaten
                   down to the petiole or
                   midrib.

Mole cricket     Tunnels through roots of
                   turf grasses.

Nematodes        Hundreds of species of
                   ornamental and food
                   crops are affected.

Thrips           Hide in the flowers or
                   growing point of
                   leaves, feed on
                   developing leaves.
                   Vector viruses. Cause
                   ring-shaped blemishes
                   on citrus.

Earwig           Flowers, vegetables, fruits;
                   small, irregular holes in
                   leaves. Eats decaying
                   matter.

Snails and       Foliage of ornamental
  slugs            plants, hostas.
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Author:Loehrlein, Marietta M.
Publication:Home Horticulture: Principles and Practices
Date:Jan 1, 2008
Words:4868
Previous Article:Chapter 8: diseases.
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