**1. Introduction**

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Insects are one of the biggest animal populations with a very successful evolutive history, once they can be found chiefly in all possible environments all over the world, and the num‐ ber of species and individuals. Their success can be attributed to several important evolu‐ tionary aspects like wings, malleable exoskeleton, high reproductive potential, habits diversification, desiccation-resistant eggs and metamorphosis, just to name a few. Some spe‐ cies are especially valuable for humans due to their ability in providing several important goods, such as honey, dyes, lac and silk. On the other hand, many insects are vectors of many diseases, and many others damages crop plantations or wood structures, causing seri‐ ous health and economic issues.

Among all identified insects, over 500,000 species feed on green leaves. About 75% of them have a restrict diet, eating only a limited range of species, sometimes being even specie spe‐ cific [1]. This kind of insect brings major concern to the agriculture. Their high selectivity im‐ plies in a closer insect attack on crops. It is estimated that about 10,000 insect species are plagues and, compromising the food production, either in the field or after the harvest [2]. It was estimated that somewhere around 14-25% of total agriculture production is lost to pests yet [3].

Agriculture is one of the main pillars of human population increase over the last millenni‐ ums, providing mankind with several important commodities such as food, fuel, healthcare and wood. This huge production should feed 7 billion people, and also generate several in‐ puts for many industrial processes and commercial applications. In order to combat the nu‐

© 2013 Perlatti 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 Perlatti 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.

merous losses that are caused by insects on agriculture, several chemicals have been used to kill them or inhibit their reproduction and feeding habits. Those classes of compounds are collectivity known as insecticides. These molecules are able to interfere in the insect metabo‐ lism. They alter is in such a way that the plague cannot feeds on the crop or the harvest or even reproduce anymore. The use of insecticides is described since ancient times, with docu‐ ments providing evidences as far as in the 16th century BC. The *Ebers Papyrus*, wrote by the Egyptians, reports several chemical and organic substances used against overcome fleas, gnats and biting flies among others [4]. Nowadays, the insecticides are widely employed around the world. Several known substances are extremely effective in controlling or even wiping out almost all important agricultural plagues. This multi-billion-dollar has an esti‐ mated production of 2 million metric tons of hundreds of chemical and biological different products, with a budget of a US\$35 billion dollars worldwide [5].

crops and their efficacy and availability improvement and reduction of environmental con‐ tamination and workers exposure [8]. In that line, new types of formulation were devel‐ oped. One of the most promising is the use of micro and nanotechnology to promote a more

Polymeric Nanoparticle-Based Insecticides: A Controlled Release Purpose for Agrochemicals

http://dx.doi.org/10.5772/53355

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Casanova *et al*. [9] evaluated the production of a nicotine carboxylate nanoemulsion using a series of fatty acids (C10 – C18) and surfactant. The oil-in-water nanoemulsion showed a monomodal distribution of size, with mean particle sizes of 100nm. The bioactivity of the insecticide formulations was evaluated against adults of *Drosophila melanogaster* by assessing the lethal time 50 (LT50). They observed that the encapsulation efficiency decreased with in‐ creasing size of the fatty acids tested. The bioactivity followed the same trend, with better bioactivity when the chain length decreased. This would be readily attributed to the higher amount of active compound inside the nanoemulsion. For the smallest fatty acid emulsion used, the capric acid (C10) one, the greatest encapsulation efficiency was observed, but it had the lowest bioactivity. The results were explained in terms of lesser bioavailability of the insecticide in its active form due to increased stability of the organic salt formed between the insecticide and the fatty acid. This experiment highlights the necessity of developing differ‐ ent kinds of possible assembles between the active compounds and matrix, and extensively studying the interactions in nanoscale formulations, where sometimes nontrivial effects

Wang *et al.*[10] developed an assemble of oil-in-water nanoemulsion (O/W) with 30 nm droplets by careful control of experiment conditions, using the neutral surfactant poly(oxy‐ ethylene) lauryl ether and methyl decanoate to encapsulate highly insoluble β-cypermeth‐ rin. The dissolution of the insecticide was enhanced. The stability tests were performed by spraying nanoemulsion in a glass slide and observing under polarizing light microscopy. They showed no apparent precipitate in nanoemulsions samples. These results were differ‐ ent from the ones obtained using a commercial β-cypermethrin formulation, with apparent signs of solid residues after 24 hours. This enhanced stability may be used to decrease the concentration of insecticides in commercial spray applications, without losing efficiency.

Allan *et al.* [11] published the first report on a controlled release system of an insecticide through a polymeric encapsulation. Even so, at first the encapsulated systems were not so effective. Problems associated with controlled release and particle stability hindered their practical field application for some decades. In one of the first successful works in the field of pesticides encapsulation, Greene *et al.* [12] used poly (n-alkyl acrylates) (Intelimer®) to produce temperature-sensitive microcapsules of the organophosphate insecticide diazinon.. The active chemical was controlled release by increasing the ambient temperature above

efficient assembly of the active compound in a matrix.

**2.1. Nanoemulsions**

might be unexpectedly observed.

**2.2. Classical micro and nanoparticles**

**2. Application of insecticides nanoformulations**

Insecticides are used in different ways, based on the physical-chemical characteristics of the each chemical substance, the area that needs to be covered and the target. Typical applica‐ tion of insecticides in crops is made by spraying a solution, emulsion or colloidal suspension containing the active chemical compound, which is made by a vehicle which may be a hand pump, a tractor or even a plane. This mixture is prepared using a liquid as a carrier, usually water, to ensure a homogenous distribution. Other methods for applying insecticides are through foggers or granule baits embedded with the active compound, among others that are less used. However, due to several degradation processes, such as leaching or destruc‐ tion by light, temperature, microorganism or even water (hydrolysis), only a small amount of these chemical products reaches the target site. In this case, the applied concentrations of these compounds have been much higher than the required. On the other hand, the concen‐ tration that reaches its target might be lower than the minimum effective one. In general, de‐ pending of the weather and method of application, the amount of applied agrochemicals, as much as 90%, may not reach the target and so do not produce the desired biological re‐ sponse. For this reason, repeated application of pesticides become hence necessary to effi‐ cient control of target plagues, which increase the cost and might cause undesirable and serious consequences to the ecosystems, affecting human health [6]. Due to the lack of selec‐ tivity, their unrestrained use can also lead to the elimination of the natural enemies, what implies in the fast growth of plague population. Moreover, it often makes the insects resist‐ ant to the pesticides.

Another important point that needs attention is the formulation for the application of the in‐ secticide on the crops. There are several different classes of compounds, which sometimes do not match with a simple dilution in water and must be prepared by other means such as powders, emulsions or suspensions. Some kinds of formulations must be handled with more precaution, since it can severely contaminate workers on the field with small airborne solid particles that can be inhaled [7].

The advances in science and technology in the last decades were made in several areas of insecticide usage. It includes either the development of more effective and non-persistent pesticides and new ways of application, which includes controlled release formulations (CRFs). The endeavors are direct towards the successful application of those compounds on crops and their efficacy and availability improvement and reduction of environmental con‐ tamination and workers exposure [8]. In that line, new types of formulation were devel‐ oped. One of the most promising is the use of micro and nanotechnology to promote a more efficient assembly of the active compound in a matrix.
