Virginia Tech
FOR 4524 - Pest and Stress Management of Trees
Exam 2 - April 9, 2001
Name: KEY SS#
Entomology Section:
Please read all questions carefully. Numbers in boldfaced parentheses represent how many points a section is worth and if not boldfaced, the number of points each question or subquestion is worth.
Instructions: Circle the correct answer. (16)
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1. |
Some plants can produce juvenile hormone mimics to protect themselves from feeding insects. |
a. True |
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b. False |
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2. |
Insect blood is not involved in respiration. |
a. True b. False |
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3. |
Sawfly caterpillars can be used to heal persistent sores and wounds in humans. |
a. True b. False |
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4. |
Mandibles are found in millipedes and centipedes. |
a. True b. False |
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5. |
Even though mosquitoes develop in aquatic systems, they go through complete metamorphosis. |
a. True b. False |
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6. |
Although the number of insect species is enormous, it is still smaller than the number of all other species of non-insect arthropods. |
a. True b. False |
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7. |
Chiggers that bite you on your legs in the forest and drive you crazy are actually immature spiders. |
a. True b. False |
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8. |
Ticks and mites are both in Class Arachnida, Order Acari . |
a. True b. False |
Match the following words with the correct descriptions. (8)
9._C__ One pair of wings A. Coleoptera
10._B__ piercing/sucking mouthparts B. Homoptera
11.__D_ social insects C. Diptera
12.__A__ chewing only mouthparts D. Isoptera
Contrast the differences between: (16) - Be as complete as you can
13. spider mites and spiders
Spider mites are true mites that feed on plants and produce webbing around where they feed . Spider produce webs but do so to catch prey. Spiders are in a different Order than mites.
14. parasite and parasitoid
A parasite lives off of another organism, but usually doesn’t kill it. Parasitoids are special term for insects that parasitize other insects and whose progeny do kill their prey.
compound eyes are made up of individual ommatidia (lenses) that allow the insects to view movement, objects, and colors. Ocelli are simple eyes that help the insect assess environmental conditions like photoperiod. This can be used for inducing or breaking diapause.
16. incomplete and complete metamorphosis
More primitively evolved insects go through incomplete metamorphosis, where no pupal stage occurs and immature nymphs resemble the adult stage. For complete metamorphosis, insects pupate and the immature stages are vastly different physically and in function to the adults.
17. constitutive and induced tree resistance
Constitutive resistance is where plants already have barriers in place to thwart foreign organisms (ie. Resin in the stem, spines on the twigs). Induced is where the plant responds to invasions and creates chemicals that are used for defense. An example comes from trees that try to wall off an invasion from fungi or insects.
Diapause is a dormant state that is induced by specific environmental conditions, usually in advance of adverse condition. Quiescence is the shutting down of an insect’s metabolism, only at specific times when environmental conditions are unfavorable. They can snap out of that state as soon as conditions become favorable again. Not so w/ diapause.
In general sucking insects have less of an impact in the forest than in an urban environment. Except for some spectacular exotic pests, sucking insects are opportunists that take advantage of plants under stress. We know the urban environment is not normal for most plants. Conditions such as soil compaction, water stress, mechanical damage, bad climate match, and high use of insecticides (that kill predators) can lead to problems from insects like aphids and scales.
20. Phytotoxemia and induced hormone production resulting from sucking insects.
Phtytoxemia are disease-type symptoms that trees produce when attacked by sucking insects, such as leaf curling and spotting. Sometimes insects saliva in plants stimulates the plants to produce hormones that result in abnormal growth such as gall production. Insects then can use this abnormal growth to their advantage.
Provide complete and clear answers for the following questions.
21. Explain the concept of degree-days with respect to insects. Specifically, answer the following: (18)
A. Define degree-days (3)
Temperature development units for insects that are related to temperature and the insect’s low temperature development threshold. They accumulate on a per day basis.
Insects are cold-blooded. This means that rate of development is directly related to temperature. It is unique for each insect, species but also measurable for each insect species.
C. How do you determine the number of degree-days needed for a lifestage to develop? (5)
Development rate of a specific lifestage is examined at different constant temperatures. This usually results in a positive linear relationship between temperature and insect development rate. The inverse of the slope of the linear relationship reflected in a regression equation technically equals the number of degree days it takes for the median of a population to reach the next lifestage.
