General information Regarding invertiberates

1. Invertebrates are those animals without a backbone (spinal column). Invertebrates
include animals such as insects, worms, jellyfish, spiders - these are only a few of the
many types of spineless creatures.
Invertebrates are useful animals to study because their nervous systems work the
same way as that of vertebrates. Neuronsin all animals work using
an electrochemical process. It is easier to study the function of the more simple
nervous systems of invertebrates.
ights, Camera, Action Potential
This page describes how neurons work. I hope this explanation does not get too
complicated, but it is important to understand howneurons do what they do. There are many details,
but go slow and look at the figures.
Much of what we know about how neurons work comes from experiments on
the giant axon of the squid. This giant axon extends from the head to the tail of the squid and is used
to move the squid's tail. How giant is this axon? It can be up to 1 mm in diameter - easy to see with
the naked eye.
Neurons send messages electrochemically. This means that chemicals cause an electrical signal.
Chemicals in the body are "electrically-charged" -- when they have an electrical charge, they are
called ions. The important ions in the nervous system are sodium and potassium (both have 1
positive charge, +), calcium (has 2 positive charges, ++) and chloride (has a negative charge, -).
There are also some negatively charged protein molecules. It is also important to remember that
nerve cells are surrounded by a membrane that allows some ions to pass through and blocks the
passage of other ions. This type of membrane is called semi-permeable.
Resting Membrane Potential

2. When a neuron is not sending a signal, it is "at rest." When a neuron is at
rest, the inside of the neuron is negative relative to the outside. Although the concentrations of the
different ions attempt to balance out on both sides of the membrane, they cannot because the cell
membrane allows only some ions to pass through channels (ion channels). At rest, potassium ions
(K+) can cross through the membrane easily. Also at rest, chloride ions (Cl-)and sodium ions (Na+)
have a more difficult time crossing. The negatively charged protein molecules (A-) inside the neuron
cannot cross the membrane. In addition to these selective ion
channels, there is apump that uses energy to move three sodium ions out of the neuron for every
two potassium ions it puts in. Finally, when all these forces balance out, and the difference in the
voltage between the inside and outside of the neuron is measured, you have theresting potential.
The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the
inside of the neuron is 70 mV less than the outside. At rest, there are relatively more sodium ions
outside the neuron and more potassium ions inside that neuron.
Action Potential

3. The resting potential tells about what happens when a neuron is at rest. Anaction potentialoccurs
when a neuron sends information down an axon, away from the cell body. Neuroscientists use other
words, such as a "spike" or an "impulse" for the action potential. The action potential is an explosion
of electrical activity that is created by a depolarizing current. This means that some event (a
stimulus) causes the resting potential to move toward 0 mV. When the depolarization reaches about
-55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this
critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an
action potential of a fixed sized will always fire...for any given neuron, the size of the action potential
is always the same. There are no big or small action potentials in one nerve cell - all action
potentials are the same size. Therefore, the neuron either does not reach the threshold or a full
action potential is fired - this is the "ALL OR NONE" principle.
Action potentials
are caused when different ions cross the neuron membrane. A stimulus first causes sodium
channels to open. Because there are many more sodium ions on the outside, and the inside of the
neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has
a positive charge, so the neuron becomes more positive and becomes depolarized. It takes longer
for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the
depolarization. Also at about this time, sodium channels start to close. This causes the action
potential to go back toward -70 mV (a repolarization). The action potential actually goes past -70 mV
(a hyperpolarization) because the potassium channels stay open a bit too long. Gradually, the ion
concentrations go back to resting levels and the cell returns to -70 mV.
And there you have it...the Action Potential
http://www.epa.gov/caddis/ssr_ins_int.html

