Agricultural crops are under constant assault
by insect pests, making insecticides essential to reduce losses. Synthetic
insecticides such as organophosphates are important, effective tools in modern
crop management. However, they pose serious threats to the environment and to
people. Humans come in contact with dangerous pesticides on food, in water and
in the air near farms. This "pesticide drift" occurs when pesticide
dust and spray travel by wind to places unexposed to pesticides. Almost 98 percent
of sprayed pesticides do not reach their targets. They penetrate to
groundwater, pollute streams and harm wildlife, including natural predators of
the targeted pests. Biopesticides include "naturally occurring
substances that control pests (biochemical pesticides), microorganisms
that control pests (microbial pesticides), and pesticidal substances
produced by plants containing added genetic material.
Many farmers will not use synthetic
pesticides, and some consumers will only buy organic produce. Mass production
farms rely on synthetic pesticides, however, because they are cheaper than
organic ones. When farmers used pesticides such as DDT and Malathion, there was
little understanding of how dangerous and long-lasting these chemicals are. It
was only later that the degree to which these pesticides remain in the
environment was discovered (Carson). Organophosphates designed to affect the
brain and nervous system of insects, sometimes damage those of humans and
animals.
Pesticides in this group, for example rotenone, pyrethrum,
nicotine, neem oil, and all of the botanical
pesticides are products of living organisms. Often they are
chemicals that plants and microbes use to protect themselves from parasites,
predators and pathogens.
Nicotine, for example, is produced by plants
in the genus Nicotiana as a powerful herbivore (plant-feeding)
deterrent. Nicotine is also a potent insecticide and is highly toxic to
mammals. In small doses, delivered by smoking dried tobacco leaves, nicotine is
a stimulant. Organicpesticides are often lower in toxicity than older
synthetic pesticides but this is not always the case.
Major Categories:
· Botanical products
· Soaps and oils
· Minerals
· Biological agents
Botanical products
Neem
In addition to its categorization as a
botanical, neem is also plant-derived horticultural oil. The neem tree is
native to India and is the source of hundreds of products, including
insecticides made from the extracts of the seeds and bark. The primary insecticidal
extract is azadirachtin. When azadirachtin is used for pest management, it can
act as an insect repellant, an anti-feedant (interferes with feeding), and
growth regulator (interferes with molting and growth) .When neem oil or neem
soap is used, it poisons upon contact much like other soaps and oils. In some
cases, neem can also be a systemic insecticide (when applied to the soil, the
active ingredients are absorbed into the plant and transported to the growing
tips and leaves).
Pyrethrum
Pyrethrum, also known as pyrethrins, is
extracted from the seed of Chrysanthemum cinerariaefolium and has been used as
an insecticide for over 100 years. Today these plants are grown primarily in
Kenya. Pyrethrum is effective against a wide range of soft-bodied garden pests
such as scales, whitefly, mealybugs, and thrips, but will not control mites.
Pyrethrins are neurotoxins that attack an insect’s nervous system and cause
repeated and extended nerve firings. They may also have a repellant effect.
Fermented
Some microbes can be fermented to produce an
insecticide such as abermectins, a fermented product of Streptomyces used in
baits for household insect pests. The best known home gardening product of this
type is spinosad. Metabolites of Saccharopolyspora spinosa, a soil-inhabiting
bacteria that is fermented, are the basis for this new class of insecticide.
The fermentation process has been industrialized to produce commercial
insecticides.
Spinosad
Spinosad is composed of spinosyns A and D.
The fermented product is very toxic to caterpillar pests such as cabbageworm,
cabbage looper, diamondback moth, armyworm, and cutworm, as well as fruit flies
such as spotted wing drosophila. Spinosad can act on a susceptible insect’s
stomach and nervous system. It is primarily ingested by feeding insects but can
have some efficacy when sprayed directly on insects. Affected pests cease
feeding and undergo partial paralysis within minutes upon exposure to spinosad,
but it may take up to two days for the insects to die. Spinosad is systemic in
some plants.
Horticultural Oil
Dormant and Summer Oils. Dormant and
summer horticultural oils can control egg, nymph, larva, and adult stages of
overwintering leafrollers, aphids, mites, and scales. Dormant oils are
effective at controlling overwintering eggs and soft-bodied insects and can be
used in the early spring before active plant growth begins. Only use dormant
oils on woody trees and shrubs in dormant or delayed-dormant stages to avoid
severely burning the foliage. Do not apply either type of oil during freezing
weather because it will reduce the effectiveness of the oil properties and
coverage of the application.
Soaps and Oil
Natural soaps are derived from plants
(coconut, olive, palm, cotton) or animal fat (whale oil, fish oil, or lard) and
have been used since the 1700s to control certain soft-bodied insects such as
aphids.
Insecticidal Soaps
Insecticidal soaps are very effective for
managing soft-bodied insects like aphids, scales, whitefly, mealybugs, thrips,
and spider mites. The soap must contact the insect’s outer skeleton to be
effective. Leaf-feeding insects are often found on the undersides of leaves, so
be sure to fully cover plant foliage. Results from the application of soap are
usually seen in 1–3 days. Multiple applications are often needed to be
effective. Insecticidal soaps are usually diluted with water before applying.
