Insecticides 3 Flashcards
(29 cards)
what are botanicals, and what are the general properties?
natural insecticides derived from plants; easily metabolized, rapidly degraded in environment
Nicotine mech of tox?
nicotinic receptor agonist– mimics ACh at autonomic ganglia and NM junctions; has high affinity for synaptic ganglia (CNS) of insects; highly toxic to mammals (twitching/ CV collapse)
neonicotinoid insecticides general info
most widely used class of insecticides today; three chemical classes
three chemical classes of neonicotinoids?
n-nitroguanidines (e.g. imidacloprid); nitromethylenes (e.g. nitenpyram); N-cyanoamidines (e.g. acetamiprid)
mech of tox ac of neonics
nicotnic ACh receptor agonist; bind strongly and activate nic receptors; at low conc: nervus stimulation (e.g. muscle twitching, convulsions);
at high concs: nic receptor blockage that leads to paralysis and death
what are the advatanges of neonics?
low toxicity to vertebrates–>more selective for insect nic receptors; also effective against organisms resistant to OPs or carbamates;
they are also water soluble, which means they are readily absorbed by plants via roots and leaves–>this transports them through ALL of the tissues–>highly systemic activity–>can protect all parts of the plants from insect activity
flexible use–used as a seed dressing, foliar sprays, bait formulations, granular formulations, soil drench, inject into timber, and topically applied
possible economic benefits
disadvantages of neonics?
- absorption into target crop is very low–16-20% of the active ingredient in the seed dressing–>traditional sprays exceed 50% uptake;
- persistent in soil– different neonics will have different properties influencing persistence, but will mostly be persistent; soil type will also influence persistence; may have half lives of 200-1000 days
- potential for bioaccumulation;
may contaminate other environments (ground water, surround crops containing non-target plants) - Toxicity across taxa–insects are most sensitive but are gaining resistance–> birds are also sensitive; risks to granivorous verts
- impact on pollinators– neonics found in pollen and nectar–> affect bees, hoverflies, butterflies, etc
- Indirect ecological impact–>reduction in invert pops
rotenone general info—whre it’s produced, uses, toxicity, enviro kinetics
produced in roots of derris and lonchocarpus; used to control leaf-eating caterpillars; used in home and garden; used as a piscicide (neutralized by KMnO4); moderately toxic to mammals; rapidly photodegraded;
rotenone mech of ac?
strong inhibitor of ETC–>inhibs complex I of ETC (NADH DH complex); no ATP = no energy to keep up cell structure = oxidative stress
what is pyrethrum?
extract from flowers of tropical Chrusanthemum species –> a mixture of four compounds–> Pyrethin II and Cinerin I and II
pyrethrum general info–uses, kinetics, disadvantages
very unstable in sunlight, t1/2 = 8.5, 12-13h on soil; requires synergist (e.g. piperonyl butoxide) to be toxic; used in household insecticides sprays and pet products; has low mammalian toxicity
why is pyrethrum not very toxic to animals?
rapidly metabolized in animals; can cause allergic reactions in humans
what are the synergists of pyrethrum?
piperonyl butoxide and sesamex
piperonyl butoxide and sesamex general info?
not toxic/insecticidal by themselves–>inhibit CYP450 enzymes (pyrethrum would be inactivated by CYPs if they weren’t inhibited); these synergists only work with insecticides inactivated by CYPs
first gen pyrethroids time, e.g., and advantages
1949, allethrin, and more stable than parent, cinerin 1, but requires synergist
second gen pyrethroids time, e.g., and advantages
1965, tetramethrin, resmethrin (common in household sprays); greater efficacy but still requires synergist
third gen pyrethroids time, e.g., and advantages
1972, fenvalerate/permethrin; stable in sunlight and does not require a synergist;
first agricultural pyrethroids
fourth gen pyrethroids time, e.g., and advantages
1985; cypermethrin, decamethrin; photostable, long resisdual effect and high efficacy; no synergist needed
mech of ac of pyrethroids
all affect Na channels, but differently; Type 1 (1st and 2st gen)--> cause repetitive neural discharge (holds Na channels open for a longer than normal tim-->produces inappropriate APs/neuronal irritation) type 2 (3rd and 4th gen): no repetitive discharge; instead holds Na channels for an even longer time--> causes persistent depolarlization (inceases refractory period of the neuron, cause inappropriate firing firing, then prevents subsequent firing)
toxin produced Bacillus thuriningiensis (Bt)
used as insecticide; must be ingested to kill; alkaline gut activates the pro-toxin (good for us with our acidic gut –> non-target species not killed); gene for Bt toxin inserted genome of crops to kill insects that infects the crop;
three main serovarieties of the Bt toxin
kurstaki; israelensis; tenebrionis;
what is the kurstaki toxin used for?
used for lepidoptera larvae; ag, home, and forestry
what is the israelensis toxin used for?
selective for mosquitoes and blackfly larvae; some midges (type of black fly); applied directly to water where larvae are found
what is the tenebrionis toxic used for?
targeted for the colorado potater beetle
