Insecticides have increased agricultural productivity since the last century. Prior to this, farmers employed the use of chemicals like sulfur, arsenic and led to get rid of insects on farmlands.
Insecticides have the potential to damage ecosystems. Extensive use of insecticides has been associated with many problems. Although they may kill target insects, they are also capable of killing useful insects like bees.
Insects can, over time, develop resistance to insecticides. They are also toxic to humans and animals –hence, their use has been strictly regulated, although this is not so in developing countries.
Insecticides are classified into two groups. These are;
- Contact insecticides which have no residual activity and are not persistent
- Systemic insecticides which are persistent and have long term activity.
Insecticides can also be classified as;
- Natural insecticides such as neem and nicotine made by plants as a defense against insects.
- Organic insecticides such as organochlorides, organophosphates, carbamides, and pyrethroids
- Inorganic insecticides made from metals
Some insecticides work by damaging the nervous system, while others work by damaging their exoskeletons, or drive them away. They can be packaged in various forms like sprays, dusts, gels, and baits.
Uses of Insecticides
- Insecticides are used to control and kill insects and arthropods that may damage agricultural produce.
- They are also useful for controlling and killing vectors of diseases like mosquitoes that may affect human life.
Dangers of Insecticides
One of the major problems of using insecticides is environmental contamination and the eventual development of resistant insect species. Insects are toxic substances that could affect not just the target insect species but also useful insects.
Bioaccumulation of certain insecticides in the environment can pose a serious danger to both humans and wildlife. Although many insecticides are short-lived in the environment, some remain persistent and are ingested by animals, mainly when applied in large amounts.
Insecticides may leach through the soil and affect groundwater –thus contaminating it. Suspended particulates matter from sprayed insecticide application may pass off as drift, pollute the air, and affects air quality. This could cause eye and skin irritation in humans.
DDT, dieldrin, and aldrin are chlorinated hydrocarbons that could easily contaminate the soil. Through the repeated application, these chemicals can accumulate in the soil in large amounts, affecting wildlife and increasing up the food chain.
They persist in the fatty tissues of animals as they go up the food chain, and showing toxic effects later. Birds of prey such as hawks, eagles, and falcons are the most affected.
The declining populations of these birds have been traced to the hazardous effects of DDT and its related chemicals. It is for this reason that these chemicals have been restricted and eventually banned in many countries.
There have been reported cases of human poisoning by insecticides. In fact, the use of parathion, one of the most common organophosphates in the United States, was reduced owing to its toxic effects on farm laborers who came in direct contact with it.
Additionally, the tendency for target insect species to develop resistance to insecticides is another major problem.
These resistance populations survive insecticide application and multiply, eventually forming the majority of the insect population. Resistance means an insect population is no longer susceptible to the effects of insecticides.
Insecticides also encourage the growth of harmful insect species by killing off natural insect predators of insects.
For example, ladybirds, wasps, and beetles are the natural enemies of aphids –an insect pest of food crops. Insecticide application eliminates these natural predators and encourages the growth of aphid populations.
Integrated Pest Management
Due to the problems associated with the intensive use of some chemical insecticides, the current practice of insect-control combines their use with biological methods in an approach known as integrated control.
This approach combines minimal use of insecticide by the following ways:
- The use of pest-resistant crop varieties.
- The use of crop-raising methods that inhibit the growth of insect pest populations.
- The disruption of the pest’s reproductive cycle by the release of sterilized pests.
- The release of natural predators or parasites of the pest species.