4. Figure 1. U.S. insecticide use in 2001 in millions of acres. PYR=pyrethroid, CARB=carbamate,
OP=orthophosphate.
Courtesy of USDA Agricultural Chemicals and Production Technology: Pest Management
Insecticides are chemicals used to control insects by killing them or preventing them from engaging in
behaviors deemed undesirable or destructive. They are classified based on their structure and mode of
action. Many insecticides act upon the nervous system of the insect (e.g., Cholinesterase (ChE) inhibition)
while others act as growth regulators or endotoxins. Table 1 lists the major classes of insecticides and
their modes of action. Understanding these modes of action can aid in the identification of a candidate
cause—particularly when enzyme assays or similar tests are used in symptom identification of affected
organisms.
Figure 2. A crop duster airplane spraying a field with insecticides. Aerial drift of insecticides can cover long
distances depending on wind and other factors.
Courtesy of U.S. EPA.
Insecticides are commonly used in agricultural, public health, and industrial applications, as well as
household and commercial uses (e.g., control of roaches and termites). The most commonly used
insecticides are the organophosphates, pyrethroids and carbamates (Figure 1). The USDA (2001) reported
that insecticides accounted for 12% of total pesticides applied to the surveyed crops. Corn and cotton
account for the largest shares of insecticide use in the United States.
Insecticides are applied in various formulations and delivery systems (e.g., sprays, baits, slow-release
diffusion; see Figure 2) that influence their transport and chemical transformation. Mobilization of
insecticides can occur via runoff (either dissolved or sorbed to soil particles), atmospheric deposition
(primarily spray drift), or sub-surface flow (Goring and Hamaker 1972, Moore and Ramamoorthy 1984).
Soil erosion from high intensity agriculture, facilitates the transport of insecticides into waterbodies
(Kreuger et al. 1999). Some insecticides are accumulated by aquatic organisms and transferred to their
predators. Insecticides are designed to be lethal to insects, so they pose a particular risk to aquatic
insects, but they also affect other aquatic invertebrates and fish.

5. Table 1. Insecticide types and their modes of action [from Radcliffe et al. (2009)].
Insecticide Type Mode of Action
Organochlorine Most act on neurons by causing a sodium/potassium imbalance preventing normal
transmission of nerve impulses, while some act on the GABA (γ-aminobutyric acid)
receptor preventing chloride ions from entering the neurons causing a
hyperexcitable state characterized by tremors and convulsions; usually broad-
spectrum insecticides that have been taken out of use.
Organophosphate Cause acetylcholinesterase (AChE) inhibition and accumulation of acetylcholine at
neuromuscular junctions causing rapid twitching of voluntary muscles and
eventually paralysis; broad-range insecticide, generally the most toxic of all
pesticides to vertebrates.
Organosulfur Exhibit ovicidal activity (i.e., they kill the egg stage); used only against mites with
very low toxicity to other organisms.
Carbamates Cause acetylcholinesterase (AChE) inhibition causing central nervous system effects
(i.e. rapid twitching of voluntary muscles and eventually paralysis); very broad
spectrum toxicity and highly toxic to fish.
Formamidines Inhibit the enzyme monoamine oxidase that degrades neurotransmitters causing an
accumulation of these compounds; affected insects become quiescent and die;
used in the control of OP and carbamate-resistant pests.
Dinitrophenols Act by uncoupling or inhibiting oxidative phosphorylation preventing the formation
of adenosine triphosphate (ATP); All types have been withdrawn from use.
Organotins Inhibit phosphorylation at the site of dinitrophenol uncoupling, preventing the
formation of ATP; used extensively against mites on fruit trees, formerly used as
an antifouling agent and molluscacide; very toxic to aquatic life.
Pyrethroids Acts by keeping open the sodium channels in neuronal membranes affecting both
the peripheral and central nervous systems causing a hyper-excitable state causing
such symptoms as tremors, incoordination, hyperactivity and paralysis; effective
against most agricultural insect pests; extremely toxic to fish.
Nicotinoids Act on the central nervous system causing irreversible blockage of the postsynaptic
nicotinergic acetylcholine receptors; used in the control of sucking insects, soil
insects, whiteflies, termites, turf insects, and the Colorado potato beetle; have