D. Describe how you would calculate degree-day accumulation in the field. (4)
The low temperature development threshold serves as the basis. For each day, the mean temp above the low threshold equals the number of degree days accumulated for that day.
E. How can this be used as a tool in pest management? (3)
Temperature can be monitored daily and prediction of the occurrence of a lifestage can be made by matching degree-day accumulation with already determined degree-day requirements for that insect's lifestage.
22. From the white pine weevil website out of British Columbia, describe the following for white pine weevil: (10)
A. Its life cycle (4)
One generation per year. Adults emerge from soil in the spring. They go to the leaders of young trees 3 - 15 years, mate and then the females oviposit in the bark of theleaders. The result brood of grubs begin feeding on phloem under the bark and feed together as the move down the leader. They will eventually bore into the stem to pupate and emerge as adults in the late summer. The adults overwinter in the soil.
B. What kind of damage results from attacks? (2)
Last year's leader is killed and this year's leader is killed as well. This causes forking and bushiness in the tree.
C. What are the different mortality agents of the weevil, and which one is considered the "key factor"? (4)
Winter mortality of adults is the key agent, probably from cold temperatures. Natural enemies such as parasitoids and predators also kill the weevil. Tree resin also kills some attacking weevils as well.
23. Describe and contrast each specific gypsy moth treatment tool we discussed in class. Do so in terms of:
efficacy -
host specificity -
difficulty in use or production
environmental hazards
situations where its use would be most appropriate.
As a hint I count the following tools: 3 biological microorganisms, several pesticides, and a synthetic form of a gypsy moth-produced product. (20)
Pesticides include Dimilin, carbamtes, and organophosphates. Of these, Dimilin is the best because it is not toxic to humans or other mammals. It is a chitin inhibitor that disables the insect's ability to molt. But it affects all arthropods. Therefore use in sensitive environmental areas is highly discouraged. All are effective, but the side effects are too great.
B.t. is a bacteria specific to Lepidoptera. It is an effective tool that is also environmentally sensitive. However, other Lepidopteran insects that are not targeted are susceptible as well. This is often an acceptable risk as B.t. is fast becoming the most commonly used control tactic in the U.S.
NPV (nuclear polyhedrosis virus), is specific to gypsy moth and is highly efficacious. Its major problem is the expense of producing it. It must be produced in vivo and is very labor intensive. Private industry won't touch this even if the Forest Service handed over the rights.
Entomophaga maimaiga is a species-specific fungus that has been brought to the U.S. from Europe. It appears to have taken off as a mortality agent in the 1990's and is attributed with the decline of gypsy moth in the mid-1990's. Its success is highly dependent on moisture and temperature conditions. It is not applied per se but is now part of the environment and will influence gypsy moth populations to various degrees in years to come.
The pheromone , Disparlure is a long chained alkane. It is produced by females and attracts males. It is used to survey for GM males in the summer to help assess populations for the following spring. It is also used in low GM density areas for mating disruption. This is an effective and environmentally sensitive tool to use under the right conditions.
24. Your parents call you up and ask for help on diagnosing a problem with their hemlock trees. There are numerous white marks at the base of the needles on most of the twigs. You say, "oh, I just learned about that in class." You want to demonstrate that the money they're investing in your education is being well spent so you describe the essence of the problem: what is the causal agent, why is it here, which trees tend to be susceptible, what can be done for treatment in the landscape setting, and what research is being carried out to address the problem in the forest setting? (12)
Causal agent is hemlock woolly adelgid
It is native to Asia and was introduced into the eastern U.S. in 1952 on exotic hemlock plants introduced into Maymont park in Richmond, VA. It has since spread in eastern hemlock's natural habitat, and is expanding its range every year.
Eastern and Carolina hemlocks of all ages are susceptible. Western hemlock and Asian hemlock species are resistant to attack.
Insecticides are effective in the landscape setting. Treatments include foliar sprays of dormant oils and systemic sprays of Merit.
Biological Control research is being carried out for forest settings. Predators have been introduced into the eastern U.S. They are all beetles. One is being released and the other four will likely be released in the near future.