layered silicate nanocomposites as matrix for bioinsecticide formulations

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Polymer/layered silicate nanocomposites as matrix for bioinsecticide formulations

6

Prabhakar Mishra*, R. Seenivasan†, Amitava Mukherjee†, Natarajan Chandrasekaran† Department of Biotechnology, School of Applied Sciences, REVA University, Bangalore, Karnataka, India* Centre for Nanobiotechnology, VIT, Vellore, Tamil Nadu, India†

6.1 ­Introduction Ecological food production for a hastily growing human population is one of the foremost challenges to be tackled by the agriculture sector worldwide (Godfray and Garnett, 2014; McClung, 2014). Therefore, the augmented use of fertilizers and pesticides has become indispensable to maximizing agricultural efficiency. Despite their benign role in agriculture, pesticides have become perilous to the ecosystem because of their toxicity, the amount of pollution, and the exposure duration (Kohler and Triebskorn, 2013). Approximately 2.5 million tons of insecticides are used on crops annually (FAO, 2012; Fenner et al., 2013). While the intermittent application of these pesticidal compounds increases the risk of pest resistance and its hazardous influence on the quality of food, their improper usage and misapplication leads to the generation of extensive waste compounds that add to the cost while unfavorably affecting the ecosystem and human health (Abhilash and Singh, 2009; Kohler and Triebskorn, 2013). Furthermore, it has been projected that as much as 90% of the pragmatic pesticides are being misplaced into the air during the application stage itself as well as in the form of run-off to water bodies, which affects the ecosystem and usage costs of the farmers (Ghormade et  al., 2011; Stephenson, 2003). Therefore, it becomes essential to have safe and efficient pesticide usage strategies that will help to reduce the adverse effects of pesticide applications. In view of these facts, nanotechnology offers a propitious role and can be applied as a revolutionary tool for the delivery of these agrochemicals in a safer manner (Ghormade et al., 2011; Gonzalez et al., 2014). Additionally, technical developments over the years have led toward developing transport systems that could reduce the pesticide load (Ghormade et al., 2011). Recently, there has been exponential growth toward the development of nano-sized materials that feature differently in comparison to the use of their bulky counterparts. These nanometric systems have an extensive range of applications, including healthcare to cosmetics as well as agricultural or environmental-based usage (Bakshi et al., 2014; Ma et al., 2013; Srivastava et al., 2011). In the agricultural sector, these Nano-Biopesticides Today and Future Perspectives. https://doi.org/10.1016/B978-0-12-815829-6.00006-1 © 2019 Elsevier Inc. All rights reserved.

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systems are applied to obtain the controlled release of active components for pest management as well as nutrients (Ghormade et  al., 2011; Gonzalez et  al., 2014). Nanosensors are also used as nanotechnology tools to monitor environmental conditions and impacts (Ghormade et al., 2011; Nair et al., 2010). The applicative role of these nanometric systems in the form of vector systems for a convenient delivery of pesticidal compounds is well known (Kah et al., 2013; Kah and Hofmann, 2014). According to Sasson et al. (2012), the merits of nanosized formulations are: • Improvisation in its efficiency owing to larger surface area. • Upsurge in systemic property due to nanosize and advanced mobility. • Reduction in residual toxicity to the abolition of organic solvents used conventionally for various pesticides and their formulations. This chapter considers the advancement of nanotechnology-based vector systems for bio-derived insecticides. The foremost biocidal agents that have been applied are well defined, together with their advantages over their bulk counterparts and their foremost efficiency. Therefore, the following discussion will point to the propitious role of bio-based insecticides and their enhanced efficacy upon encapsulation with various bio-based polymers.

