Pesticides
There are over 40,000 different pesticide products on the market, involving more than 900 different active ingredients. An active ingredient means, of course, that it kills the pest, and an inert ingredient means that it does not kill the pest. However, inert ingredients do not necessarily mean they are harmless to humans! Thus, we have an overwhelming task in understanding this wide range of pesticides. The biological actions of pesticides can be characterized by "mode of action" in the following ways:
- stomach poisons must be ingested to take effect
- contact poisons are readily absorbed by the insect
- fumigants enter through the respiratory system
- dessicants act by cuticular abrasion, which basically erodes the insect's exoskeleton and causes dehdration
Many of the more modern pesticides act by multiple modes of action. To help sort through all these issues, we divide the active ingredients by their chemical characteristics as shown below.
A. inorganic pesticides are made from inorganic chemicals:
1. Boric acid powder: especially used for controlling roaches
(a stomach poison)
2. Sodium fluoride: also used for roaches
(also a stomach poison)
3. Paris Green: made from arsenic trioxide + copper acetate
(acts by multiple modes of action)
4. Silica gel (SiO2): a dessicant, it kills the bugs by drying them out
B. botanicals: many plant have evolved their own pesticides,
and humans have made effective use of
these "natural" pesticides
5. Pyrethrum from chrysanthemums, often used with
a synergist (i.e., combined with piperonyl butoxide)
synthetic forms are called pyrethroids
acts almost entirely as a contact poison
6. Rotenone roots of the Derris plant (a legume)
used as dusting powder for ticks on animals
synthetic forms are called rotenoids
acts as both a contact and stomach poison
7. Nicotine: usually nicotine sulfate
C. chlorinated
hydrocarbons: usually low toxicity, but high persistence in environment
8. DDT: dichloro diphenyl trichloroethane
9. others: mirex, endrin, dieldren, chlordane, BHC,
heptachlor, toxaphene
D. organophosphates: usually low persistence, but high toxicity
acetylcholinesterase inhibitor
10. Parathion,
Malathion (malathion is an exception,
being relatively low in toxicity)
11. DDVP (Dichlorvos)
Diazinon
E. carbamates: also an acetylcholinesterase inhibitor
12. Carbaryl (Sevin)
Aldicarb
Baygon
A. anticoagulants: multiple doses kill by internal bleeding in the rodent.
anticoagulants do not induce "bait shyness" (rodent
will not avoid it even after multiple feedings).
Furthermore, it has relatively low toxicity in humans.
1. warfarin low toxicity in humans,
but newer rat strains have developed resistance
2. others: pival, fumarin, PMP, diphacinone
Unlike the other rodenticides listed below,
B. botanicals: generally low toxicity to humans, botanicals can
induce "bait shyness"
3. Red squill: (from the plant)
a natural emetic (causes vomiting)
this is deadly in rats, because they cannot vomit
and instead choke and die (nasty but effective)
4. others bay leaves, cucumber skins
C. quick kill: extremely toxic to rats, but extremely toxic to
humans as well. If rats survive, they will have
"bait shyness"
5. 1080 (Sodium Fluoroacetate)
1081 (Sodium Fluoroacetamide)
only intended for registered pest controllers
6. others: Strychnine, Zinc phosphide, cyanide gas
ANTU (alpha naphtyl thiourea)
D. selective: Low toxicity to humans, highly toxic to Rattus genus,
but "bait shyness" can occur
7. Norbromide: vasoconstrictor
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8. evidence of droppings, burrows
rodents: gnawing marks (wood, cement, wires, etc.)
urine (shiny streaks under blacklight)
greasy runways (especially Rattus norvegicus)
9. other first, kill fleas (ectoparasite)
rodent controls: cement or steel curtains around house
to prevent burrowing
traps (traditional, or adhesive)
A. Alternative Pest Controls:
1. quarantine: control entry of fruits / vegetables across borders.
2. antifeedants/ irritants to surface feeding insects
repellants: no feeding = starvation (e.g., pyrethrum)
3. natural birds, spiders
predators: bacteria, viruses (e.g., Bacillus thuringiensis)
Gambusia affinis (eats mosquito larvae)
4. agricultural irrigation (e.g., minimize standing water)
practices: rotate crops (some crops are naturally resistant)
destroy crop residues (reduces food for pests)
5. natural
pesticides: (e.g., botanicals)
6. resistant
crop strains: (genetic engineering)
7. pheromones: sex attractants:
confuses males in locating females
only minute amounts needed (low toxicity)
complements the use of pesticide
8. juvenile internal chemicals that regulate growth
hormones: (e.g., eggs hatching to nymphs)
if we can synthesize juvenile hormones:
altered concentration = no development
low toxicity
difficult for pests to develop resistance
9. autocide: insect sterilization (usually U.V. radiation)
sterile males mate with fertile females
most effective when pest population is low
complements chemical methods (which are more
effective when pest population is high)
B. Laws:
10. FIFRA (1947): Federal Insecticide,Fungicide, and Rodenticide Act
registers pesticides, requires testing
The most toxic pesticides are labeled Danger.
11. FEPCA (1972): Federal Environmental Pesticides Control Act
allows EPA to regulate pesiticides
12. ToSCA (1977): Toxic Substances Control Act -- allows EPA to:
require information from chemical manufacturers,
test new chemicals for
environmental and health effects,
regulate chemicals not addressed by other laws.
Harmful chemicals at the earliest stages of production are defined and listed under TOSCA.
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