6. Table 1. Insecticide types and their modes of action [from Radcliffe et al. (2009)].
Insecticide Type Mode of Action
generally low toxicity to mammals, birds and fish.
Spinosyns Acts by disrupting binding of acetylcholine in nicotinic acetylcholine receptors at
the postsynaptic cell; effective against caterpillars, lepidopteran larvae, leaf miners,
thrips, and termites; regarded for its high level of specificity.
Pyrazoles Inhibits mitochondrial electron transport at the NADH-CoQ reductase site leading
to disruption of ATP formation; effective against psylla, aphids, whitefly and thrips;
results of testing on one type (fipronil) indicate no effects on the clams, oysters, or
fish, with marginal effects on shrimp.
Pyridazinones Interrupt mitochondrial electron transport at Site 1; mainly used as a miticide;
display toxicity to aquatic arthropods and fish.
Quinazolines Acts on the larval stages of most insect by inhibiting or blocking the synthesis of
chitin in the exoskeleton; developing larvae exhibit rupture of the malformed
cuticle or death by starvation; not registered in U.S.
Botanicals Depending upon the type can have various effects:
Pyrethrum – affects both the central and peripheral nervous systems, stimulating
nerve cells to produce repetitive discharges and eventually leading to paralysis;
commonly used to control lice.
Nicotine – mimics acetylcholine (Ach) in the central nervous system ganglia,
causing twitching, convulsions and death; used most to control aphids and
caterpillars.
Rotenone – acts as a respiratory enzyme inhibitor; used as a piscicide that kills all
fish at doses non-toxic to fish food organisms.
Limonene – affects the sensory nerves of the peripheral nervous system; used to
control fleas, lice, mites, and ticks, while remaining virtually non-toxic to warm-
blooded animals and only slightly toxic to fish.
Neem – reduces feeding and disrupts molting by inhibiting biosynthesis or
metabolism of ecdysone, the juvenile molting hormone; commonly used against
moth and butterfly larvae.
Synergists/Activators Inhibit cytochrome P-450 dependent polysubstrate monooxygenases (PSMOs)
preventing the degradation of toxicants, enhancing the activity of insecticides when
used in concert; synergists and activators are not in themselves considered toxic or
insecticidal.

7. Table 1. Insecticide types and their modes of action [from Radcliffe et al. (2009)].
Insecticide Type Mode of Action
Antibiotics Act by blocking the neurotransmitter GABA at the neuromuscular junction; feeding
and egg laying stop shortly after exposure while death may take several days; most
promising use of these materials is the control of spider mites, leafminers and
other difficult to control greenhouse pests.
Fumigants Act as narcotics that lodge in lipid-containing tissues inducing narcosis, sleep or
unconsciousness; pest affected depends on particular compound.
Inorganics Mode of action is dependent upon type of inorganic: may uncouple oxidative
phosphorylation (arsenicals), inhibit enzymes involved in energy production, or act
as desiccants; pest group depends on compound (e.g., sulfur for mites, boric acid
for cockroaches).
Biorational Grouped as biochemicals (hormones, enzymes, pheromones natural agents such as
growth regulators) or microbials (viruses, bacteria, fungi, protozoa and
nematodes), acting as either attractants, growth regulators or endotoxins; known
for very low toxicity to non-target species.
Benzoylureas Act as insect growth regulators by interfering with chitin synthesis; greatest value is
in the control of caterpillars and beetle larvae but is also registered for gypsy moth
and mushroom fly; some types are known for their impacts on invertebrates
(reduced emergent species) and early life stages of sunfish (reduced weight) (Boyle
et al. 1996).
Top of page

8. Figure 3. A simple conceptual diagram illustrating causal pathways, from sources to impairments, related to
insecticides. Click on the diagram to go to the Conceptual Diagrams tab and view a larger version.
Checklist of sources, site evidence and biological effects
Insecticides should be listed as a candidate cause when potential human sources and activities, site
observations, or observed biological effects support portions of the source-to-impairment pathways in
the conceptual diagram for insecticides (Figure 3). This diagram and some of the other information also
may be useful in Step 3: Evaluate Data from the Case.
The checklist below will help you identify key data and information useful for determining whether to
include insecticides among your candidate causes. The list is intended to guide you in collecting evidence
to support, weaken, or eliminate insecticides as a candidate cause. For more information on specific
entries, click on checklist headings or go to the When to List tab of this module.
Consider listing insecticides as a candidate cause based on the presence of the following sources and
activities, site evidence, or biological effects:
Sources and Activities
 Agricultural runoff
 Irrigation return water
 Tree farms and orchards
 Forestry application
 Mosquito control
 Insecticide manufacturing and storage
 Insecticide mixing and transfer to application equipment
 Urban and suburban runoff
 Combined sewer overflows (CSOs)
 Wastewater treatment plant discharges
Site Evidence
Site data for insecticides in water or sediment
Bioaccumulation of insecticides (e.g., in aquatic insects or fish tissue)
Biological Effects
 Mortality or developmental effects, especially in aquatic insects (Kreutzweiser
1997)
 Catastrophic or mass drift of aquatic insects (Kreutzweiser and Sibley 1991;
Beketovand Liess 2008)