6.2 ­ Conventional Pesticides and Residual Pollution Diverse varieties of conventional pesticides are being applied to control pests in general. These pesticides are organochlorines, nicotinoids, organophosphates, pyrethroids, rotenoids, and carbamates, which are mostly neurotoxins like acetylcholine esterase inhibitors (USEPA, 1999). Pyrethroids, however, originate from naturally occurring pyrethrins that were obtained from the flowers of the pyrethrum plants used widely for household pests (Davies et al., 2007). Although these pesticides possesses efficacy against the various pest species, they tend to have a few major demerits such as their inappropriate and uncontrolled application, which eventually results in ecoresidual pollution problems. The irregular usage of conventional pesticides has resulted in increased ecotoxicity and resistance. In fact, indiscriminate use of pesticides induce resistance in target pests via amplification of the structural genes encoding the detoxifying enzymes. Norris and Norris (2011) described elevation in resistance among pests against pyrethroids, DDT, and malathion-treated net materials. Also, the upregulation of certain enzyme activities such as GST (glutathione S-transferases) and α and β-esterases depicts the metabolic detoxification of the enzymes inside the insect body, which confirms the insecticide resistance. Similarly, the resistance in the wild populations of insect vectors such as C. quinquefasciatus against the carbamate and other group of pesticides has forecasted the ineffectiveness of the insecticide residual spray (IRS) and other vector-controlling strategies (Yadouléton et al., 2015). Strode et al. (2012) has discussed the increased resistance toward organophosphates in the major pest ­species.

6.3 ­ Bio-derived insecticides

Various mechanisms can work independently or in a reciprocal manner like the resistance occurring through disturbances in the metabolic pathway and overexpression of the decontaminating enzymes or the alterations in the amino-acid sequences, which results in the irregular metabolic activities. Temephos, an organophosphosphate, is a widely applied larvicide throughout the world for larval control (Braga and Valle, 2007; Flores et  al., 2006; Jirakanjanakit et  al., 2007; Rodríguez et  al., 2002; Tikar et al., 2009); this induces resistance in several pest species. The residual fragments of these pesticides heap up in the atmosphere, which later distresses the quality of air to breathe. This variety of pollution leads to disorders and infections throughout the world in the form of numerous airborne diseases. A similar condition prevails in various water bodies. Also, the extensive residual part getting splashed away from agricultural fields gets amassed in the hydrosphere, creating the problem of ecotoxicity. This successively becomes lethal for other nontarget living systems prevailing in the water ecosystem. This kind of residual pollution arises due to improper application of these conventional lethal pesticides, which affects the soil ecosystem and causes harmful impacts on nontarget species that are predominant in the pest-prone ecosystems (Topp et al., 1997; Simon-Sylvestre and Fournier, 1980). Likewise, the nutritive value of essential crops deteriorates due to the heavy accumulation of these hazardous chemicals in the soil system. The elevated ecotoxicity problems due to the application of these pesticides in the environment demand a diverse approach for pest control with better effectiveness and target-based materials with better ecobenign value. In this context, the approach of nanotechnological tools to extemporize the condition of pesticidal usage in day-to-day situations can become an imperative step toward decreasing ecotoxicity.

6.3 ­Bio-Derived Insecticides It is well known that secondary metabolites are responsible for self-defense of plants against pests (Menezes, 2005). Some of the common metabolites from plants include terpenoids, phenolics, and alkaloids. These compounds, which are present all through the plant or are confined in certain tissues, can be attained via extraction with the help of various organic solvents or through the application of steam distillation (Castro et al., 2005; Dietrich et al., 2013). The mechanism of action for these metabolites may vary, particularly when the action is due to the multifaceted combination of compounds that can be noxious or nauseating to the target organisms, leading to developmental variations including the reduction in the growth, behavioral changes and sterility (Isman, 2000; Koul, 2012; Koul and Walia, 2009; Menezes, 2005). There are different varieties of biopesticides that, upon transformation to the nanometric size, become more effective against dreadful pest species. The applicative strategies of these bio-derived insecticides toward the control of pests and insects is not new; these biopesticides were applied more than 4000 years ago in Asian and African countries for the control of dreadful pests and insects (Venzon, 2010). These natural insecticides contain biological, chemical, and mineral

