pest_management

University of Michigan Biological Station

Biology 442 - Biology of Insects

Lecture Notes - Pest Management

Pest problems and definition.
1. Pest - species that irritates or destroys something of value to humans. 200 serious, 450 occassional, 6,000 annoying.
  1. May act directly on plant and directly or indirectly on specific product.
  2. May be vector of disease.
  3. May be only irritation.
  4. Must remember that many more species are probably beneficial and many others innocuous.
2. Human contributions to pest problems.
  1. Ecosystem simplification and concentration, e.g. monoculture agriculture. 20% of corn crop (largest cash crop) is destroyed.
  2. Transportation of pests. Importation of pest, host or both, e.g. Colorado potato beetle, Gypsy moth, European corn borer, Cucumber beetle, African honey bee.
  3. Human attitudes and demands. We want perfect products, i.e. fruits, vegetables, etc.
3. How do we legislate control of pests?
  1. Quarantines - manditory restriction of importing and exporting. Border inspections. Cheaper than other methods.
  2. Eradication - total elimination of pest, very difficult, very expensive. Med-fly.
  3. Containment - Regular treatment and monitoring. Gypsy moth program.
  4. Suppression - knock back large populations or sudden outbreaks - like eradication with no hope of extinction and cheaper.
Methods of control.
1. Chemical control - method of choice over most of North America because they work rapidly and we can afford them.
  1. Advantages - effective, quick acting, readily available, relatively cheap.
  2. Disadvantages - kill non-target organisms, application may be dangerous, residues enter food chain, development of resistance
  3. History of chemical control.
    1. 1867 - Paris green (arsenic) used to kill potato beetle.
    2. 1910 - Federal Insecticide Act - to prevent fraud and protect farmers.
    3. 1938 - Food, Drug and Cosmetic Act - created FDA in response to As and Pb on fruit, to protect consumers - now transferred to EPA.
    4. 1939 - DDT discovered as insecticide, ushered in modern era.
  4. Things to consider about chemicals.
    1. Specificity.
    2. Persistence.
    3. Mode of action.
    4. Toxicity - LD50 value.
  5. Inorganics - CaAs and PbAs, once common, now not used.
  6. Botanicals - plant secondary compounds that kill insects. Generally degrade quickly and have low toxicity to mammals.
    1. Pyrethrum - Chysanthemum - topical application.
    2. Nicotine - Tobacco.
    3. Rotenone.
  7. Chlorinated hydrocarbons (organochlorines).
    1. DDT - used during WWII to kill human lice with no ill effects to soldiers. Used widely after war in mosquito spraying and other uses. Cheap and easy to make, killed insects well. Problems noticed after 10 years - pests started evolving resistance. After 15 years it was found to biologically magnify (in Lake Michigan: in mud 0.014 ppm, in arthropods 0.44 ppm, in fish 4.0 ppm, in birds 99 ppm - 7000 fold increase). These chemicals in general are very persistent and they are not soluable in water so they are retained in body. Weakening of egg shells of eagles and osprey. Banned in 1970 in U. S.
    2. Others include Lindain, Aldrin, Dieldrin, Chlordane (still used for termites).
  8. Organophosphates - many kinds and work many ways. They are similar to nerve gas in that they inhibit cholinesterase (neurotransmitter). They are less persistent and so have less evolution of resistant insects.
    1. Diazinone.
    2. Parathion.
    3. Malathion - medfly program.
  9. Carbamates - cholinesterase inhibiters, short lived. Oils - goo up plants.
  10. Problems with use of chemicals.
    1. Evolution of resistance with pest resurgence. Caused by target species evolving resistance and natural enemies still dying due to the chemical - many examples
    2. Secondary pest outbreaks - control primary host and previously contained host may appear as most important - red-banded leaf roller
    3. Health problems.
2. Plant breeding for host resistance - plant genetics. Done consistently with crop plants can stay about 5 years ahead of the insects. Try to create non-preference, antibiosis or tolerant strains (corn earworm, hessian fly). Genetic engineering may become important soon.
3. Cultural control (ecological control) - involves things such as tillage (weeding that destroys potential pests), crop rotation, fallowing, mixed cropping, timing of planting and harvesting, sanitation, trap crops.
4. Autocidal techniques. Sterile male release - worked with screwworm fly (Calliphoridae), but often doesn't.
5. Chemical mediation of behavior. Includes feeding deterents and repellents. Sex pheromones (have not been successful except in monitoring). Growth regulators (juvenile hormone - culturing with New York Times).
6. Biological control - use of predators, parasites and pathogens. Perhaps least invasive.
  1. Introduction of exotic enemies - only works for introduced pests (cottony cushion scale introduced into California from Australia in 1860 and became severe pest; 1888 brought in Vadalia beetles and outbreak was controlled).
  2. Conservation - avoid destroying natural enemies by various techniques including providing nectar sources and alternate hosts.
  3. Augmentation - Breed and release large numbers of predators or parasites into natural population.
  4. Use of pathogens.
    1. Viruses - good because very specific but expensive to produce, easy to apply (Gypsy moth).
    2. Bacteria - best example Bacillus thuriengensis (BT) for control of lepidopterous larvae (Gypsy moth); good because it is a spore former. Japanese beetle also has Bacillus that kills it.
    3. Fungus - difficult because it depends heavily on weather conditions. Aphids in greenhouse can be controlled with a fungus.
    4. Protozoa - Nosema locustae, grasshopper parasite.
    5. Nematodes - may be a possible control for mosquitoes, but must be cultured in the larvae.
  5. Control of weeds using insects - Opuntia cactus in Australia and Cactoblastis moth; Klamath weed in California and Chrysomelid beetle.
7. Integrated Pest Management. Very popular concept now. Uses aspects of many types in a sophisticated manner. Costly and hard to implement but mostly ecologically sound. - example: cotton - use varieties that are disease resistant and cold tolerant so they can be planted early and miss most pests. Crop residues treated or destroyed to kill diapausing weevil larvae. Predators and parasitoids are encouraged including BT. Pheromones are available. Sterile male release has been used to some extent with boll weevil. Some chemicals still sprayed, but more selectively.

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