Insect control Flashcards
What are the methods of inhibition?
- Physical removal (separation)
- Chemical destruction- insecticides
- Chemical deterrent
- Biological controls
- Genetic sterility
- Ionising radiation
- Gene transfer
- Environment manipulation
Tell me about the physicla removal (separation) techniques?
Bed net (good with flies but not good with crawling insects)
Net over face and whole body against midge/ biting fly (Culicoides Impunctatus Goetghebuer)
What are the major classes of insecticides?
Organochlorides
Phenyl pyrazole
Organophosphates and carbamates
Pyrethroids
Neonicotinoids
Ryanoids
What are the two types of Organochlorides insecticide groups?
DDT
Chlorinatedalicyclics
How do DDT work?
Block (open, agonist) peripheral NS Na+ channels
Preventing closure resulting in hyperexcitability of the nerve and later paralysis
Tell me a bit about DDT history
First synthesised in 1874 by Zeidler
Insecticide action discovered by Müller in 1939
Used in WWII to control malaria and typhyus among soldiers and in camps
Using in general agriculture
Where is DDT banned, how is it now used?
Banned in: Hungary, Norway, Sweden, Germany and UK
Today 3,314 tonnes produced for malaria and Leishmaniasis control via indoor residual spraying and for soaking bed and bed nets.
No longer used for outdoor environment (India)
Resistance is controlled
What is the DDT side effects to humans?
- Low level human carcinogen
- Endocrine disrupting
- Disruption in semen quality, menstruation, gestational length, and duration of lactation
What is DDT side effects to environment (silent spring)?
Persistent and toxic to insects and other invertebrates (crayfish, daphnids, sea shrimp)- hence destroys food webs (esp fish)
Because DDT concentration in the upper food chain is not broken down readily, why further effects can it cause?
Concentration in upper food chain as not broken down readily- e
ggshell thinning and population decline bird of prey inhibition of calcium ATPase in the shell gland (needed to calcify shells)
What are some examples of Chlorinatedcyclics?
Aldrin
Dieldrin
How do Chlorinatedalicyclics work?
block (closed) the GABA chloride complex, which inhibits chloride flow into the nerve, inhibit an inhibitor channel
Block the GABA chloride complex, which inhibits chloride flow into the nerve- blocking inhibitory CNS pathways
Tell me about the Aldrin and Dieldrin forms
Aldrin the inactive form is metabolised to Dieldrin- both high persistence
What are the side effects to the chlorinatedalicyclics?
NS damage- convulsions- long term exposure link to PD
An endocrine disruptor with immune effects- breast cancer, reproductive changes, acting an oestrogen, antiandrogen
A teratogen
Environmental
How does Phenyl pyrazole work?
Blocks (closed)- glutamate-activated chloride channels in insects (absent in mammals)
Also block the GABA chloride complex in insect CNS
Limits chloride flow into the nerve, blocking inhibitory CNS pathways lead to hyperexcitability
What are the environmental effects of phenyl pyrazole?
Environmental effects- also used a widespread insecticide (this is because they have a limited half-life)
What are some examples of organophosphates and carbamates?
Dichlorvos and Malathion
How do organophosphates and carbamates work?
block acetylcholinesterase (as do carbamates e.g., aldicarb)
How do organophosphates act as pesticides?
Organophosphate pesticides (related to nerve toxins-sarin)- irreversibly inactivate acetylcholinesterase- however there is varying affinity for vertebrate form
Why are organophosphates a better alternative to Organochlorides?
OPS hydrolyse rapidly (so tend to break down) so a better alternative to Organochlorides, but they have greater acute toxicity. Even at low levels, Ops may be hazardous to the brain development
Therefore;
OP= kill quick
OC= Long term effect
How are organophosphates used?
Residential use of organophosphates banned, still sprayed agriculturally on fruit and vegetables
Examples of organophosphates and Carbamates
How does Acetylcholinesterase work in the cholinergic system?
Acetylcholinesterase (AChE) is a cholinergic enzyme primarily found at postsynaptic neuromuscular junctions, especially in muscles and nerves. It immediately breaks down or hydrolyzes acetylcholine (ACh), a naturally occurring neurotransmitter, into acetic acid and choline
What long term effects does organophosphates/ carbamates cause that cannot be explained?
Neuropsychological performance significantly poorer
EEG tests poorer in exposed group
Pyrethroids are the artificial version, what are they based on?
Based on pyrethrin’s (natural) produced by Chrysanthemum cineraria folium
How is Pyrethroids used?
Main household insecticide
Pyrethrum has been used for centuries as an insecticide (lice treatment)
Relatively harmless to vertebrates and short lived
How do Pyrethroids work?
Block (open) axonal voltage-gated sodium channels so prevent repolarising and paralyse the organism
Tell me about second generation pyrethroids
Second generation more long lived but has greater off target effects and mammalian toxicity (dermatitis- CNS effects)
Examples of pyrethroids
What action do Neonicotinoids have?