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materials, among which a few products are commercially available such as neem, garlic, cinnamon, pepper, essential oil products, pyrethrum, abamectin, and Bacillus thuringiensis (Bt) (De Bach and Rosen, 1991; Dybas, 1989; Koul, 2016; Koul et al., 2008; Lacey et al., 2001; Nielsen, 1990; Salgado et al., 1998). Azadirachtin is the major bio-based insecticidal compound isolated from neem, Azadirachta indica seeds (Nisbet, 2000). It has multiple types of effects against a variety of pests (Koul and Wahab, 2004). The efficacy is due to limonoids present in the seeds and azadirachtin is a major active ingredient responsible for the antipest activity. There are also several other limonoids that have growth inhibitory and antifeedant activities against a variety of pests (Boursier et al., 2011; Cepeda-Palacios et al., 2014; Koul, 2012). According to Mordue (2004), azadirachtin has more than one mode of action as it prevents the formation of new assemblages of organelles, blocks the transport and release of neurosecretory peptides, and inhibits protein synthesis. It may also prevent the transcription and translation of proteins expressed during various stages of the lifecycle. Other than neem, there are several other plant species that have the potential to control insects and other pests (Burt, 2004; Choi et  al., 2009; Garg and Singh, 2011; Gomes et al., 2014; Koul, 2016; Wattanasatcha et al., 2012); a few of them are shown in Table 6.1. Similarly, during the last decade several essential oils have shown significant potential to control pests (Koul et al., 2008; Kim and Lee, 2014).

Table 6.1  Various Bio-Based Pesticides and Their Carrier Polymer Matrices Bio-Based Pesticide

Chemical Structure and Source

Polymer Carrier Matrices

Azadirachtin

C35H44O16 Neem oil C10H12O2 Clove, cinnamon, ṁyrrh essential oils C10H14O Thyme and peppermint oil C21H20O6 Turmeric

Sodium alginate, starch, chitosan Solid lipid nanoparticles, chitosan Polymer nanoparticles, film of nanoclay Hydroxypropyl cellulose Zein nanoparticles Nanoparticles of chitosan chitosan/βcyclodextrin Chitosan, sodium alginate Poly ethylene glycol Chitosan and locust bean gum

Eugenol

Thymol

Curcumin

Carvacrol

Allyl methyl trisulfide Limonene

C₆H₃CH₃ Essential oil of oregano and thyme C4H8S₃ Garlic oil C10H16O Citrus fruits and lemon grass oil

References Jerobin et al. (2012) Feng and Peng (2012) Garg and Singh (2011) Woranuch and Yoksan (2013) Lim et al. (2010) Zhang et al. (2014) Gomez-Estaca et al. (2012) Bielska et al. (2013) Keawchaoon and Yoksan (2011) Higueras et al. (2013) Yang et al. (2009)

Aloui et al. (2014)

6.4 ­ Nanotechnological tools and bio-derived pesticides

However, the decreased physiochemical stability of these extracts and oils as they are biologically derived makes their strategic delivery difficult. Therefore, the application of nanotechnological methods becomes more imperative to provide stability through evolving various novel formulations and systems that can enhance the efficacy and make them arrive at target sites in a more stable form (Khot et al., 2012).

6.4 ­Nanotechnological Tools and Bio-Derived Pesticides As suggested by Tramon (2014), in comparison to conventional pesticides, the botanical pesticides must be meticulously standardized to a state that can ensure the level of effectiveness as well as greater stability that can make them a propitious tool to compete with their bulk and other synthetic compounds (Isman, 2006; Tramon, 2014). A well-deliberated and steady release system may augment the target specificity and mode of action while also minimizing the impact of residual pollution. Therefore, nanobiotechnology provides a direction toward advancement in the effectiveness and stability of these pesticides (Ghormade et al., 2011; Perlatti et al., 2013). They offer the capability to release the active component to the target as well as a meticulous release of the active molecules at the site of interest. This also would potentially minimize toxic effects toward the nontarget species as well as result in improvisation of their physicochemical stability and prevent early degradation (Durán and Marcato, 2013). Moreover, the vector that can act as a carrier system can be modified to have the controlled diffusion rate, swelling rate, and release kinetics of the active compound (Arifin et al., 2006; Tramon, 2014), which will further depend on the type of mass transfer system applied. There are various nanometric-based pesticides being fabricated through the application of nanotechnology with varied mechanistic approaches that could make an effective measure in any integrated pest management module (Fig. 6.1). These nanotechnology-based techniques provide versatile fabrication approaches for nanometric formulation using the potential biopesticides or bioemulsifiers. Pyrethroids are good examples of this, including nanopermethrin and nanodeltamethrin that provide potential bases for the development of nanoproducts based on botanical insecticides. The nanopermethrin fabrication has been achieved using the solvent evaporation technique (Anjali et al., 2010). This method comprises the micrometric emulsification of the pesticide’s active ingredient, that is, permethrin. It is further subjected to lyophilization, which results in the formation of nanometric permethrin powder. The prepared nanometric formulation attains an amorphous nature, which defines its good activity. The nanometric permethrin, therefore, is a good example of nanoinsecticides having a mean particle diameter of 165 ± 0.9 nm. In fact, the bio-based emulsifiers such as soybean lecithin and ammonium glycyrrhizinate used for the nanometric fabrication make this a potential formulation with a minimum pesticide load. This strategy leads to a reduction in the environmental residual toxicity, which makes this formulation favorable for insecticidal usage (Kumar et al., 2013; Mishra et  al., 2017). Similarly, the nanodeltamethrin formulation has been

