Plant extracts have been used as biological pesticides for many decades. The first botanical or natural insecticides was used in the period of 17th century, when it was shown that nicotine was extracted from tobacco leaves, killed plum beetles.
One of the most important global problems is protecting crops from insects. For the control of insects, synthetic chemicals are continuously used and their toxicity endangers health of human, animals and food consumers. The negative effects on human health led to a resurgence of interest in botanical insecticides due to their minimal costs and ecological side effects.
Botanical insecticides are naturally occurring chemicals (insect toxins) extracted or derived from plants or minerals. They are also called natural insecticides. Synthetic fertilizers and pesticides can be harmful to the ecosystem. Therefore, natural or botanical insecticides always should be preferred to synthetic ones. Natural or botanical insecticides can be homemade.
In this review, biological control of insects in crop production using botanical products will be focused. An overview of botanical insecticides from the chemical point of view and classify their effects on insects will be provided.
Botanical insecticides are natural chemicals extracted from plants with insecticidal properties and used as an excellent alternative to synthetic or chemical pesticides for crop protection to avoid negative or side effects of synthetic insecticides.
Botanical insecticides can be of different types. Neem oil is one such insecticide that has been used through the centuries. Some other insecticides are used like sabadilla and rotenone etc. Although there are many more natural pesticides available such as BT (a soil microbe toxic to certain insects), milky spore (also a microbe), nicotine (extracted as a tea from bulk tobacco), pyrethrum (derived from a variety of daisy), and iron phosphate (a natural mineral toxic to slugs and snails).
Why prefer natural insecticides
The market is flooded with all sorts of insecticides, pesticides and other pathogen-killing chemical formulations. Many of these products are effective in getting rid of troublesome insects within a short time. However, the problem is increased risk of bioaccumulation, which over time affects the food chain and reaches humans. Considering this factor, most gardeners prefer planting natural insect repellents for pest control.
Why and how to make natural insecticides at home
In addition to polluting the environment and disturbing the food chain, a worrying issue with repeated use of the same insecticide over a period of time, is development of resistance power by household insects. Consequently, to reduce these negative outcomes, a perfect solution can be prepared. These solutions can be made at domestic level without any problem. These are following botanical or natural insecticides and question is raised how it can make?? It will be discussed below;
To make garlic spray
Garlic is well-known for its pungent aroma. Chop garlic cloves (3 ounces) and soak the pieces in mineral oil (2 tablespoons) for one night. For added effectiveness, stir in fish emulsion (1 teaspoon) in the garlic mixture.
Tomato leaf as spray
Leaves of a mature tomato plant, 4 pints water, and 1 teaspoon cornstarch. First, blend the tomato leaves in a mixer and stir the extract with cornstarch and water. Using a sprayer, apply this mixture to rose and other flowering plants.
Neem oil spray
Neem oil is extracted from the seeds of neem trees. This oil has a pungent smell. So this oil can be used as an insecticide due to its bad smell. Neem oil has to be diluted with water before it is applied on plants. It can control insects like white fly, aphids and Japanese beetles. Neem oil is also used an excellent miticide as well as a fungicide.
The best natural insecticide is salt water. Dissolve 4 tablespoons salt in 2 gallons of water. Apply this saline solution to kill the garden pests like spider mites and cabbage worms.
Chile pepper insecticide spray
Similar to garlic spray, mix 1 tablespoon of chile powder with 1 quart of water and several drops of mild liquid soap. This mixture can be used full-strength on the leaves of affected plants.
Diatomaceous earth as a natural pesticide
This natural substance is made from a sedimentary rock created by fossilized algae (diatoms) and which is a rather abundant resource (diatomaceous earth is said to make up 26% of the earth’s crust by weight). Diatomaceous earth has a number of uses in and around the home and acting as a natural insecticide is just one of them.
Soap spray insecticide
Similar to the oil spray, To make basic soap spray insecticide, mix 1, 1/2 teaspoons of a mild liquid soap (such as castile soap) with 1 quart of water, and spray the mixture directly on the infected surfaces of the plants. It can control mites, aphids, whiteflies, beetles, and other hungry little insects.
Pure nicotine is toxic to animals as well as humans hence it is best used in diluted form. You may also prepare a homemade natural insecticides with nicotine, by boiling around 100 cigarettes in four liters of water. Keep the water overnight and strain it before storing. You have to mix one part of this mixture with two parts of water before spraying it on plants.
Sabadilla is produced from the seeds of a plant that has resemblance lilies in look. The active ingredient in sabadilla is an alkaloid called veratrine. It is highly toxic to insects which come into contact with this insecticide or ingest it. Precautions should be necessary to use this insecticide owing to its dust form.
Pyrethrin and Rotenone
Pyrethrin is obtained from Dalmatian chrysanthemum and Rotenone is derived from the roots of plants that belong to the genus Derris. . It has been observed that small amount of this insecticide may not be toxic to insects but still may repel them.
The insecticidal properties are contained in the stems and roots of Ryania speciosa (a South American shrub). It controls important lepidopteran larval pests at 3 to 16 g alkaloid equivalents per acre, making it one of the most potent natural product insecticides. Although, it acts as a stomach poison.
Sources of natural insecticides
The most common plants having potential to be used as a source of bio-pesticides include Neem (Azadirachta indica), Sweet flag (Acorus calamus), Clove (Syzygium aromaticum), Delphinium (Delphinium denudatum), Walnut, Keekar (Acaccia nilotica), Aak (Calotropis procera) and Safaiyda (Eucalyptus camaldulensis) etc. One such plant based bio-pesticide has been prepared by the International Centre for Chemical and Biological Sciences (ICCBS), University of Karachi (KU) and has been marketed.
Effectiveness of natural insecticides
Some botanical pesticides are toxic cause death to stored product insects (Padin et al., 2013). Neem oil at 2% and neem seed water extract at 3% significantly reduced the whitefly, jassids and thrips infestation up to 12 days after spray as compared to that in the control (Rashid et al., 2012). Neem derivatives kill small bodied insects and immature stages of several insect species. Neem oil extract at 0.04% caused 100% kill of the 1st and last larval instar of mosquitoes in 24h (Attri and Prasad, 1980).
It has been reported that plant parts, oil, extracts and powder mixed with grain reduced insect oviposition, egg hatchability, postembryonic, and progeny development (Asawalam & Adesiyan, 2001; Shaalan et al., 2005). Essential oils possess acute contact and fumigant toxicity to insects (Abdelgaleil et al., 2009).
Several essential oil components act on the octopaminergic system of insects. Octopamine is a neurotransmitter, neurohormone, and circulating neurohormone-neuromodulator, and its disruption results in total breakdown of the nervous system (Hollingworth et al., 1984).
Advantages of natural insecticides
Reduction of health hazards in comparison to the application of conventional pesticides. They are effective in very small quantities and often decompose quickly. So there is no disaster of transferring the residues in food chain. Botanical pesticides are less expensive and easily available because of their natural occurrence especially in oriental countries.
Reports on negative effects of synthetic pesticides and environmental risks resulting from their indiscriminate application have renewed interest towards botanical pesticides as an Eco chemical approach in pest management. Natural plant chemicals will play a significant role in the future for pest control in both industrialized and developing countries.