9.  Reduced biological diversity (Relyea 2005), especially among aquatic insects
 Sudden, massive kills of aquatic life (e.g., fish kill in Mills River, NC)
 Fish exhibiting cough, yawn, fin flickering, S-and partial jerk, nudge and nip;
difficulty in ventilation and aberrant behavior (Alkahem 1996)
 Elevated muscle and liver pyruvate levels in fish (Alkahem 1996)
 Decr
Major classes[edit]
Organochlorides[edit]
The best-known organochloride, DDT, was created by Swiss scientist Paul Müller. For this
discovery, he was awarded the 1948 Nobel Prize for Physiology or Medicine.[5]
DDT was introduced
in 1944. It functions by opening sodium channels in the insect's nerve cells.[6]
The contemporaneous
rise of the chemical industry facilitated large-scale production of DDT and related chlorinated
hydrocarbons.
Organophosphatesand carbamates[edit]
Organophosphates are another large class of contact insecticides. These also target the insect's
nervous system. Organophosphates interfere with the enzymes acetylcholinesterase and
other cholinesterases, disrupting nerve impulses and killing or disabling the insect.
Organophosphate insecticides and chemical warfare nerve agents (such as sarin, tabun,soman,
and VX) work in the same way. Organophosphates have a cumulative toxic effect to wildlife, so
multiple exposures to the chemicals amplifies the toxicity.[7]
In the US, organophosate use declined
with the rise of substitutes.[8]
Carbamate insecticides have similar mechanisms to organophosphates, but have a much shorter
duration of action and are somewhat less toxic.[citation needed]
Pyrethroids[edit]
Pyrethroid pesticides mimic the insecticidal activity of the natural compound pyrethrum. These
compounds are nonpersistent sodium channel modulators and are less toxic than organophosphates
and carbamates. Compounds in this group are often applied against household pests.[9]
Neonicotinoids[edit]
Neonicotinoids are synthetic analogues of the natural insecticide nicotine (with much lower acute
mammalian toxicity and greater field persistence). These chemicals

10. are acetylcholine receptor agonists. They are broad-spectrum systemic insecticides, with rapid
action (minutes-hours). They are applied as sprays, drenches, seed and soil treatments. Treated
insects exhibit leg tremors, rapid wing motion, stylet withdrawal (aphids), disoriented movement,
paralysis and death.[10]
Imidacloprid may be the most common. It has recently come under scrutiny for
allegedly pernicious effects onhoneybees[11]
and its potential to increase the susceptibility of rice
to planthopper attacks.[12]
Ryanoids[edit]
Ryanoids are synthetic analogues with the same mode of action as ryanodine, a naturally occurring
insecticide extracted from Ryania speciosa (Flacourtiaceae). They bind to calcium channels in
cardiac and skeletal muscle, blocking nerve transmission. Only one such insecticide is currently
registered, Rynaxypyr, generic name chlorantraniliprole.[13]
Plant-incorporatedprotectants[edit]
Transgenic crops that act as insecticides began in 1996 with Bt potato that produces the Cry protein,
derived from thebacterium Bacillus thuringiensis, which is toxic to beetle larvae such as the Colorado
Potato Beetle. The technique has been expanded to include the use of RNA interference RNAi that
fatally silences crucial insect genes. RNAi likely evolved as a defense against viruses. Midgut cells in
many larvae take up the molecules and help spread the signal. The technology can target only
insects that have the silenced sequence, as was demonstrated when a particular RNAi affected only
one of fourfruit fly species. The technique is expected to replace many other insecticides, which are
losing effectiveness due to the spread of pesticide resistance.[14]
Insect growth regulators[edit]
Insect growth regulator (IGR) is a term coined to include insect hormone mimics and an earlier class
of chemicals, the benzoylphenyl ureas, which inhibit chitin(exoskeleton) biosynthesis in
insects. Diflubenzuron is a member of the latter class, used primarily to control caterpillars that are
pests. The most successful insecticides in this class are the juvenoids (juvenile
hormone analogues). Of these, methoprene is most widely used. It has no observable acute toxicity
in rats and is approved by World Health Organization (WHO) for use in drinking water cisterns to
combat malaria. Most of its uses are to combat insects where the adult is the pest,
including mosquitoes, several fly species, and fleas. Two very similar products,hydroprene and
kinoprene, are used for controlling species such as cockroaches and white flies. Methoprene was
registered with the EPA in 1975. Virtually no reports of resistance have been filed. A more recent
type of IGR is theecdysone agonist tebufenozide (MIMIC), which is used in forestry and other
applications for control of caterpillars, which are far more sensitive to its hormonal effects than other
insect orders.