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Synapse

Ecdysone activity

Types of encapsulated nano-insectides and its effective targets

Mechanistic approach of nanopesticides toward cell permeability and target delivery

Insect mortality

Hindrance in juvenile hormonal metabolism

fe H ed in in dr g an m c ec e ha in ni sm Feeding deterrent

FIG. 6.1 Various verities of bio-based encapsulated pesticides with a potent mechanistic approach toward pest control.

CHAPTER 6  Silicate nanocomposite matrix for bioinsecticides

in e ion nc ss ra smi d n n Hi tra o ur e n

6.5 ­ Neem-based nanocomposites

p­ repared from an aqua-dispersive nano-sized colloidal formulation of deltamethrin from its aqua-immiscible parental form (Balaji et  al., 2017). The mean hydrodynamic size of the encapsulated droplets achieved was 30.6 ± 4.6 nm. This nanometric pesticidal compound exhibited a greater efficacy toward the target pests, that is, Culex tritaeniorhynchus and Culex quinquefasciatus. Being a propitious insecticide for pest control, it also exhibited its biosafe feature against nontarget species. Taking a cue from this, neem-derived polymer composites have been developed.

6.5 ­Neem-Based Nanocomposites A recent example is a nanopesticidal formulation from azadirachtin (an active insecticidal compound from neem) that is called neem-laced urea nanoemulsion (NUNE). The NUNE fabrication was achieved through the microfluidization process. This process is a high-energy emulsification technique. The nanometric emulsion is an assortment of neem and urea with a mean droplet diameter of 19.3 ± 1.34 nm. The outstanding stability displayed by this nano-sized emulsion aided its mosquitocidal applications against different mosquito species. This kind of pesticidal formulation in a nanometric size delivers its significant toxicity as a propitious insecticidal compound and simultaneously depicts its biobenign property toward nontarget species that are predominant in the pest-prone ecosystems. The neem portion of this nanometric pesticidal formulation helps in controlling pests while the urea portion helps in maintaining its ecosafe property by providing fertility to the ecosystem (Mishra et al., 2018). Riyajan and Sakdapipanich (2009) formulated capsules using Na-Alginate coated with glutaraldehyde and natural rubber, which was later evaluated for the release of azadirachtin. The encapsulation efficacy was found to be greater than 90%, and its release kinetics were modified in the aqueous medium. The microcapsules coated with rubber had a slow release when compared to uncoated microcapsules. In a similar release duration of 24 h, the uncoated nanocapsules exhibited a 100% release of the azadirachtin while the coated nanocapsules released 80%. The successful encapsulation of azadirachtin in the alginate particles offered potential for future agricultural applications. Another recently described strategy is a poly(ε-caprolactone) (PCL) formulation constituting azadirachtin in a powder form using the spray-drying method (Forim et al., 2013). The nanometric particles were subjected to characterization in terms of size, shape, surface charge, and the encapsulation efficacy. This encapsulated nanoformulation (size range 20–30 nm) gave 98% efficacy against P. xylostella and possessed potent temporal stability, which was an indication for its robust application. The spherical shape of the particles was confirmed through scanning electron microscopy, which also revealed that the active agent release was due to the erosion of the polymer or via slackening of the polymeric chains. Similarly, as per da Costa et  al. (2014), the preparation of various types of nanoformulations such as nanocapsules, emulsions, and microparticles was carried out using azadirachtin as the

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a­ ctive ingredient. The study was based on UV radiation stability. It was observed that the nanometric capsule exhibited higher stability in comparison to the commercially available products. However, the emulsion system displayed the higher biological efficacy in comparison with nanocapsules and microparticles when evaluated against Zabrotes subfasciatus (da Costa et al., 2014).

