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Horticulture Sample LessonHT230 Identifying Major Greenhouse Pests
MAIN IDEA: How can I identify the insects found in my greenhouse? When greenhouse scouts move through their routine of inspecting plants, checking traps and sticky cards, they must be able to identify the insects they observe. It is especially important to be able to recognize the major pests that are most likely to cause plant losses. MAJOR INSECT PESTS The following provides some guides to what scouts need to observe to be able to name the pests they see:
Aphids are small soft-bodied insects that are sometimes called plant lice. They are from 1/14th of an inch to 1/16th of an inch in length. They are sluggish and tend to cluster in colonies on the leaves and stems of the plants. Aphids are sucking insects that insert their beaks into a leaf or stem to extract plant sap. They are usually found on and under the youngest leaves where they prefer to feed. Aphids are the only insects that have a pair of cornicles, tubes that resemble exhaust pipes, at the rear of their abdomen. Winged aphids have two distinct dark spots on their wings. Feeding by aphids can cause leaves to curl or pucker.
Fungus gnats are small black flies, about 1/8 inch in length. Their legs and antennae are long in comparison to their bodies. They have tiny heads and one pair of clear wings. Females lay tiny ribbons of yellowish-white eggs in growing media that hatch within four days. The clear larvae are legless and have black heads. Fungus gnat adults are delicate insects with longer legs and antennae than shorefly adults. Adult fungus gnats have a distinctive "Y" shaped vein on their wings. Larvae mature underground in about 14 days and pupate near the surface of the medium. They construct a pupal case made of soil debris.
Shore flies look much like fungus gnats. The main differences are that shore flies have shorter antennae, red eyes and heavier dark bodies. By looking closely, you can see a pair of smoky wings with several clear spots on a shore fly. They fly well and you may find them on almost any surface in the greenhouse. Shore flies also look somewhat like winged aphids. Aphids, however, have the distinctive, tube-like cornicles on their abdomen, which shore flies do not have. The shore fly life cycle is similar to the life cycle of the fungus gnat. Larvae are yellow to brown in color, about 1/4-inch long, with no apparent head. Both larvae and adult shore flies feed on algae growing on media, floors, benches or pots.
Thrips are so small you will need to use a hand lens to tell the difference between thrips and specks of growing media on sticky card traps. Adult thrips are tiny, slender insects only about 1/25 inch long. Thrips have two pairs of wings fringed with a row of long hairs. Wings are held parallel over their body, flat against their back. Female thrips tend to be dark brown and slightly larger than the small tan or yellow males. Dark brown to black onion thrips may occasionally enter a greenhouse from outside. Thrips feed by rasping the plant surface and sucking up the exuding sap. Heavily infested leaves have a mottled or silvery appearance. Female thrips insert eggs into slits in the leaf. Eggs hatch in two to seven days. Nymphs feed much like adults and molt four times during development.
Whiteflies are powdery white insects, about 1/12 to 1/8 inch in length. You may see them flutter from the undersides of leaves when the plants are disturbed. The lower surface of the leaves may be infested with all life stages of whiteflies. Whitefly adults lose their white color when trapped on a sticky card and may appear to have an orangish cast. Three species of whiteflies may infest greenhouses. They are very similar and look very much alike to an untrained eye. They are not the same in biology, however, which may need to be considered when planning controls.
The whitefly is a sap-sucking insect. One female whitefly can lay 25 eggs per day up to a total of 150 eggs. The newly emerged crawler moves only a short distance before settling down to feed. After three larval molts, the pupal stage is formed, from which the adult emerges. The whitefly completes its entire life cycle in about 21 to 36 days.
Five types of mites may be found in greenhouses. They include the two-spotted spider mite, false spider mites, the cyclamen mite, the broad mite, and the bud and rust or eriophyid mite. Of these, the two-spotted spider mite and cyclaman mite are of the most concern to greenhouse crops. Mites are extremely small and difficult to see with the naked eye. Using a 10x magnification hand lens will help. However, you may need a dissecting scope to be able to identify cyclamen or broad mites.
