Biological vs. Chemical Pest Control
All living things strive to survive, but unfortunately the needs of other creatures sometimes conflict with our needs. An example of this conflict is the struggle between pests and humans. Pests are creatures that injure or kill plants or domestic animals, transmit disease, cause economic damage or are a nuisance in some other way. They eat our food crops or ornamental plants, infect plants that are useful to us, make us sick by transmitting infectious organisms, infest our livestock and pets and destroy property. An effective form of pest control is essential if we're going to win the battle with pest organisms.
Many different chemicals are used to kill pests. These pesticides often work well, but since they're designed to kill living things they may cause serious problems in humans or pets. Pesticides contaminate the environment and the food that we eat and may enter our bodies when we're applying them to our plants or animals. They sometimes harm other organisms in addition to their target. Another problem with using chemicals to control pests is that a pest may become resistant to a pesticide.
Biological pest control involves the use of another living organism to kill a pest. No chemicals are needed, there is no environmental contamination with pesticides and the pests don’t become resistant to the control method. However, introducing a plant or animal to an area where it doesn’t normally occur can create new problems.
Types of Biological Pest Control
There are three types of biological pest control. In classical biological control, natural predators, parasites or pathogens of a pest are imported into an area to protect a crop or livestock. A "pathogen" is an organism that causes disease. Importation is a useful strategy when the pest has been introduced from another region and has no predators in its new habitat.
In conservation biological control no new plants or animals are introduced to an area, but the environment is manipulated to favor the survival of local enemies of the pest. For example, a farmer or gardener may provide additional food sources or suitable habitats for a pest's enemies.
In augmentation biological control, plants and animals which control a particular pest and are already present in an area are increased in number by inoculation or inundation. Inoculation is the introduction of relatively few organisms. Inundation involves the introduction of a very large number of organisms.
Advantages of Biological Pest Control
Biological pest control has some distinct advantages compared to chemical pest control. Farmers and gardeners don’t have to worry about poisoning themselves, their families or their pets when they treat their crops or plants. There are no toxic chemicals to store and no concerns about children or animals discovering the stored pesticides. There are no pesticides to give off dangerous vapors, accumulate in the soil or collect in water. The food that's produced will be free of pesticides (or low in pesticides, since the food may have picked up the pesticides distributed by other people).
Disadvantages of Biological Pest Control
Despite the appealing advantages of biological pest control there may be important disadvantages. Artificially increasing the population of a certain predator may have unforeseen consequences. In addition, an organism that has been introduced from another area to destroy a pest may become a pest itself, especially if it has no natural predators in its new habitat.
A famous example of this effect is the introduction of the cane toad into Australia. In 1935, cane toads were transported from Hawaii to North Queensland. The goal was for the toads to catch and eat the beetles that were attacking the sugar cane crops. Not only was this plan unsuccessful (the toads couldn't jump high enough to reach the beetles on the sugar cane stalks), but the cane toad has now become an invasive species. The toads have spread to new areas and have a thriving population. They feed on native animals and the toxin in their bodies often kills their potential predators.
Luckily, previous experiences have taught researchers how to better assess the likelihood that an introduced predator, parasite or pathogen will cause a problem. Nature's behavior can't be completely predicted, however, and scientists never know for certain what will happen when they introduce a plant or animal to an area.
Biological pest control often takes longer to work than chemical pest control and frequently reduces a pest population to a low level rather than eliminating it completely. These facts may be considered a disadvantage by some people. Once a predator population is established, however, biological pest control will operate on its own without the need for further human input (as long as the predator survives).
Biopesticides are produced from or by living things and are considered to be safer for humans than chemical pesticides. There are three types of biopesticides - microbial pesticides, plant-incorporated protectants (or PIPs) and biochemical pesticides.
These pesticides are made from microorganisms, such as bacteria or fungi, which are used to infect and kill pests. Although the microbes are said to form a pesticide, their use is actually an example of biological pest control.