6.6 ­ Rotenone-Based Nanocomposites Martin et  al. (2013) examined the rotenone encapsulation through biodegradable polymers using a process termed supercritical assisted atomization (SAA). In this experimentation, three varieties of polymers—sodium alginate, polyethylene glycol (PEG), and poly-vinyl pyrrolidone (PVP)—were analyzed. These polymerbased biopesticidal formulations were formulated with an average particle size of 0.6–1.5 μm. The finest encapsulation efficacy was achieved for the alginate/rotenone combination (100%) while for PEG/rotenone it was 98% and only 30%–50% in the case of the microparticles comprising the PVP/rotenone. The application of the ­polymer-based rotenone nanocapsules provided significant control under field conditions (Martin et al., 2013).

6.7 ­ Monoterpene-Based Nanocomposites Another variety of nanoencapsulation was achieved using the active ingredient carvacrol, which is a phenolic chemical component present in the oils of thyme and oregano. Keawchaoon and Yoksan (2011) described the formulation of nanometric particles using chitosan/(TPP) penta sodium tripolyphosphate with carvacrol. This product was highly efficacious against microbes such as Staphylococcus aureus, Bacillus cereus, and Escherichia coli in comparison to chitosan encapsulates alone. Potent applicative strategies of carvacrol make it a propitious compound that can be used in food-processing industries. Similarly, Zein-derived nanometric particles stabilized with chitosan hydrochloride (CHC) and sodium caseinate (SC) have been used to encapsulate thymol (Zhang et  al., 2014). The SC stabilized nanoparticles had a well-defined size range and a negatively charged surface. Due to the presence of SC, the stabilized zein nanoparticles provided desirable redispersibility in water at neutral pH after lyophilization. Coating with CHC onto the SC-stabilized zein nanoparticles improved encapsulation efficiency. However, there was variation in the shape and size of nanoparticles. Thymol-loaded zein nanoparticles and SCstabilized zein nanoparticles had a spherical shape and smooth surface while CHCSC-stabilized zein nanoparticles were apparently rough and clumpy. Encapsulated thymol was more effective in suppressing gram-positive bacterium than unencapsulated thymol for a longer time period (Zhang et al., 2014). Thymol has significant insecticidal activity as well (Koul et al., 2008) and such nanoformulations can provide a significant delivery strategy for the control of insect pests.

6.8 ­ Essential oil-based nanocomposites

Similarly, Sajomsang et  al. (2012) formulated and characterized hydrosoluble derivatives of chitosan in combination with (DC-CD) β-cyclodextrin as haulers of the active ingredient eugenol (EG). The particles of DC-CD exhibited a higher efficacy of antimicrobial activity against Streptococcus oralis, Streptococcus mutans, and Candida albicans in comparison to β-cyclodextrin alone. Curcumin is a phenolic component present in multiple plant species, notably in the turmeric, which can be extracted from the rhizomes (Irving et al., 2011). Bielska et al. (2013) used polymeric derivatives of hydroxypropyl cellulose (HPC), which can be either anionic (modified with styrene groups) or cationic (modified with trimethylammonium groups), to formulate curcumin-based nanoproducts. These heat-sensitive polymeric compounds exhibited higher notches of substitution, which enabled them to be applied for the preparation of curcumin-based nanoparticles for various applications in the food, agriculture, and health industries.

6.8 ­Essential Oil-Based Nanocomposites EOs are volatile oily liquids obtained from different plant parts that are widely used as food flavors. However, a number of studies have demonstrated that EOs can be used as green pesticides (Koul et  al., 2008). However, their quick biodegradable nature constrains their delivery. One of the most effective alternatives to improve this property is to use biopolymer films and the development of nanocomposites. Owing to the reinforcement provided by the nanometer-sized particles dispersed in the biopolymer material, polymer nanocomposites—especially natural biopolymerlayered silicate nanocomposites—exhibit markedly improved strategies compared with pure biopolymer (Petersson and Oksman, 2006). It has been established that barrier properties imparted by the nanocomposite matrix and the antimicrobial or antipest properties contributed by the natural product agents impregnated within play a significant role (Abdollahi et al., 2012). In this way, the nanocomposite can be a vehicle to release active compounds slowly and would also help in the retention of aromatic compounds, as shown in studies of nanoclays in films (Kurek et al., 2012). The benefits of the essential oil applications include the incidence of various chemical constituents that can exhibit synergistic effects with the presence of the core active constituent in the oil system (Jiang et al., 2009). Lai et al. (2006) described the preparation strategy of solid lipid nanoparticles (SLNs) comprising the tree wormwood essential oil (Artemisia arborescens) for agricultural applications. The two different varieties of SLNs were formulated using the process of high-pressure homogenization, retaining the applicative role of surfactantlike Miranol Ultra C32 and Poloxamer 188. The prepared formulations exhibited higher stability at various physiochemical conditions, making them promising as bio-based insecticides in the agricultural sector. Yang et al. (2009) described the formulation strategy of PEG-mediated synthesis of nanoparticles loaded with garlic oil (Allium sativum). The efficacy of this nanoformulation was carried out against the red flour beetle (T. castaneum). This essential