OTHER INSECTS
The cutworm is one of several caterpillars that may be found in a greenhouse. Caterpillars are immature stages of moths. They chew on leaves, stems and fruits of many kinds of plants. Infestations may begin when moths enter through ventilators or when infested plants are brought into the greenhouse. Cutworms can be serious pests of younger plants. They hide in soil or mulch during the day and feed on the plants at night.
The cabbage looper is another caterpillar that may be found in some greenhouses. It is a pale green insect with three pairs of small fleshy bumps on the underside of the abdomen called prolegs. The looper moves by bringing the rear of its body up to the front legs before moving the front legs forward. This is similar to that of measuring worms. Loopers may be present if you see cut plants or leaves with large sections removed.
Leafminers are larvae of small flies that damage plants by feeding between the upper and lower surfaces of the leaf. Leafminers may be present when you see damaged areas on plants that are light in color, narrow and winding. Leafminers grow wider as the larva matures. Fully grown larva may pupate in the leaf tissue or emerge from the leaf and fall to the ground to pupate. Each female fly will lay from 50 to 100 eggs by inserting them into pits made in the leaf surface.
Mealybugs are much like aphids. They are soft-bodied insects that feed on plant sap. Mealybugs get their name from their thick covering of mealy or waxy secretions which provide some protection from contact insecticides. Some mealybugs lay eggs, while others give birth to live young. Mealybugs, like aphids, often excrete large amounts of a sweet, sticky substance called honeydew that results in sooty mold on leaves and other plant parts. EXERCISES: 1. Why would it be important for a crop scout to be able to identify insects that may be found in a greenhouse, but do not cause any significant damage? Discuss in class and/or write out an answer for your teacher. 2. Try to find living examples of pests covered by this lesson. You may be able to find them in a school greenhouse, on house plants or on a field trip to a local greenhouse operation. Ask your teacher for suggestions. Take notes on what you have found. Then discuss in class and/or write a report that answers the following:
3. Review the pest management practices you discussed for exercises in AgEdNet.com lessons HT227 Managing Greenhouse Insects and HT229 Guide to Scouting Greenhouse Pests. Remember, you imagined that you had become the owner of a greenhouse business, with managers and employees who take care of day-to-day operations at several locations. For this lesson, consider what you could do to help your managers and employees learn to identify insects. Then revise the written, working outline of the documentation you would need for the pest control work procedures you started when doing Exercise #4 in HT227 and HT229. What points would you need to cover to provide the instructions needed for scouts and those who manage your scouts? When you have finished, keep a copy of the revised outline. You will need to continue working with it in exercises for other greenhouse pest control lessons. INTERNET RESOURCES:
** Virginia Tech - Insect Identification Laboratory
** Iowa State University - Iowa State Entomology Image Gallery
** North Carolina State University - Photo Gallery of
Insects and Mites on Ornamental Plants
** University of Kentucky - IPM site
** West Virginia University Extension - Pest Management - Insects TEST:
Name the insect that fits each of the following descriptions. All insects described are from the 10 on the following list: aphids, cabbage loopers, cutworms, fungus gnats, leafminers, mealybugs, shore flies, spider mites, thrips and whiteflies. Some insects may be described more than once. Some insects may not be described at all. 1. Which white insects may turn orange on a sticky trap? 2. Which insects are so small you'll need a magnifying glass to see two pairs of wings fringed with a row of long hairs? 3. These soft bodied insects are sometimes call plant lice. 4. These small black flies have long antennae. 5. Name these legless clear larvae with black heads. 6. Which insects are small dark flies with short antennae and red eyes? 7. This is the only insect with a pair of cornicles, like exhaust pipes. 8. This powdery, 1/8-inch-long insect can be seen fluttering from the undersides of plant leaves. 9. These greenish bugs with distinctive black spots on their abdomens are so small you will need a 10x hand lens to see them. 10. This insect moves like a measuring worm.