Nicotine like action
Give an example of a neonicotinoid
Imidacloprid was the most widely used insecticide in the world
How do Neonicotinoids work?
Nicotinic acetylcholine receptor agonist in insect CNS
How do Neonicotinoids compare to organophosphates and carbamate insecticides?
Compared to organophosphate and carbamate insecticide neonicotinoids cause less vertebrate toxicity as differences in nicotinic receptor (Acetylcholinesterase’s more conserved)
What do low and high levels of neonicotinoids result in?
Low levels cause nervous stimulation
high levels block the receptor causing paralysis
Tell me some more facts about neonicotinoids
relatively long lived
Imidacloprid is effective against sucking insects (fleas), chewing insects on domestic animals
Role in off target bee losses- very low levels related to CNS effects reducing bees’ ability to forage, learn and remember navigation routes to and from food sources
What are ryanoids?
Alkaloid from south American willow
How do Ryanoids work?
Binds to ryanodine receptor, calcium channels in muscle (all 3 forms of muscle)
Agonist for the receptor causing released of calcium from the sarcoplasmic reticulum, leading to massive muscular contractions
What effect does ryanoids have in humans?
Has similar toxic effects on mammals- not well absorbed
Whats the artifical version of ryanoids?
Chlorantraniliprole- artificial versions show far greater insect specificity
Are ryanoids long or short acting?
Short acting
Name an inhibitor used for chemical inhibition
N, N-Diethyl-meta-toluamide
(DEET)
What is DEET used for?
Insect repellants, against mosquitos, ticks, fleas and other biting insects
What are two potential actions of how DEET works?
- Blocking insect olfactory receptors for 1-octen-3-ol, a volatile substance in human sweat and breath
- Binds to own receptor (IR40a) and in olfactory receptor in the antennae, explains inhibition in the absence of 1-octan-3-ol, (eucalyptol, linalool, and thujone act this way too)
Whats a genetic methods used?
Sterile insect technique
Tell me about the sterile insect technique
Provide examples of parasites it can be used against
Many biting insects mate only once- hence if overwhelming numbers of sterile males are released, these mate, and hence reduce the actively reproducing female population
Males usually sterilised with radiation
Repeated release of sterile males can diminish populations
- Screw-worm fly (feeds on cattle) in north America
- Tsetse fly in Africa (primary host for Trypanosoma- sleeping sickness and nagana) in Zanzibar
no residues
no (direct) effects on non-target species
What are some limitations to the sterile insect technique?
often needs chemical treatment to suppress population before the use of sterile insects
sex separation can be difficult, for screwworm- females also released (not a problem here but would be for species where female bite repeatedly and transmits disease e.g., mosquitoes)
radiation dose be correct- too high can reduce male mating fitness, insufficient fertile males released
the technique is species specific (22 Tsetse fly species)
the cost of producing sufficient sterile insects (20,000,000+) can be high
Whats an example of a gene transfer system?
The Tet suicide system
Tell me about the Tet suicide system
in presence of tetracycline- it binds to tetO7 and stopes expression of TAV gene
in absence of tetracycline- tetO7/hsp70 (heat shock protein 70) acts as a functioning promotor making tTAV (tetracycline-repressible transcriptional activator) which binds to the tetO7 promotor driving its own expression in an uncontrolled feedback loop
Hence with tetracycline you make you insects, then release them to mate in general population, now no tetracycline- takes roughly 5-10 days for the loop to dominate all transcription (so late acting lethality)- then these insects’ mate and lay eggs- they then die as do their grub offspring
“Non” sterile lethal male self-limiting system
Outcompetes any other proteins being produced
A positive feedback lethal system
Tell me about Gene drives
In normal sexual reproduction, each of the two versions of a given gene has a 50% change of being inherited by a particular offspring
Gene drives are genetic system that circumvent Mendelian rules:
They greatly increase the offs that the driven gene will be passed on to offspring, even if they reduce the change that each individual organism will then reproduce
Occur naturally but can now be engineered
Clustered regularly interspaces short palindromic repeat- CRISPR- Cas9 system
You can produce a plasmid with the guide RNA and the CRISPR gene on one plasmid
Donor RNA can be integrated which will remove guide region of DNA so MRNA can no longer bind
Can put longer sequences in to drive homologous recombination efficiently
If donor not inserted then it will keep being cut until something disrupts it
Can produce plasmif which contains sequence of guide RNA and CRISPR gene
Explain the gene drive system
Gene drive system
How can we use the gene drive system?
The gene drive previously explained is the ‘standard drive’, tell me about the other form, the ‘Daisy-chain drive’
Separate component
Make insects
Breed together
Make gRNA that will cut allele
CRISPS duplicates
Becomes homozygous which contains guide that will cut another allele further down with is also able to be homozygous