A popular microbial pesticide is the bacterium called Bacillus thuringiensis, also known as Bt. There are different strains of Bt, each producing a different mix of proteins. Some of these proteins kill insect larvae, with different proteins killing different species of insects.
Plant-Incorporated Protectants, or PIPs
PIPs are chemicals made by plants that have been genetically altered in order to produce a particular pesticide. For example, the Bt genes that make pesticide proteins can be inserted into plants. The genes become active and the plants produce their own pesticide, which kills insects that try to eat the plant. The pesticide proteins don't hurt humans.
Biochemical pesticides are non-toxic chemicals made by living creatures. They are usually the only kind of pesticide that organic food producers are allowed to use.
A biochemical pesticide's job is to control a pest, but it may not kill the pest directly. Semiochemicals are chemicals released by living things that influence the behavior of other organisms. A pheromone is a semiochemical that affects a member of the same species as the organism that made the pheromone. Insect pheromones attract other insects, which may be insects of the opposite gender or insects of both genders, depending on the pheromone. Pheromones can be used by farmers to lure insects into a trap.
Pyrethrins are another type of biochemical pesticide. They are made in the seed cases of a type of chrysanthemum and kill insects by damaging their nervous systems. Unlike some chemical pesticides, pyrethrins quickly break down in the environment and are said to be non-residual chemicals. They have low toxicity to humans and other mammals but should still be treated with respect. It's important to realize that just because a chemical is natural doesn't automatically mean that it's completely safe for humans. Still, pyrethrins are considered to be some of the safest chemicals to use as pesticides. However, they are toxic to fish and bees.
A substance called piperonyl butoxide is often added to pyrethrin insecticides. Piperonyl butoxide has no ability to kill insects by itself. However, it makes the insecticidal ability of pyrethrins stronger by stopping an insect's body from breaking down the pyrethrins.
Organic Pest Control
Kitchen Ingredients as Pesticides
There are some common kitchen substances that can be used to get rid of garden pests. For example, a canola oil spray works as an insecticide yet is nontoxic to humans. It shouldn't be sprayed near water, however. Garlic repels birds and insects and also degrades quickly. Black pepper oil is used to repel mammals. Chili peppers are chopped and then soaked in water for a day to make an insecticide. Some people add an small amount of soapy water to the chili water to make a spray that will stick to plants. Try to use a soap or detergent that is safe for the environment if you do this. Be careful if you use chili peppers, since they can burn and irritate skin and mucous membranes. Although it may not be a common household product in some countries, neem seeds and the oil from the seeds can be used to create a natural pesticide that kills many insects.
Using Chemical Pesticides
Types of Chemical Pesticides
Chemical pesticides are synthetic substances that are created to kill or injure pests. They can be classified in several different ways. For example, pesticides may be categorized based on when they begin to work after they are applied to a pest. Contact pesticides kill a pest shortly after touching the surface of its body. Systemic pesticides are absorbed by plants or animals and must spread through the inside of their bodies to untreated areas before they can kill pests. The pesticides may travel through the whole body or just to one particular area in the body.
Pesticides may also be classified according to how they affect pests. Desiccants remove water from the bodies of plants or animals, for example, and defoliants cause plants to drop their leaves. Insect growth regulators kill insect larvae by interfering with the process in which juvenile insects molt and turn into adults. Although most pesticides kill the pests that they attack, not all of them do. Repellents simply repel pests, as their name implies. An example of this type of pesticide is DEET, a common substance in personal insect repellents. Sterilizing agents interfere with the ability of the pest to reproduce, but they don't kill the creature that they affect.
Additional ways to classify pesticides are by the type of organism that they are designed to kill, as the table below shows, or by their chemical structure.
Classifying Pesticides by Target Pest
slugs and snails
acaricides (or miticides)
fleas, ticks and mites
Chemical Pesticides and Human Health
Pesticides are potent chemicals designed to destroy pests. They may harm us, too. This harm is generally reduced because farmers often have to follow strict laws about pesticide use. These laws include rules about allowable pesticide levels on crops and about pesticide storage, transport and application. Despite all the regulations, however, we do ingest pesticides in our foods and drinks, inhale pesticides from the air that we breathe and absorb pesticides through our skin.