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HT230 Identifying Major Greenhouse Pests
TEACHER'S GUIDEOBJECTIVE: Students will be made aware of the appearance, size and distinguishing characteristics of insects that are likely to be found in a greenhouse and that may cause damage to plants. They will have enough information to begin identifying some of the insects they find or trap when completing extension exercises. PREPARATION: Review lesson content and be prepared to help students carry out exercises. You may wish to coordinate this with insect trapping done for exercises for AgEdNet.com lesson HT229 Guide to Scouting Greenhouse Pests. Try to arrange time for them at a school greenhouse or with a local greenhouse operator who is willing to cooperate with your class. Consider the extension exercise suggested below. INTERNET RESOURCES:
** Virginia Tech - Insect Identification Laboratory
** Iowa State University - Iowa State Entomology Image Gallery
** North Carolina State University - Photo Gallery of
Insects and Mites on Ornamental Plants
** University of Kentucky - IPM site
** Virginia Polytechnic Institute, Insect Pests of Ornamental Plants
** West Virginia University Extension - Pest Management - Insects IMPORTANT TERMS: aphids, cornicles, cutworm, cyclamen mite, eriophyid mite, fungus gnats, hemoglobin, larva, larvae, larval, mealybugs, mites, molt, nymphs, pupa, pupate, pupal stage, shore flies, thrips, whiteflies. EXTENSION: Provide extra credit for students who search the Internet to find more on insect identification and write a report on what they have found that would be useful to a greenhouse manager. Using keywords "Insect.Identification" will bring up a wealth of sources. Helpful sites are listed under Internet Resources. EXERCISE ANSWERS: 1. Students should be able to recognize at least two reasons. One is to avoid using control measures when they are unnecessary. This could happen if the scout mistakes a harmless insect for one that may cause damage. Another is to avoid applying controls that may harm the populations of beneficial insects. 2. Answers depend on what opportunities are available to students, such as a school greenhouse, or a local greenhouse operator who is willing to cooperate with class activities. Insects may be found on plants, or on sticky cards or other traps used to monitor pest populations. Students who inspect plants should note what part of the plant insects were found on, such as on stems, under leaves, etc. Students could refer to lesson reference and drawings to help them identify pest species. They are likely to find it difficult to find pests and to distinguish between them. They may find insects not covered by this lesson that they cannot identify. The point: Students will be made aware of the need for training and experience to become competent at scouting, monitoring and managing greenhouse pests. 3. Students should be adding more detail on how employee scouts will be trained. It also might include suggestions for an ongoing training program. For example, a newer employee may be required to work with a more experienced scout to gain additional experience. In addition, the student's plan could include the building of a library of references with insect pictures and information employees could use to help them identify pests and gain experience. A great deal of information is available on the Internet, to help identify insects and to find identification services. Note that this draft outline will be used again in other lessons as students gain additional knowledge of greenhouse pest control methods. TEST KEY: Name the insect that fits each of the following descriptions. All insects described are from the 10 on the following list: aphids, cabbage loopers, cutworms, fungus gnats, leafminers, mealybugs, shore flies, spider mites, thrips and whiteflies. Some insects may be described more than once. Some insects may not be described at all. 1. Which white insects may turn orange on a sticky trap? Whiteflies 2. Which insects are so small you'll need a magnifying glass to see two pairs of wings fringed with a row of long hairs? Thrips 3. These soft bodied insects are sometimes call plant lice. Aphids 4. These small black flies have long antennae. Fungus Gnats 5. Name these legless clear larvae with black heads. Fungus Gnats 6. Which insects are small dark flies with short antennae and red eyes? Shore flies 7. This is the only insect with a pair of cornicles, like exhaust pipes. Aphids 8. This powdery, 1/8-inch-long insect can be seen fluttering from the underside of plant leaves. Whiteflies 9. These greenish bugs with distinctive black spots on their abdomen are so small you will need a 10x hand lens to see them. Spider mites 10. This insect moves like a measuring worm. Cabbage looper CROSSWORD PUZZLE ANSWERS:
Across: 1. Mealybugs, 6. Cabbage, 9. Shore, 10. Cutworm, 11. Thrips, 13. Cyclamen, 16. Whiteflies, 17. Silverleaf. END TEACHER'S GUIDE
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Aphids:
Fungus gnats:
Shore flies:
Thrips:
Whiteflies:
Mites:
Cutworm:
Cabbage looper:
Leafminers:
Mealybugs:
