Chemical Control

1. Introduction
   1. Chemical control - preventative or remedial operations which depend for their effectiveness upon the chemical action or chemical properties of the substances used.
   2. Insecticides - substances which kill insects
      1. Classification by route of entry
         1. Stomach poisons
         2. Contact poisons
         3. Fumigants
      2. Classification by chemical nature or source of supply
         1. Inorganic compounds (natural and synthetic)
         2. Natural organic compounds (botanical -- alkaloids, rotenone, pyrethrins, neem)
         3. Synthetic organic compounds (organochlorines, cyclodienes, organophosphates, and carbamates)
         4. Insect growth regulators (hormones, hormone mimics, chitin synthesis inhibitors)
         5. Microorganisms (bacteria, viruses, fungi, nematodes)
2. History of Chemical Control
   1. 1200 B. C. - burning plants to kill insects by fumigation
   2. 19th Century (1800) to pre World War II
      1. Arsenicals and heavy metals (lead arsenate, calcium arsenate)
      2. Botanicals (nicotine = alkaloids, pyrethrum, rotenone, ryania)
   3. World War II
      1. Organochlorines and cyclodienes (DDT = dichloro-diphenyltrichloroethane, methoxychor, lindane, chlordane)
      2. Organophosphates (malathion, parathion, diazinon, chlorpyrifos)
      3. Carbamates (carbaryl, methomyl, temik)
   4. 1960s and 70s
      1. Synthetic pyrethroids (decamethrin, permethrin)
      2. Microorganisms (bacteria, viruses, fungi, protozoa, nematodes)
      3. Insect growth regulators (juvenile hormone, ecdysone, dimilin)
   5. 1980s and 90s (some are still experimental; "Goldilocks compounds))
      1. Avermectins (microbial by-products from bacteria)
      2. Synthetic nicotines (chlorinated derivatives) (imidacloprid)
      3. Phenyl pyrazoles (fipronil)
      4. Pyrroles
      5. Genetic engineering of microorganisms; Transgenic plants
      6. Bacillus thuringiensis toxin gene.
   6. Legislation of pesticides (later lecture)
3. Why Insecticides?
   1. Increase yield
   2. Greater production efficiency
   3. Many advantages (See V.)
4. Mode of Action of Insecticides
   1. Arsenicals - affect cellular respiration
   2. Chlorinated hydrocarbons - nerve poison (?); not really known
   3. Organophosphates and carbamates - nerve poison
   4. Insect growth regulators - disrupt molting and growth, or chitin synthesis
   5. Microorganisms - infection of tissues; toxins
   6. Nicotine derivatives and phenyl pyrazoles - nerve poisons
   7. Pyrroles - inhibit mitochondria; therefore affects energy production
5. Advantages of Chemical Insecticides (i.e., IV B and C)
   1. Broad spectrum
   2. Rapid mortality
   3. Inexpensive
   4. Easy to apply
   5. Persistent
   6. Stomach poison, contact poison, some fumigant activity
   7. Compatible with other chemicals (fungicides, other insecticides)
6. Disadvantages of Chemical Insecticides (i.e., IV B and C)
   1. Broad spectrum; adverse effects on nontarget arthropods
   2. Outbreak of secondary pests
   3. Persistent - environmental pollution
   4. Toxic to mammals; carcinogens
   5. Toxic to plants (phytotoxic)
   6. Pesticide treadmill
   7. Resistant populations (result of natural selection); cross-resistance;
      mixed function oxidase.
7. Pesticide Usage in the World
   1. Herbicides (47%)
   2. Insecticides (29%)
   3. Fungicides (19%)
   4. Nematicides, algicides, bactericides, avicides, rodenticides (5%)

Gullan and Cranston; Read: pp 403-407; 409-413.

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