**1. Introduction**

Insecticides are toxic substances that are used to kill or control insects. Insects pests affect humans directly by transmitting diseases or indirectly by attacking cultivated plants in farms or in storage, thus affecting food security. It is documented that the use of insecticides by man dates as far back as 1000 B.C, or earlier when burning of stone containing sulfur (brimstone) was used as a fumigant.

Substances used to kill or control insect pests can also be referred to as pesticides, though the latter word has a wider scope of application, since other non-insect pests also exist.. Insecticides in wide use are mostly synthesized organic compounds, though there are some organic compounds of plant origin referred to as "botanicals", in addition to inorganic compounds of natural and synthetic origin. Certain insecticides of synthetic, or‐ ganic or inorganic origin function as insect repellents, causing little or no harm at all to the target insects. In most situations insecticides are applied by spraying or dusting onto plants and other surfaces traversed or fed upon by insects. However insecticides/pesti‐ cides of chemical origin can affect human health directly or indirectly by disrupting eco‐ logical systems that exist in rivers, lakes, oceans, streams, wetlands, forests and fields. Release of chemicals into the environment can have global impacts and there is therefore need to use safer analogues designed with safety in mind. A review of some "safe" in‐ secticides used in Africa is presented.

Pesticides in general are toxic chemicals which adversely affect human health when mishan‐ dled. Their effects may be direct, for example, during application or when consumed in sui‐ cide bids. Also their effects may be indirect when the environment is contaminated either

© 2013 Kareru et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Kareru et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

due to non-specificity of the target or when higher dosages are used either accidentally or due to ignorance. Such pitfalls may be overcome by use of "smart insecticides". The latter may be designed by incorporating a delivery system so as to release an insecticide over an extended time at a controlled rate. Such insecticides, therefore, target the intended pests without adversely affecting the human health or the environment.

specificity towards different insects (Santie et al, 2011). Bt bacterium contains insecticidal protein crystal that is eaten by insects. The crystal then dissolves in the midgut of the insect. The toxin mixture is released and the proteins are cleaved into active forms. The toxins bind to the midgut cells, assembling a pore that leads to disintegration of the cells, gut paralysis and death. The Bt strains are known to have toxins specific for insects such as caterpillars, beetles, flies and mosquitoes and have little or no effect on mammals. South Africa has been reported to grow more than 85% of the countries cotton and some maize and is the only Af‐ rican country reported so far to grow 67% of the country's total maize production for food (James, 2007) using the Bt insecticides technology. Outside of South Africa, only Burkina Fa‐ so and Egypt allow commercial cultivation of GM crops. Accessibility of these products is, however, relatively restricted, especially in developing countries such as in Africa, due to vocal opposition to GM technology and lack of regulatory mechanisms to deploy such tech‐ nology (Sentie and David, 2011). South African farmers and consumers have already shown a willingness to embrace biotechnology (cotton, maize, and soybean) resulting in improved yield or reduced cost, however, the Bt potato would be the first publicly-funded bioengi‐ neered crop to be released in Africa. Some commercially available Bt varieties and target pests include: *Bacillus thuringiensis*, var. *tenebrionis*- for control of Colorado potato beetle and elm leaf beetle larvae; var. *kurstaki* - for caterpillars; var. *israelensis* – for mosquito, black fly, and fungus gnat larvae; var. *aizawai* for wax moth larvae and various caterpillars, especially

Use of Botanicals and Safer Insecticides Designed in Controlling Insects: The African Case

http://dx.doi.org/10.5772/53924

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Plant extracts are commonly referred to as plant botanicals and are the secondary plant me‐ tabolites synthesized by the plant for protective purposes. Some of these compounds are toxic to insects. These plant compounds are called botanical pesticides, plant pesticides or simply botanicals. Many of the plant botanicals are used as insecticides both in homes, in commercial as well as in subsistence agriculture by small-scale farmers (Table 1). They may be contact, respiratory or stomach poisons. Botanicals are not very selective because they

Plant insecticides act in several ways: as repellents by driving the insects away due to smell or taste, as antifeedants which cause insects on the plants to reduce their food intake and hence starve them to death; as oviposition deterrents, by preventing insects from laying egg;

Plant insecticides have several advantages. Among them are short life spans once applied and are not poisonous to humans and livestock. Secondly, botanicals do not harm the natu‐ ral enemies of the pests, such as the lady bird beetle. They are cheap, easy to prepare and in most cases readily available and have more than one active ingredient which work synergis‐ tically making it difficult for pests to develop resistance. Figures 1-5 shows some structures

the diamondback moth caterpillar.

target a broad range of insect pests.

**3. Synthesis of pesticides from plant botanicals**

or as inhibitors by interfering with the life cycle of the insects.

of some compounds from some of the plants used.

One of the novel techniques in recent use is to encapsulate the insecticides within a macro‐ molecular network. Biopolymers have in recent times been used for this purpose. For exam‐ ple, hydrogels of natural polymers such as sodium alignate, starch, gelatin, carboxymethyl cellulose etc, have been used for encapsulation of insecticides (Anamika et al, 2008).

The future development and use of safer pesticides in Africa will need to address safety con‐ cerns using functionalized polymers as delivery systems. Such technology will increase the efficiency of insecticides by targeting the specific pests while indirectly protecting the envi‐ ronment by reducing pollution and safety to end users. This will impact positively on health by controlling disease causing vectors and food security as well.