11. Biological insecticides[edit]
Many plants exude substances to repel insects. Premier examples are substances activated by
the enzyme myrosinase. This enzyme converts glucosinolates to various compounds that are toxic
to herbivorous insects. One product of this enzyme is allyl isothiocyanate, the pungent ingredient
in horseradish sauces.
Biosynthesis ofantifeedants bythe action of myrosinase.
The myrosinase is released only upon crushing the flesh of horseradish. Since allyl isothiocyanate is
harmful to the plant as well as the insect, it is stored in the harmless form of the glucosinolate,
separate from the myrosinase enzyme.[15]
In general, tree rosin is considered a natural insecticide. To be specific, the production
of oleoresin by conifer species is a component of the defense response against insect attack and
fungal pathogen infection.[16]
Bacterialinsecticides[edit]
Bacillus thuringiensis is a bacterial disease that affects Lepidopterans and some other insects.
Toxins produced by strains of this bacterium are used as a larvicide against caterpillars, beetles, and
mosquitoes. Toxins from Saccharopolyspora spinosa are isolated from fermentations and sold
as Spinosad. Because these toxins have little effect on other organisms, they are considered
more environmentally friendly than synthetic pesticides. The toxin from B. thuringiensis (Bt toxin) has
been incorporated directly into plants through the use of genetic engineering. Other biological
insecticides include products based on entomopathogenic fungi (e.g., Beauveria
bassiana, Metarhizium anisopliae), nematodes (e.g., Steinernema feltiae) and viruses (e.g., Cydia
pomonella granulovirus).[citation needed]
Environmental effects[edit]
Effects on nontargetspecies[edit]

12. Some insecticides kill or harm other creatures in addition to those they are intended to kill. For
example, birds may be poisoned when they eat food that was recently sprayed with insecticides or
when they mistake an insecticide granule on the ground for food and eat it.[7]
Sprayed insecticide may drift from the area to which it is applied and into wildlife areas, especially
when it is sprayed aerially.[7]
DDT[edit]
Main article: DDT
The development of DDT was motivated by desire to replace more dangerous or less effective
alternatives. DDT was introduced to replace lead and arsenic-based compounds, which were in
widespread use in the early 1940s.[17]
DDT was brought to public attention by Rachel Carson's book Silent Spring. One side-effect of DDT
is to reduce the thickness of shells on the eggs of predatory birds. The shells sometimes become too
thin to be viable, reducing bird populations. This occurs with DDT and related compounds due to the
process of bioaccumulation, wherein the chemical, due to its stability and fat solubility, accumulates
in organisms' fatty tissues. Also, DDT may biomagnify, which causes progressively higher
concentrations in the body fat of animals farther up the food chain. The near-worldwide ban on
agricultural use of DDT and related chemicals has allowed some of these birds, such as
the peregrine falcon, to recover in recent years. A number of organochlorine pesticides have been
banned from most uses worldwide. Globally they are controlled via the Stockholm
Convention on persistent organic pollutants. These include: aldrin, chlordane,
DDT, dieldrin,endrin, heptachlor, mirexand toxaphene.[citation needed]
Pollinator decline[edit]
Insecticides can kill bees and may be a cause of pollinator decline, the loss of bees
that pollinate plants, and colony collapse disorder (CCD),[18]
in which worker bees from
a beehive or Western honey bee colony abruptly disappear. Loss of pollinators means a reduction
in crop yields.[18]
Sublethal doses of insecticides (i.e. imidacloprid and other neonicotinoids) affect
bee foraging behavior.[19]
However, research into the causes of CCD was inconclusive as of June
2007.[20]
Individual insecticides[edit]
Organochlorides[edit]
See also: Category:Organochloride insecticides
 Aldrin
 Chlordane
 Chlordecone
Pyrethroids[edit]
 Allethrin
 Bifenthrin
 Cyhalothrin, Lambda-cyhalothrin
 Cypermethrin