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oil of garlic contains diallyl disulfide and trisulfide, which are larvicidal. Similarly, Varona et  al. (2010) manifested two varieties of polymeric encapsulations using modified starch and PEG of lavender oil. The prepared encapsulation strategy provided a controlled release of the active ingredient. The formulation process via this kind of encapsulation method provided an essential transporter for the lavender oil to be used as an insect repellent. The application of the coacervation method has been carried out by Dong et al. (2011) to formulate microcapsules of gum Arabic and gelatine with transglutaminase as a hardening agent. The peppermint oil was used as the encapsulating material. The high degree of stability and release kinetics of the active constituent make this nanoformulation a useful biocontrol agent. Likewise, Abreu et al. (2012) described the application of nanogel synthesis using cashew gum and chitosan as an encapsulating agent and peppermint oil as the encapsulate. The good release kinetics and higher stability with strong efficacy make this nanoformulation an effective larvicidal agent against mosquitoes. Hosseini et  al. (2013) described the nanoparticle formulation using chitosan through the oil-in-water emulsification process and the gelification process of chitosan using TPP (sodium tripolyphosphate). Jouki et al. (2014) provided the preparation methodology of thin films based on the quince seeds mucilage with the thyme oil. The experimental studies have proven the antibacterial and antioxidant properties of this formulation, which can be applied in various commercial and agricultural sectors. Fernandes et al. (2014) examined the application of different polymeric matrices, for example, gum Arabic, maltodextrin, modified starch, and inulin as encapsulating materials for rosemary essential oil. The experimental results specified the efficacy of these polymeric compounds, which could be applied in agricultural and various other sectors.

6.9 ­ Silicate Nanocomposites for Entomopathogens Bioinsecticides based on entomopathogenic fungi have been in use for decades now; however, conidia produced by these fungi are very sensitive to abiotic factors. One of the stragies to overcome this is their encapsulation in order to prevent a fungal matrix. Encapsulation in polymer matrices adds value to the product, which preserves their properties and viability. Nanostructured materials may have all the crystallites and interface boundaries with the same chemical composition or not, resulting in structures known as nanocomposites. In fact, polymer nanocomposites are two-phase materials with one phase formed by nanoparticles (fillers) dispersed in a polymer matrix, which is the continuous phase (Ma et al., 2012). Different nanofillers may be incorporated into the polymer matrix; when the filler is a philosilicate clay such as bentonite, the material is generically called polymer/layered silicate nanocomposite (PLN). These lamellar silicates present crystalline lamellae in the nanometric scale that are two-dimensionally arranged on top of each other (Ray and Bousmina, 2005). Due to current encouragement for the use of bioinsecticides for pest control and the susceptibility of biological