The agencies that regulate pesticides usually admit that chemical pesticide use does involve safety risks, but they say that these risks are acceptable considering our need to protect agricultural crops and feed people. Many individuals disagree with the idea that the risk is "acceptable", however. The agencies also claim that most people are exposed to only small amounts of pesticides in their daily lives. However, if a pesticide is very toxic a small amount can be dangerous.
The effects of a pesticide on the human body depend on several factors, including the nature of the pesticide, the amount of chemical involved, the length and frequency of exposure and the age of the person being exposed to the pesticide. Children are especially susceptible to the effects of chemicals because of their small size and the fact that their bodies and nervous systems are still developing.
Symptoms of acute pesticide poisoning develop immediately or shortly after exposure to a dangerous dose of a pesticide. The symptoms may be relatively minor, such as a headache, dizziness, nausea and diarrhea. More serious symptoms include vomiting, abdominal pain, a rapid pulse, lack of muscle coordination, mental confusion, inability to breathe, burns, loss of consciousness and even death.
Other possible effects of pesticide exposure may take longer to develop. It's hard to definitely prove that a pesticide is responsible for a human disease, but certain pesticides are suspected of causing nervous system damage and cancer.
Common Types of Insecticides and Their Dangers
Many pests are insects and so most pesticides are insecticides. Important types of insecticides, which are classified based on their chemical structure, are organophosphates, carbamates, organochlorines, pyrethroids and neonicotinoids.
Organophosphates kill insects by interfering with the activity of their brains and nervous systems. Unfortunately, they can also affect the nervous systems of humans and other animals. They do this by altering a normal process involving acetylcholine, a common neurotransmitter. Neurotransmitters control the transmission of a nerve impulse from one nerve cell to the next. They are normally broken down or removed once they've done their job. Organophosphates interfere with the action of acetylcholinesterase, the enzyme that breaks down acetylcholine.
Carbamates are also used as insecticides and work in a similar way to organophosphates. They break down quicker and are less dangerous to humans, however.
The most famous organochlorine is DDT (Dichlorodiphenyltrichloroethane). It has been banned in several countries for decades, except for very specialized use, but it is a very persistent pesticide. "Persistent" pesticides stay in the environment for a long time and don't break down. DDT is still found in soil and in the bodies of animals and humans. DDT thins the shells of bird eggs, causing the developing babies to die. It also disrupts our endocrine systems (which produce the hormones that we need) and is thought to damage genes and increase the risk of cancer.
Pyrethroids are synthetic chemicals derived from pyrethrins. Like pyrethrins, their use is increasing because they are considered to be less toxic than the other categories of insecticides.
Neonicotinoids are derived from nicotine, a plant chemical. They interfere with a pathway that is common in the insect nervous system and are suspected of playing a role in honeybee colony collapse disorder.
Integrated Pest Management
Due to the concerns about chemical pesticide safety, some communities are now using integrated pest management techniques to control pest problems. Integrated pest management, or IPM, involves the use of multiple techniques to solve a pest problem as safely as possible. These techniques include physical or mechanical methods, such as picking pests off plants, creating barriers to block pests from entering an area, removing clutter and changing the conditions that attract pests. They also include choosing an appropriate garden or field design. Companion plants that protect a desired crop may be grown beside the crop, for example. The soil composition or growing conditions may be changed to discourage pests. Biological pest control methods and biopesticide applications are also used in IPM. Even chemical pesticides are used, if they are absolutely necessary.
The good news is that public pressure and human health concerns are stimulating some communities and individuals to use safer methods to manage pests. These methods include physical control, biological control, the use of biopesticides, and, if necessary, the use of safer chemical pesticides. Some local governments have even stopped using pesticides on ornamental plants and lawns for purely cosmetic reasons. In addition, some people are now willing to accept fruit that hasn't been treated with chemical pesticides and looks less than perfect, provided it's safe to eat.
© 2012 Linda Crampton
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