13.  DDT
 Dieldrin
 Endosulfan
 Endrin
 Heptachlor
 Hexachlorobenzene
 Lindane (gamma-hexachlorocyclohexane)
 Methoxychlor
 Mirex
 Pentachlorophenol
 TDE
Organophosphates[edit]
See also: Category:Organophosphate insecticides
 Acephate
 Azinphos-methyl
 Bensulide
 Chlorethoxyfos
 Chlorpyrifos
 Chlorpyriphos-methyl
 Diazinon
 Dichlorvos (DDVP)
 Dicrotophos
 Dimethoate
 Disulfoton
 Ethoprop
 Fenamiphos
 Fenitrothion
 Fenthion
 Fosthiazate
 Malathion
 Methamidophos
 Methidathion
 Mevinphos
 Monocrotophos
 Naled
 Omethoate
 Oxydemeton-methyl
 Parathion
 Parathion-methyl
 Phorate
 Phosalone
 Phosmet
 Phostebupirim
 Phoxim
 Cyfluthrin
 Deltamethrin
 Etofenprox
 Fenvalerate
 Permethrin
 Phenothrin
 Prallethrin
 Resmethrin
 Tetramethrin
 Tralomethrin
 Transfluthrin
Neonicotinoids[edit]
 Acetamiprid
 Clothianidin
 Imidacloprid
 Nitenpyram
 Nithiazine
 Thiacloprid
 Thiamethoxam
Ryanoids[edit]
 Chlorantraniliprole
 Cyantraniliprole
 Flubendiamide
Insect growthregulators[edit]
 Benzoylureas
 Diflubenzuron
 Flufenoxuron
 Methoprene
 Hydroprene
 Tebufenozide
Plant-derived[edit]
 Anabasine
 Anethole (mosquito larvae)[21]
 Annonin
 Asimina (pawpaw tree seeds) for lice
 Azadirachtin
 Caffeine
 Carapa
 Cinnamaldehyde (very effective for killing mosquito larvae)[22]
 Cinnamon leaf oil (very effective for killing mosquito larvae)[21]

14.  Pirimiphos-methyl
 Profenofos
 Terbufos
 Tetrachlorvinphos
 Tribufos
 Trichlorfon
Carbamates[edit]
 Aldicarb
 Bendiocarb
 Carbofuran
 Carbaryl
 Dioxacarb
 Fenobucarb
 Fenoxycarb
 Isoprocarb
 Methomyl
 2-(1-Methylpropyl)phenyl methylcarbamate
 Cinnamyl acetate (kills mosquito larvae)[21]
 Citral
 Deguelin
 Derris
 Derris (rotenone)
 Desmodium caudatum (leaves and roots)
 Eugenol (mosquito larvae)[21]
 Linalool
 Myristicin
 Neem (Azadirachtin)
 Nicotiana rustica (nicotine)
 Peganum harmala, seeds (smoke from), root
 Oregano oil kills beetles Rhizoperthadominica[23] (bug found in stored c
 Polyketide
 Pyrethrum
 Quassia (South American plant genus)
 Ryanodine
 Tetranortriterpenoid
 Thymol (controls varroa mites in bee colonies)[24]
Biologicals[edit]
 Bacillus sphaericus
 Bacillus thuringiensis
 Bacillus thuringiensis aizawi
 Bacillus thuringiensis israelensis
 Bacillus thuringiensis kurstaki
 Bacillus thuringiensis tenebrionis
 Nuclear Polyhedrosis virus
 Granulovirus
 Spinosyn A
 Spinosyn D
Other[edit]
 Diatomaceous earth
 Borate
 Borax
 Boric Acid