6.10 ­ Conclusion

agents to external factors, several investigations have shown the potential of PLN as a matrix to encapsulate an entomopathogenic fungus active against pest insects. One of the case studies given here suggests the significance of this strategy. The study is based on the use of PLN to encapsulate an entomopathogenic fungus active against pest insects of palm trees. The beads were formed by extrusion and three fungus conidia concentrations and nanolayered silicate concentrations were used. The matrix was evaluated by X-ray powder diffraction and Fourier transform infrared spectroscopy. The characteristics of the products were assessed: percent of encapsulated conidia, size distribution and polydispersity index, swelling index, in vitro ability of the formulation to release conidia, and stability under different storage temperatures. PLN, whose interactions could be visualized by FTIR, proved to be a potential matrix for this fungus because, while composed of natural substances that are nontoxic to the environment, it succeeded in encapsulating high amounts of conidia. A barrier effect with a bentonite increase was also demonstrated by increased fungus germination time and thermal stability (Batista et al., 2014). Apparently, matrix encapsulation has the ability to incorporate conidia at higher concentrations without affecting germination. This has significant positive implications in integrated pest management. Another good example is that of PLN of alginate bentonite as a bead matrix for the entomopathogenic fungus Beauveria bassiana strain CPATC032. However, in this study it was demonstrated that the in  vitro release of the fungus is sensitive to the bead preparation method due to the emergence of a barrier phenomenon as the concentration of silicate is increased. Swelling degree and release kinetics were also investigated, where a strong dependence on the drying method was observed (Batista et al., 2017). Therefore, it is obvious that various applications of nanocomposites as pesticides have significant potential in pest control. However, the issues of ecological wellbeing upon application of these nanomaterials need to be standardized with complete regulations followed. To confirm the efficiency, a majority of these nanometric insecticides have been formulated for control release and exhibiting their perseverance in the environmental conditions (Fig. 6.2). Therefore, it is a vital step to study the ecological providence processes for all varieties of nanoproducts. This strategy of encapsulation of pesticides using polymeric compounds can, therefore, become an essential tool for integrated pest management.

6.10 ­Conclusion The studies mentioned above show that the application of natural products for pest management can be delivered with pronounced stability if nanocomposites are used as the matrix. The encapsulation strategy of these active ingredients in bio-based polymers is a practical approach toward providing stability to botanical insecticides as well as a slow release of these active chemical constituents, making these products potent tools for targeted delivery. This chapter has provided current viewpoints of the nanocomposite systems for enhancement of bio-derived pesticides. The nanotechnology

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FIG. 6.2 Nanotechnological approach toward bio-based pesticide formulation with a polymer matrix for pest-control strategies.

approach is thought provoking because it can help alleviate the adverse influences of conventional pesticides and other agrochemicals toward human health and the environment. Therefore, as a consequence, there has been a considerable upsurge in research activity in this field. There are significant advantages of polymer layered/silicate nanocomposites. They generally exhibit improved mechanical properties compared to conventional composites; they possess increased thermal stability and provide reduced permeability. For these reasons, PLS nanocomposites are far lighter in weight than conventional composites, making them competitive with other materials for specific applications. The unique combination of their key properties and potentially low production costs paves the way for a wide range of applications. However, drawbacks that need to be studied before commercialization include the issue of scalability of the nanocarrier formulation as well as the discovery of biomatrices to hold such active ingredients. The strategic approach via the application of nanotechnology tools can also help in reducing the conventional pesticide load.

­Acknowledgment We acknowledge the Vellore Institute of Technology for providing laboratory space and facilities.

­References

­Conflict of Interest The authors declare that they have no conflicts of interest.

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­Further Reading Aldridge, W.N., 1990. An assessment of the toxicological properties of pyrethroids and their neurotoxicity. Crit. Rev. Toxicol. 21, 89–104. Bond, C., Buhl, K., Stone, D., 2014. Pyrethrins General Fact Sheet; National Pesticide Information Center. Oregon State University Extension Services, Oregon. Bradbury, S.P., Coats, J.R., 1989. Comparative toxicology of the pyrethroid insecticides. Rev. Environ. Contam. Toxicol. 108, 133–177. Campos, E.V.R., de Oliveira, J.L., Fraceto, L.F., 2014. Applications of controlled release systems for fungicides, herbicides, acaricides, nutrients, and plant growth hormones: a review. Adv. Sci. Eng. Med. 6, 373–387. Mandhane, S.N., Chopde, C.T., 1997. Neurobehavioral effects of low-level fenvalerate exposure in mice. Indian J. Exp. Biol. 35, 623–627. Todd, G.D., Wohlers, D., Citra, M.J., 2003. Toxicological Profile for Pyrethrins and Pyrethroids. Agency for Toxic Substances and Disease Registry. Vijverberg, H.P., van der Zalm, J.M., van den Bercken, J., 1982. Similar mode of action of pyrethroids and DDT on sodium channel gating in myelinated nerves. Nature 295, 601–603.