Minerals
Insecticides developed from elemental
(mineral) sources mined from the earth are classified as natural products and
often cost less than other processed or harvested insecticides. The toxicity of
mineral-based insecticides depends on the chemical properties of the mined
elements. Some mineral insecticides such as sulfur are registered for organic
use and have relatively low toxic effects on people and nontarget organisms.
Diatomaceous Earth
Diatomaceous earth is a fine particle dust
comprised of fossilized diatoms that is effective against slugs and
soil-dwelling insects. Diatoms are small, usually single-celled phytoplankton
commonly found in aquatic or moist environments. Diatoms are encased inside a cell
wall made of silica, the same compound used to make glass. Diatomaceous earth
works as a fine abrasive that disrupts the exoskeleton cuticle of a slug or
insect and causes it to desiccate (dry out). Use diatomaceous earth only in
landscape areas that do not contain edible plants (e.g., ornamental gardens)
Elemental Sulfur
Elemental sulfur is a finely ground powder
that can be applied either as a dust or a spray. This mineral is one of the
oldest pesticides known, and reported pest resistance is rare. Sulfur acts as a
metabolic disruptor (interferes with a chemical reaction, digestion, or the
transport of substances into or between cells) to insects such as aphids,
thrips, and spider mites. Most sulfur formulations have low toxicity to people
but can be an eye and skin irritant. Sulfur is highly toxic to fish, so it is
important to keep it away from water.
Iron Phosphate
Iron phosphate is very effective at managing
slugs and snails when combined with bait. Baited iron phosphate usually comes
in pellet form. Scatter the product around the crop in need of protection and
areas where slugs seek refuge, such as garden bed borders and rocks. Liquid
formulations are also available. Follow label suggestions for subsequent
applications.
Kaolin
Kaolin is fine clay that is sprayed on plant
foliage or fruit to deter feeding and egg laying of insect pests such as apple
maggot, codling moth, and leafhoppers. It can also have some repellant
properties that cause irritation to insects upon contact. The effectiveness
only lasts as long as the clay film covers the fruit or foliage to mask its
chemical, visual, and tactile cues.
Living organisms that are used to manage
pests are called biological controls or biological agent. Now increasing
attention has been paid to the development of sustainable agriculture in which the high productivities of
plants and animals are ensured using their natural adaptive potentials, with a
minimal disturbance of the environment.
Biotechnology can also help in developing
alternative controls to synthetic insecticides to fight against insect pests. Microorganisms in the soil that will attack fungi,
viruses or bacteria, which cause root diseases. Formulas for coatings on the
seed (inoculants) which carry these beneficial organisms can be developed to
protect the plant during the critical seedling stage. Microorganisms found in
the soil are all not so friendly to plants. These pathogens can cause disease
or damage the plant. As scientists developed biological “tools,” which use these
disease-causing microbes to control weeds and pests naturally.
Bacillus thuringiensis (BT) is a naturally-occurring
bacterium that feeds on the larval stages of insect pests such as mosquitoes,
Colorado potato beetles, and cabbage loopers. Bt. var. kurstaki feeds on
Lepidopteran larvae, known as caterpillars, commonly found on vegetables and fruit.
Under natural conditions when a caterpillar ingests BT, the bacterium releases
a toxin within the insect’s gut, and the toxin degrades the stomach lining,
causing the insect to die.
Beauveria bassiana is a soilborne fungus that feeds on
insects and can be used effectively to control thrips, aphids, whitefly,
caterpillars, beetles, and subterranean insects like ants and termites. B.
bassiana is applied to the target pest as a spore, which is the reproductive
and dispersal structure of the fungus. Once the spores have contact with the
insect exoskeleton, they grow hyphae (long, branching vegetative appendages)
that secrete enzymes, which in turn dissolve the cuticle (outermost layer of
the skeleton). These fungal hyphae then grow into the insect, feed on its body
tissue, produce toxins, and reproduce. It takes up to seven days for the insect
to die.
Nematodes
Nematodes are multicellular organisms
commonly referred to as microscopic worms. Certain nematode species are
considered beneficial, as they are very effective at managing soil-dwelling
insect pests such as root weevils and cutworms, and can also control pests that
pupate or hibernate in the soil such as codling moth larvae.
Nosema
Nosema are protozoans (a diverse group of
single-cell organisms which can be highly mobile), that have proven to be
effective control agents for some insect pests. For example, Nosema locustae is used to manage grasshoppers. Nosema
spores are added to bait (also called an attractant) which the grasshopper
eats. The spores germinate and the protozoan’s feed within the insect’s body
cavity. As the protozoans reproduce, the insect’s health declines.
Even though farmers realize the importance of
using plant organic pesticides as alternatives to chemical pesticides, the
widespread use of these organic pesticides will take a while to become very
popular. One of the ways by which they can be popularized is to process it and
make it available to the farmers in a readily usable form.
